geom_algorithms.H

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
#ifndef GEOM_ALGORITHMS_H
#define GEOM_ALGORITHMS_H
 
#include <sstream>
#include <polygon.H>
#include <htlist.H>
#include <tpl_dynDlist.H>
#include <tpl_dynSetTree.H>
#include <tpl_arrayQueue.H>
#include <tpl_arrayStack.H>
#include <tpl_sort_utils.H>
#include <tpl_2dtree.H>
#include <ah-errors.H>
#include <algorithm>
#include <utility>
#include <random>
#include <map>
#include <set>
#include <queue>
#include <memory>
#include <limits>
#include <cmath>
 
#include <ah-unique.H>
#include <tpl_dynBinHeap.H>
 
namespace Aleph {
class GeomPolygonUtils
{
public:
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &poly)
  {
    Array<Point> verts;
    verts.reserve(poly.size());
    for (Polygon::Vertex_Iterator it(poly); it.has_curr(); it.next_ne())
      verts.append(it.get_current_vertex());
    return verts;
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Array<Point> &verts)
  {
    Geom_Number sum = 0;
    for (size_t i = 0; i < verts.size(); ++i)
      {
        const Point &a = verts(i);
        const Point &b = verts((i + 1) % verts.size());
        sum += a.get_x() * b.get_y() - a.get_y() * b.get_x();
      }
    return sum;
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Polygon &poly)
  {
    return signed_double_area(extract_vertices(poly));
  }
 
  [[nodiscard]] static Geom_Number signed_area(const Array<Point> &verts)
  {
    return signed_double_area(verts) / 2;
  }
 
  [[nodiscard]] static Geom_Number signed_area(const Polygon &poly)
  {
    return signed_double_area(poly) / 2;
  }
 
  [[nodiscard]] static Geom_Number area(const Array<Point> &verts)
  {
    Geom_Number a = signed_area(verts);
    return a < 0 ? Geom_Number(-a) : a;
  }
 
  [[nodiscard]] static Geom_Number area(const Polygon &poly)
  {
    Geom_Number a = signed_area(poly);
    return a < 0 ? Geom_Number(-a) : a;
  }
 
  [[nodiscard]] static bool is_convex(const Array<Point> &verts)
  {
    if (verts.size() < 3)
      return true;
 
    int sign = 0;
    const size_t n = verts.size();
    for (size_t i = 0; i < n; ++i)
      {
        const Geom_Number turn =
          area_of_parallelogram(verts(i), verts((i + 1) % n), verts((i + 2) % n));
        if (turn == 0)
          continue;
        const int curr = turn > 0 ? 1 : -1;
        if (sign == 0)
          sign = curr;
        else if (sign != curr)
          return false;
      }
    return true;
  }
 
  static void ensure_ccw(Array<Point> &verts)
  {
    if (signed_double_area(verts) < 0)
      for (size_t i = 0; i < verts.size() / 2; ++i)
        {
          const Point tmp = verts(i);
          verts(i) = verts(verts.size() - 1 - i);
          verts(verts.size() - 1 - i) = tmp;
        }
  }
};
 
class GeomTriangleAdjacencyUtils
{
public:
  struct EdgeRef
  {
    size_t u;      
    size_t v;      
    size_t tri;    
    size_t third;  
  };
 
private:
  static void append_edge(Array<EdgeRef> &edges, size_t a, size_t b, const size_t tri, const size_t third)
  {
    if (a > b)
      {
        const size_t tmp = a;
        a = b;
        b = tmp;
      }
 
    edges.append(EdgeRef{a, b, tri, third});
  }
 
public:
  template <typename TriangleArray, typename GroupFn>
  static void for_each_sorted_edge_group(const TriangleArray &triangles, GroupFn on_group)
  {
    Array<EdgeRef> edges;
    edges.reserve(triangles.size() * 3);
    for (size_t tri_idx = 0; tri_idx < triangles.size(); ++tri_idx)
      {
        const auto &tri = triangles(tri_idx);
        append_edge(edges, tri.i, tri.j, tri_idx, tri.k);
        append_edge(edges, tri.j, tri.k, tri_idx, tri.i);
        append_edge(edges, tri.k, tri.i, tri_idx, tri.j);
      }
 
    quicksort_op(edges, [](const EdgeRef &a, const EdgeRef &b)
      {
        if (a.u != b.u)
          return a.u < b.u;
        if (a.v != b.v)
          return a.v < b.v;
        return a.tri < b.tri;
      });
 
    size_t first = 0;
    while (first < edges.size())
      {
        size_t last = first + 1;
        while (last < edges.size() and edges(last).u == edges(first).u and
               edges(last).v == edges(first).v)
          ++last;
 
        on_group(edges, first, last);
        first = last;
      }
  }
};
 
class GeomBowyerWatsonUtils
{
private:
  struct WorkTriangle
  {
    size_t a;
    size_t b;
    size_t c;
    bool alive;
  };
 
  struct UndirectedEdge
  {
    size_t u;
    size_t v;
  };
 
  struct CmpUndirectedEdge
  {
    bool operator () (const UndirectedEdge &a, const UndirectedEdge &b) const
    {
      if (a.u != b.u)
        return a.u < b.u;
      return a.v < b.v;
    }
  };
 
  using EdgeSet = DynSetTree<UndirectedEdge, Treap_Rk, CmpUndirectedEdge>;
 
  static void toggle_edge(EdgeSet &boundary, size_t u, size_t v)
  {
    if (u > v)
      {
        const size_t tmp = u;
        u = v;
        v = tmp;
      }
 
    const UndirectedEdge e{u, v};
    if (const auto *ptr = boundary.search(e); ptr != nullptr)
      boundary.remove(*ptr);
    else
      boundary.insert(e);
  }
 
public:
  template <typename IndexedTriangle, typename InCirclePredicate>
  [[nodiscard]] static Array<IndexedTriangle> triangulate(Array<Point> pts,
                                                          const size_t n,
                                                          InCirclePredicate point_in_circumcircle)
  {
    Array<IndexedTriangle> out;
    if (n < 3)
      return out;
 
    Geom_Number minx = pts(0).get_x();
    Geom_Number maxx = pts(0).get_x();
    Geom_Number miny = pts(0).get_y();
    Geom_Number maxy = pts(0).get_y();
 
    for (size_t i = 1; i < n; ++i)
      {
        if (pts(i).get_x() < minx)
          minx = pts(i).get_x();
        if (pts(i).get_x() > maxx)
          maxx = pts(i).get_x();
        if (pts(i).get_y() < miny)
          miny = pts(i).get_y();
        if (pts(i).get_y() > maxy)
          maxy = pts(i).get_y();
      }
 
    const Geom_Number dx = maxx - minx;
    const Geom_Number dy = maxy - miny;
    Geom_Number delta = dx > dy ? dx : dy;
    if (delta == 0)
      delta = 1;
 
    const Geom_Number span = delta * 16 + 1;
    const Geom_Number two_span = span + span;
    const Geom_Number midx = (minx + maxx) / 2;
    const Geom_Number midy = (miny + maxy) / 2;
 
    const Point s0(midx - two_span, midy - span);
    const Point s1(midx + two_span, midy - span);
    const Point s2(midx, midy + two_span);
 
    pts.append(s0);
    pts.append(s1);
    pts.append(s2);
 
    const size_t i0 = n;
    const size_t i1 = n + 1;
    const size_t i2 = n + 2;
 
    Array<WorkTriangle> work;
    work.append(WorkTriangle{i0, i1, i2, true});
 
    for (size_t pidx = 0; pidx < n; ++pidx)
      {
        Array<size_t> bad;
        bad.reserve(work.size());
 
        for (size_t t = 0; t < work.size(); ++t)
          {
            const auto &[a, b, c, alive] = work(t);
            if (not alive)
              continue;
 
            if (point_in_circumcircle(pts, a, b, c, pidx))
              bad.append(t);
          }
 
        if (bad.is_empty())
          continue;
 
        EdgeSet boundary;
 
        for (size_t bad_idx = 0; bad_idx < bad.size(); ++bad_idx)
          {
            auto &[a, b, c, alive] = work(bad(bad_idx));
            if (not alive)
              continue;
 
            toggle_edge(boundary, a, b);
            toggle_edge(boundary, b, c);
            toggle_edge(boundary, c, a);
            alive = false;
          }
 
        boundary.for_each([&](const UndirectedEdge &edge)
          {
            size_t u = edge.u;
            size_t v = edge.v;
 
            const Orientation o = orientation(pts(u), pts(v), pts(pidx));
            if (o == Orientation::COLLINEAR)
              return;
 
            if (o == Orientation::CW)
              {
                const size_t tmp = u;
                u = v;
                v = tmp;
              }
 
            work.append(WorkTriangle{u, v, pidx, true});
          });
 
        Array<WorkTriangle> compacted;
        compacted.reserve(work.size());
        for (size_t t = 0; t < work.size(); ++t)
          if (work(t).alive)
            compacted.append(work(t));
        work = std::move(compacted);
      }
 
    out.reserve(work.size());
    for (size_t t = 0; t < work.size(); ++t)
      {
        const auto &[a, b, c, alive] = work(t);
        if (not alive)
          continue;
 
        if (a >= n or b >= n or c >= n)
          continue;
 
        if (orientation(pts(a), pts(b), pts(c)) == Orientation::COLLINEAR)
          continue;
 
        out.append(IndexedTriangle{a, b, c});
      }
 
    return out;
  }
};
 
// ============================================================================
// Triangulation Algorithms
// ============================================================================
 
class CuttingEarsTriangulation
{
  using EarsSet = DynSetTree<const Vertex *, Treap_Rk>;
 
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &p)
  {
    return GeomPolygonUtils::extract_vertices(p);
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Polygon &p)
  {
    return GeomPolygonUtils::signed_double_area(p);
  }
 
  static void normalize_to_ccw(Polygon &p)
  {
    const Geom_Number area2 = signed_double_area(p);
    ah_domain_error_if(area2 == 0) << "Polygon is degenerate (zero area)";
    if (area2 > 0)
      return;
 
    const Array<Point> verts = extract_vertices(p);
    Polygon ccw;
    for (size_t i = verts.size(); i > 0; --i)
      ccw.add_vertex(verts(i - 1));
    ccw.close();
    p = std::move(ccw);
  }
 
public:
  static bool diagonalize(const Polygon &p, const Segment &s)
  {
    for (Polygon::Segment_Iterator it(p); it.has_curr(); it.next_ne())
      if (Segment curr = it.get_current_segment(); curr.get_src_point() != s.get_src_point() and
          curr.get_tgt_point() != s.get_src_point() and curr.get_src_point() != s.get_tgt_point() and
          curr.get_tgt_point() != s.get_tgt_point() and s.intersects_with(curr))
        return false;
    return true;
  }
 
  static bool in_cone(const Polygon &p, const Vertex &a, const Vertex &b)
  {
    // a0 -> a -> a1 are consecutive vertices
    const Vertex &a0 = p.get_prev_vertex(a);
    const Vertex &a1 = p.get_next_vertex(a);
 
    if (a0.is_to_left_on_from(a, a1))
      return a0.is_left_of(a, b) and a1.is_left_of(b, a);
 
    return not (a1.is_to_left_on_from(a, b) and a0.is_to_left_on_from(b, a));
  }
 
  static bool diagonal(const Polygon &p, const Vertex &a, const Vertex &b)
  {
    return in_cone(p, a, b) and in_cone(p, b, a) and
      diagonalize(p, Segment(a.to_point(), b.to_point()));
  }
 
  static EarsSet init_ears(const Polygon &p)
  {
    EarsSet ret;
 
    for (Polygon::Vertex_Iterator it(p); it.has_curr(); it.next_ne())
      {
        Vertex &curr = it.get_current_vertex();
        const Vertex &prev = p.get_prev_vertex(curr);
        if (const Vertex &next = p.get_next_vertex(curr); diagonal(p, prev, next))
          ret.insert(&curr);
      }
 
    return ret;
  }
 
public:
  DynList<Triangle> operator () (const Polygon &poly) const
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(poly.size() < 3) << "Polygon has less than 3 vertices";
 
    Polygon p = poly;  // work on a copy
    normalize_to_ccw(p);
 
    EarsSet ears;
    if (p.size() > 3)
      {
        ears = init_ears(p);
        ah_domain_error_if(ears.is_empty()) << "No valid ear found; polygon may be non-simple";
      }
 
    DynList<Triangle> ret;
 
    while (p.size() > 3)
      {
        ah_domain_error_if(ears.is_empty()) << "No valid ear found during triangulation";
        const Vertex *curr = ears.remove_pos(0);
 
        const Vertex &prev = p.get_prev_vertex(*curr);
        const Vertex &next = p.get_next_vertex(*curr);
 
        ret.append(Triangle(prev.to_point(), curr->to_point(), next.to_point()));
        p.remove_vertex(*curr);
 
        // After removal, prev and next are adjacent; recompute their
        // outer neighbors for ear tests on the updated topology.
        const Vertex &new_prev_prev = p.get_prev_vertex(prev);
        const Vertex &new_next_next = p.get_next_vertex(next);
 
        if (diagonal(p, new_prev_prev, next))
          ears.insert(&prev);
        else
          ears.remove(&prev);
 
        if (diagonal(p, prev, new_next_next))
          ears.insert(&next);
        else
          ears.remove(&next);
      }
 
    assert(p.size() == 3);
 
    const Vertex &a = p.get_first_vertex();
    const Vertex &b = a.next_vertex();
    const Vertex &c = b.next_vertex();
 
    ret.append(Triangle(a.to_point(), b.to_point(), c.to_point()));
 
    return ret;
  }
};
 
// ============================================================================
// Closest Pair of Points
// ============================================================================
 
class ClosestPairDivideAndConquer
{
public:
  struct Result
  {
    Point first;
    Point second;
    Geom_Number distance_squared;
  };
 
private:
  struct LexicographicCmp
  {
    bool operator () (const Point &p1, const Point &p2) const
    {
      if (p1.get_x() < p2.get_x())
        return true;
 
      if (p2.get_x() < p1.get_x())
        return false;
 
      return p1.get_y() < p2.get_y();
    }
  };
 
  struct ByYCmp
  {
    bool operator () (const Point &p1, const Point &p2) const
    {
      if (p1.get_y() < p2.get_y())
        return true;
 
      if (p2.get_y() < p1.get_y())
        return false;
 
      if (p1.get_x() < p2.get_x())
        return true;
 
      if (p2.get_x() < p1.get_x())
        return false;
 
      return false;
    }
  };
 
  [[nodiscard]] static Geom_Number dist2(const Point &a, const Point &b)
  {
    return a.distance_squared_to(b);
  }
 
  [[nodiscard]] static Result make_result(const Point &a, const Point &b)
  {
    return {a, b, dist2(a, b)};
  }
 
  [[nodiscard]] static Result brute_force(const Array<Point> &px, const size_t l, const size_t r)
  {
    assert(r - l >= 2);
 
    Result best = make_result(px(l), px(l + 1));
 
    for (size_t i = l; i < r; ++i)
      for (size_t j = i + 1; j < r; ++j)
        if (Result cand = make_result(px(i), px(j)); cand.distance_squared < best.distance_squared)
          best = cand;
 
    return best;
  }
 
  [[nodiscard]] static Result recurse(const Array<Point> &px,
                                      const size_t l,
                                      const size_t r,
                                      Array<Point> &py)
  {
    const size_t n = r - l;
    if (n <= 3)
      return brute_force(px, l, r);
 
    const size_t mid = l + n / 2;
    const Point &mid_point = px(mid);
 
    Array<Point> left_py;
    Array<Point> right_py;
    left_py.reserve(mid - l);
    right_py.reserve(r - mid);
 
    const size_t left_target = mid - l;
    for (size_t i = 0; i < py.size(); ++i)
      {
        const Point &p = py(i);
        if (p.get_x() < mid_point.get_x())
          left_py.append(p);
        else if (p.get_x() > mid_point.get_x())
          right_py.append(p);
        else  // tie on x — fill left first, then right
          {
            if (left_py.size() < left_target)
              left_py.append(p);
            else
              right_py.append(p);
          }
      }
 
    const Result best_left = recurse(px, l, mid, left_py);
    const Result best_right = recurse(px, mid, r, right_py);
    Result best = best_left.distance_squared < best_right.distance_squared ? best_left : best_right;
 
    Array<Point> strip;
    strip.reserve(py.size());
    for (size_t i = 0; i < py.size(); ++i)
      {
        const Point &p = py(i);
        if (const Geom_Number dx = p.get_x() - mid_point.get_x(); dx * dx < best.distance_squared)
          strip.append(p);
      }
 
    for (size_t i = 0; i < strip.size(); ++i)
      for (size_t j = i + 1; j < strip.size(); ++j)
        {
          if (const Geom_Number dy = strip(j).get_y() - strip(i).get_y();
              dy * dy >= best.distance_squared)
            break;
 
          if (Result cand = make_result(strip(i), strip(j));
              cand.distance_squared < best.distance_squared)
            best = cand;
        }
 
    return best;
  }
 
public:
  [[nodiscard]] Result operator () (const DynList<Point> &point_set) const
  {
    Array<Point> px;
    for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
      px.append(it.get_curr());
 
    ah_domain_error_if(px.size() < 2) << "Closest pair requires at least 2 points";
 
    quicksort_op(px, LexicographicCmp());
 
    // Early-exit on duplicate points: exact minimum distance is zero.
    for (size_t i = 1; i < px.size(); ++i)
      if (px(i) == px(i - 1))
        return {px(i - 1), px(i), 0};
 
    Array<Point> py = px;
    quicksort_op(py, ByYCmp());
 
    return recurse(px, 0, px.size(), py);
  }
 
  [[nodiscard]] Segment closest_segment(DynList<Point> &point_set) const
  {
    Result r = (*this)(point_set);
    return {r.first, r.second};
  }
};
 
// ============================================================================
// Minimum Enclosing Circle (Welzl)
// ============================================================================
 
class MinimumEnclosingCircle
{
public:
  struct Circle
  {
    Point center;
    Geom_Number radius_squared = 0;
 
    [[nodiscard]] Geom_Number radius() const
    {
      return square_root(radius_squared);
    }
 
    [[nodiscard]] bool contains(const Point &p) const
    {
      return center.distance_squared_to(p) <= radius_squared;
    }
  };
 
  [[nodiscard]] static Circle from_one_point(const Point &a)
  {
    return {a, 0};
  }
 
  [[nodiscard]] static Circle from_two_points(const Point &a, const Point &b)
  {
    const Point c = a.midpoint(b);
    return {c, c.distance_squared_to(a)};
  }
 
  [[nodiscard]] static Circle from_three_points(const Point &a, const Point &b, const Point &c)
  {
    const Geom_Number &ax = a.get_x();
    const Geom_Number &ay = a.get_y();
    const Geom_Number &bx = b.get_x();
    const Geom_Number &by = b.get_y();
    const Geom_Number &cx = c.get_x();
    const Geom_Number &cy = c.get_y();
 
    const Geom_Number d = ax * (by - cy) + bx * (cy - ay) + cx * (ay - by);
 
    if (d == 0)  // collinear — return diameter of farthest pair
      {
        const Geom_Number d_ab = a.distance_squared_to(b);
        const Geom_Number d_bc = b.distance_squared_to(c);
        const Geom_Number d_ac = a.distance_squared_to(c);
 
        if (d_ab >= d_bc && d_ab >= d_ac)
          return from_two_points(a, b);
        if (d_bc >= d_ab && d_bc >= d_ac)
          return from_two_points(b, c);
        return from_two_points(a, c);
      }
 
    const Geom_Number den = d + d;
    const Geom_Number a2 = ax * ax + ay * ay;
    const Geom_Number b2 = bx * bx + by * by;
    const Geom_Number c2 = cx * cx + cy * cy;
 
    const Geom_Number ux = (a2 * (by - cy) + b2 * (cy - ay) + c2 * (ay - by)) / den;
    const Geom_Number uy = (a2 * (cx - bx) + b2 * (ax - cx) + c2 * (bx - ax)) / den;
 
    const Point center{ux, uy};
    return {center, center.distance_squared_to(a)};
  }
 
  [[nodiscard]] Circle operator () (const DynList<Point> &points) const
  {
    Array<Point> pts;
    for (DynList<Point>::Iterator it(points); it.has_curr(); it.next_ne())
      pts.append(it.get_curr());
 
    ah_domain_error_if(pts.size() == 0) << "MinimumEnclosingCircle: empty point set";
 
    // Fisher-Yates shuffle
    {
      std::random_device rd;
      std::mt19937 gen(rd());
      for (size_t i = pts.size() - 1; i > 0; --i)
        {
          std::uniform_int_distribution<size_t> dist(0, i);
          if (const size_t j = dist(gen); i != j)
            std::swap(pts(i), pts(j));
        }
    }
 
    return welzl_iterative(pts);
  }
 
  [[nodiscard]] Circle operator () (std::initializer_list<Point> points) const
  {
    DynList<Point> l;
    for (const auto &p : points)
      l.append(p);
    return (*this)(l);
  }
 
private:
  [[nodiscard]] static Circle mec_with_point(const Array<Point> &pts, size_t n, const Point &p1)
  {
    Circle d = from_one_point(p1);
    for (size_t j = 0; j < n; ++j)
      if (not d.contains(pts(j)))
        d = mec_with_two_points(pts, j, p1, pts(j));
    return d;
  }
 
  [[nodiscard]] static Circle mec_with_two_points(const Array<Point> &pts,
                                                  size_t n,
                                                  const Point &p1,
                                                  const Point &p2)
  {
    Circle d = from_two_points(p1, p2);
    for (size_t k = 0; k < n; ++k)
      if (not d.contains(pts(k)))
        d = from_three_points(p1, p2, pts(k));
    return d;
  }
 
  [[nodiscard]] static Circle welzl_iterative(const Array<Point> &pts)
  {
    Circle d = from_one_point(pts(0));
 
    for (size_t i = 1; i < pts.size(); ++i)
      if (not d.contains(pts(i)))
        d = mec_with_point(pts, i, pts(i));
 
    return d;
  }
};
 
// ============================================================================
// Rotating Calipers (Convex Polygon Metrics)
// ============================================================================
 
class RotatingCalipersConvexPolygon
{
public:
  struct DiameterResult
  {
    Point first;
    Point second;
    Geom_Number distance_squared;
  };
 
  struct WidthResult
  {
    Point edge_first;
    Point edge_second;
    Point antipodal;
    Geom_Number width_squared;
  };
 
private:
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &poly)
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
 
    ah_domain_error_if(poly.size() < 2) << "Rotating calipers requires at least 2 vertices";
 
    return GeomPolygonUtils::extract_vertices(poly);
  }
 
  [[nodiscard]] static bool is_convex(const Array<Point> &verts)
  {
    return GeomPolygonUtils::is_convex(verts);
  }
 
  [[nodiscard]] static DiameterResult make_diameter(const Point &a, const Point &b)
  {
    return {a, b, a.distance_squared_to(b)};
  }
 
public:
  static DiameterResult diameter(const Polygon &poly)
  {
    const Array<Point> verts = extract_vertices(poly);
    ah_domain_error_if(not is_convex(verts)) << "Polygon must be convex";
 
    const size_t n = verts.size();
    if (n == 2)
      return make_diameter(verts(0), verts(1));
 
    auto edge_area = [&verts, n](const size_t i, const size_t k) -> Geom_Number
      {
        Geom_Number area = area_of_parallelogram(verts(i), verts((i + 1) % n), verts(k));
        if (area < 0)
          area = -area;
        return area;
      };
 
    size_t j = 1;
    size_t safety = 0;
    while (edge_area(0, (j + 1) % n) > edge_area(0, j) and safety++ < n)
      j = (j + 1) % n;
 
    DiameterResult best = make_diameter(verts(0), verts(j));
 
    for (size_t i = 0; i < n; ++i)
      {
        const size_t ni = (i + 1) % n;
        safety = 0;
        while (edge_area(i, (j + 1) % n) > edge_area(i, j) and safety++ < n)
          j = (j + 1) % n;
 
        if (DiameterResult cand1 = make_diameter(verts(i), verts(j));
            cand1.distance_squared > best.distance_squared)
          best = cand1;
 
        if (DiameterResult cand2 = make_diameter(verts(ni), verts(j));
            cand2.distance_squared > best.distance_squared)
          best = cand2;
      }
 
    return best;
  }
 
  static WidthResult minimum_width(const Polygon &poly)
  {
    const Array<Point> verts = extract_vertices(poly);
    ah_domain_error_if(not is_convex(verts)) << "Polygon must be convex";
 
    const size_t n = verts.size();
    if (n == 2)
      return {verts(0), verts(1), verts(0), 0};
 
    auto area_to_edge = [&verts, n](const size_t i, const size_t k) -> Geom_Number
      {
        Geom_Number area = area_of_parallelogram(verts(i), verts((i + 1) % n), verts(k));
        if (area < 0)
          area = -area;
        return area;
      };
 
    auto edge_len2 = [&verts, n](const size_t i) -> Geom_Number
      {
        return verts(i).distance_squared_to(verts((i + 1) % n));
      };
 
    size_t best_i = 0;
    size_t best_ni = 1;
    size_t best_j = 0;
    Geom_Number best_width_sq = 0;
    bool initialized = false;
 
    // Initialize antipodal index for edge (0,1).
    size_t j = 1 % n;
    size_t safety = 0;
    while (area_to_edge(0, (j + 1) % n) > area_to_edge(0, j) and safety++ < n)
      j = (j + 1) % n;
 
    for (size_t i = 0; i < n; ++i)
      {
        const size_t ni = (i + 1) % n;
 
        const Geom_Number len2 = edge_len2(i);
        if (len2 == 0)
          continue;
 
        // Advance antipodal index while area increases.
        safety = 0;
        while (area_to_edge(i, (j + 1) % n) > area_to_edge(i, j) and safety++ < n)
          j = (j + 1) % n;
 
        const Geom_Number num = area_to_edge(i, j);
        const Geom_Number width_sq = (num * num) / len2;
        if (not initialized or width_sq < best_width_sq)
          {
            best_i = i;
            best_ni = ni;
            best_j = j;
            best_width_sq = width_sq;
            initialized = true;
          }
      }
 
    if (not initialized)
      return {verts(0), verts(1), verts(0), 0};
 
    return {verts(best_i), verts(best_ni), verts(best_j), best_width_sq};
  }
};
 
// ============================================================================
// Point-in-Polygon
// ============================================================================
 
class PointInPolygonWinding
{
public:
  enum class Location
  {
    Outside,
    Boundary,
    Inside
  };
 
  static Location locate(const Polygon &poly, const Point &p)
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
 
    ah_domain_error_if(poly.size() < 3) << "Point-in-polygon requires at least 3 vertices";
 
    switch (poly.locate_point(p))
      {
      case Polygon::PointLocation::Boundary:
        return Location::Boundary;
      case Polygon::PointLocation::Inside:
        return Location::Inside;
      case Polygon::PointLocation::Outside:
      default:
        return Location::Outside;
      }
  }
 
  [[nodiscard]] static bool contains(const Polygon &poly, const Point &p)
  {
    const Location loc = locate(poly, p);
    return loc != Location::Outside;
  }
 
  [[nodiscard]] static bool strictly_contains(const Polygon &poly, const Point &p)
  {
    return locate(poly, p) == Location::Inside;
  }
};
 
// ============================================================================
// Polygon Intersection (Basic)
// ============================================================================
 
class ConvexPolygonIntersectionBasic
{
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &poly)
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
 
    ah_domain_error_if(poly.size() < 3) << "Polygon must have at least 3 vertices";
 
    return GeomPolygonUtils::extract_vertices(poly);
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Array<Point> &verts)
  {
    return GeomPolygonUtils::signed_double_area(verts);
  }
 
  [[nodiscard]] static bool is_convex(const Array<Point> &verts)
  {
    if (verts.size() < 3)
      return false;
    return GeomPolygonUtils::is_convex(verts);
  }
 
  [[nodiscard]] static bool inside_half_plane(const Point &p,
                                              const Point &a,
                                              const Point &b,
                                              const bool clip_ccw)
  {
    const Orientation o = orientation(a, b, p);
    return clip_ccw ? o != Orientation::CW : o != Orientation::CCW;
  }
 
  [[nodiscard]] static Point line_intersection(const Point &s,
                                               const Point &e,
                                               const Point &a,
                                               const Point &b)
  {
    const Geom_Number rx = e.get_x() - s.get_x();
    const Geom_Number ry = e.get_y() - s.get_y();
    const Geom_Number sx = b.get_x() - a.get_x();
    const Geom_Number sy = b.get_y() - a.get_y();
 
    const Geom_Number den = rx * sy - ry * sx;
    if (den == 0)
      {
        if (orientation(a, b, s) == Orientation::COLLINEAR)
          return s;
        if (orientation(a, b, e) == Orientation::COLLINEAR)
          return e;
        return s;
      }
 
    const Geom_Number qpx = a.get_x() - s.get_x();
    const Geom_Number qpy = a.get_y() - s.get_y();
    const Geom_Number t = (qpx * sy - qpy * sx) / den;
 
    return {s.get_x() + t * rx, s.get_y() + t * ry};
  }
 
  static void push_clean(Array<Point> &out, const Point &p)
  {
    if (out.is_empty())
      {
        out.append(p);
        return;
      }
 
    if (out.get_last() == p)
      return;
 
    while (out.size() >= 2)
      {
        const Point &a = out(out.size() - 2);
        const Point &b = out(out.size() - 1);
        if (orientation(a, b, p) != Orientation::COLLINEAR)
          break;
 
        if (const Segment ab(a, b); on_segment(ab, p))
          return;
 
        static_cast<void>(out.remove_last());
      }
 
    out.append(p);
  }
 
  [[nodiscard]] static Array<Point> normalize_vertices(const Array<Point> &pts)
  {
    Array<Point> ret;
    ret.reserve(pts.size());
    for (size_t i = 0; i < pts.size(); ++i)
      push_clean(ret, pts(i));
 
    if (ret.size() > 1 and ret(0) == ret.get_last())
      static_cast<void>(ret.remove_last());
 
    return ret;
  }
 
  [[nodiscard]] static Polygon build_polygon(const Array<Point> &pts)
  {
    Polygon ret;
    Array<Point> clean = normalize_vertices(pts);
 
    for (size_t i = 0; i < clean.size(); ++i)
      ret.add_vertex(clean(i));
 
    if (ret.size() >= 3)
      ret.close();
 
    return ret;
  }
 
public:
  [[nodiscard]] Polygon operator () (const Polygon &subject, const Polygon &clip) const
  {
    const Array<Point> subj = extract_vertices(subject);
    const Array<Point> clp = extract_vertices(clip);
 
    ah_domain_error_if(not is_convex(subj)) << "Subject polygon must be convex";
    ah_domain_error_if(not is_convex(clp)) << "Clip polygon must be convex";
 
    const Geom_Number clip_area2 = signed_double_area(clp);
    ah_domain_error_if(clip_area2 == 0) << "Clip polygon is degenerate";
 
    const bool clip_ccw = clip_area2 > 0;
 
    Array<Point> output = subj;
 
    for (size_t i = 0; i < clp.size(); ++i)
      {
        if (output.is_empty())
          break;
 
        const Point &a = clp(i);
        const Point &b = clp((i + 1) % clp.size());
 
        const Array<Point> input = output;
        output = Array<Point>();
        output.reserve(input.size() + 2);
 
        Point s = input.get_last();
        bool s_inside = inside_half_plane(s, a, b, clip_ccw);
 
        for (size_t j = 0; j < input.size(); ++j)
          {
            const Point &e = input(j);
            const bool e_inside = inside_half_plane(e, a, b, clip_ccw);
 
            if (e_inside)
              {
                if (not s_inside)
                  push_clean(output, line_intersection(s, e, a, b));
                push_clean(output, e);
              }
            else if (s_inside)
              push_clean(output, line_intersection(s, e, a, b));
 
            s = e;
            s_inside = e_inside;
          }
 
        output = normalize_vertices(output);
      }
 
    return build_polygon(output);
  }
};
 
// ============================================================================
// Half-Plane Intersection
// ============================================================================
 
class HalfPlaneIntersection
{
public:
  struct HalfPlane
  {
    Point p;
    Point q;
 
    HalfPlane() = default;
 
    HalfPlane(Point p_, Point q_) : p(std::move(p_)), q(std::move(q_)) {}
 
    [[nodiscard]] Geom_Number dx() const
    {
      return q.get_x() - p.get_x();
    }
 
    [[nodiscard]] Geom_Number dy() const
    {
      return q.get_y() - p.get_y();
    }
 
    [[nodiscard]] Geom_Number offset() const
    {
      // n = (-dy, dx), inequality n.x*x + n.y*y >= offset
      return -dy() * p.get_x() + dx() * p.get_y();
    }
 
    [[nodiscard]] bool outside(const Point &x) const
    {
      return orientation(p, q, x) == Orientation::CW;
    }
  };
 
private:
  [[nodiscard]] static Geom_Number signed_double_area(const Array<Point> &verts)
  {
    return GeomPolygonUtils::signed_double_area(verts);
  }
 
  [[nodiscard]] static bool upper_half(const HalfPlane &h)
  {
    return h.dy() > 0 or h.dy() == 0 and h.dx() >= 0;
  }
 
  [[nodiscard]] static Geom_Number cross_dir(const HalfPlane &a, const HalfPlane &b)
  {
    return a.dx() * b.dy() - a.dy() * b.dx();
  }
 
  [[nodiscard]] static Geom_Number dot_dir(const HalfPlane &a, const HalfPlane &b)
  {
    return a.dx() * b.dx() + a.dy() * b.dy();
  }
 
  [[nodiscard]] static bool same_direction(const HalfPlane &a, const HalfPlane &b)
  {
    return cross_dir(a, b) == 0 and dot_dir(a, b) > 0;
  }
 
  [[nodiscard]] static bool parallel(const HalfPlane &a, const HalfPlane &b)
  {
    return cross_dir(a, b) == 0;
  }
 
  [[nodiscard]] static Point line_intersection(const HalfPlane &a, const HalfPlane &b)
  {
    const Geom_Number rx = a.dx();
    const Geom_Number ry = a.dy();
    const Geom_Number sx = b.dx();
    const Geom_Number sy = b.dy();
 
    const Geom_Number den = rx * sy - ry * sx;
    ah_domain_error_if(den == 0) << "Parallel half-plane boundaries";
 
    const Geom_Number qpx = b.p.get_x() - a.p.get_x();
    const Geom_Number qpy = b.p.get_y() - a.p.get_y();
    const Geom_Number t = (qpx * sy - qpy * sx) / den;
 
    return {a.p.get_x() + t * rx, a.p.get_y() + t * ry};
  }
 
  static void push_clean(Array<Point> &out, const Point &p)
  {
    if (out.is_empty())
      {
        out.append(p);
        return;
      }
 
    if (out.get_last() == p)
      return;
 
    while (out.size() >= 2)
      {
        const Point &a = out(out.size() - 2);
        const Point &b = out(out.size() - 1);
        if (orientation(a, b, p) != Orientation::COLLINEAR)
          break;
 
        if (const Segment ab(a, b); on_segment(ab, p))
          return;
 
        static_cast<void>(out.remove_last());
      }
 
    out.append(p);
  }
 
  [[nodiscard]] static Array<Point> normalize_vertices(const Array<Point> &pts)
  {
    Array<Point> ret;
    ret.reserve(pts.size());
    for (size_t i = 0; i < pts.size(); ++i)
      push_clean(ret, pts(i));
 
    if (ret.size() > 1 and ret(0) == ret.get_last())
      static_cast<void>(ret.remove_last());
 
    return ret;
  }
 
  [[nodiscard]] static Polygon build_polygon(const Array<Point> &pts)
  {
    Polygon ret;
    const Array<Point> clean = normalize_vertices(pts);
 
    for (size_t i = 0; i < clean.size(); ++i)
      ret.add_vertex(clean(i));
 
    if (ret.size() >= 3)
      ret.close();
 
    return ret;
  }
 
public:
  [[nodiscard]] static Array<HalfPlane> from_convex_polygon(const Polygon &poly)
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(poly.size() < 3) << "Polygon must have at least 3 vertices";
 
    Array<Point> verts;
    verts.reserve(poly.size());
    for (Polygon::Vertex_Iterator it(poly); it.has_curr(); it.next_ne())
      verts.append(it.get_current_vertex());
 
    const Geom_Number area2 = signed_double_area(verts);
    ah_domain_error_if(area2 == 0) << "Polygon is degenerate";
    const bool ccw = area2 > 0;
 
    Array<HalfPlane> hs;
    hs.reserve(verts.size());
    for (size_t i = 0; i < verts.size(); ++i)
      {
        const Point &a = verts(i);
        const Point &b = verts((i + 1) % verts.size());
        hs.append(ccw ? HalfPlane(a, b) : HalfPlane(b, a));
      }
    return hs;
  }
 
  [[nodiscard]] Polygon operator () (const Array<HalfPlane> &halfplanes) const
  {
    if (halfplanes.size() < 3)
      return {};
 
    Array<HalfPlane> hps = halfplanes;
    quicksort_op(hps, [](const HalfPlane &a, const HalfPlane &b)
      {
        const bool ha = upper_half(a);
        const bool hb = upper_half(b);
        if (ha != hb)
          return ha and not hb;
 
        if (const Geom_Number cr = cross_dir(a, b); cr != 0)
          return cr > 0;
 
        // Same direction: keep stronger constraints first.
        return a.offset() > b.offset();
      });
 
    Array<HalfPlane> unique;
    unique.reserve(hps.size());
    for (size_t i = 0; i < hps.size(); ++i)
      {
        const HalfPlane &hp = hps(i);
        if (unique.is_empty())
          {
            unique.append(hp);
            continue;
          }
 
        if (const HalfPlane &last = unique.get_last(); same_direction(last, hp))
          {
            if (hp.offset() > last.offset())
              {
                static_cast<void>(unique.remove_last());
                unique.append(hp);
              }
            continue;
          }
 
        unique.append(hp);
      }
 
    DynDlist<HalfPlane> dq;
    DynDlist<Point> intersections;
 
    for (size_t i = 0; i < unique.size(); ++i)
      {
        const HalfPlane &hp = unique(i);
 
        while (not intersections.is_empty() and hp.outside(intersections.get_last()))
          {
            dq.remove_last();
            intersections.remove_last();
          }
 
        while (not intersections.is_empty() and hp.outside(intersections.get_first()))
          {
            dq.remove_first();
            intersections.remove_first();
          }
 
        if (not dq.is_empty() and parallel(dq.get_last(), hp))
          {
            if (same_direction(dq.get_last(), hp))
              {
                if (hp.offset() > dq.get_last().offset())
                  {
                    dq.remove_last();
                    if (not intersections.is_empty())
                      intersections.remove_last();
                  }
                else
                  continue;
              }
            else  // Opposite parallel boundaries cannot define a bounded polygon here.
              return {};
          }
 
        if (not dq.is_empty())
          intersections.append(line_intersection(dq.get_last(), hp));
 
        dq.append(hp);
      }
 
    while (not intersections.is_empty() and dq.get_first().outside(intersections.get_last()))
      {
        dq.remove_last();
        intersections.remove_last();
      }
 
    while (not intersections.is_empty() and dq.get_last().outside(intersections.get_first()))
      {
        dq.remove_first();
        intersections.remove_first();
      }
 
    if (dq.size() < 3)
      return {};
 
    if (parallel(dq.get_last(), dq.get_first()))
      return {};
 
    const Point closing = line_intersection(dq.get_last(), dq.get_first());
 
    Array<Point> verts;
    verts.reserve(intersections.size() + 1);
 
    DynDlist<Point> tmp = intersections;
    while (not tmp.is_empty())
      verts.append(tmp.remove_first());
    verts.append(closing);
 
    return build_polygon(verts);
  }
 
  [[nodiscard]] Polygon operator () (const std::initializer_list<HalfPlane> il) const
  {
    Array<HalfPlane> hps;
    hps.reserve(il.size());
    for (const HalfPlane &hp : il)
      hps.append(hp);
    return (*this)(hps);
  }
};
 
// ============================================================================
// Delaunay Triangulation (Bowyer-Watson)
// ============================================================================
 
class DelaunayTriangulationBowyerWatson
{
public:
  struct IndexedTriangle
  {
    size_t i;  
    size_t j;  
    size_t k;  
  };
 
  struct Result
  {
    Array<Point> sites;                
    Array<IndexedTriangle> triangles;  
  };
 
private:
  [[nodiscard]] static bool lexicographic_less(const Point &p1, const Point &p2)
  {
    if (p1.get_x() < p2.get_x())
      return true;
    if (p2.get_x() < p1.get_x())
      return false;
    return p1.get_y() < p2.get_y();
  }
 
  [[nodiscard]] static bool all_collinear(const Array<Point> &pts)
  {
    if (pts.size() < 3)
      return true;
 
    for (size_t i = 2; i < pts.size(); ++i)
      if (orientation(pts(0), pts(1), pts(i)) != Orientation::COLLINEAR)
        return false;
 
    return true;
  }
 
  [[nodiscard]] static bool point_in_circumcircle(const Array<Point> &pts,
                                                  const size_t ia,
                                                  const size_t ib,
                                                  const size_t ic,
                                                  const size_t ip)
  {
    const Point &a = pts(ia);
    const Point &b = pts(ib);
    const Point &c = pts(ic);
    const Point &p = pts(ip);
 
    const Geom_Number det = in_circle_determinant(a, b, c, p);
 
    const Orientation o = orientation(a, b, c);
    if (o == Orientation::CCW)
      {
        if (det > 0)
          return true;
        if (det < 0)
          return false;
      }
    if (o == Orientation::CW)
      {
        if (det < 0)
          return true;
        if (det > 0)
          return false;
      }
 
    // Cocircular / degenerate tie-break for deterministic output.
    size_t max_idx = ia;
    if (ib > max_idx)
      max_idx = ib;
    if (ic > max_idx)
      max_idx = ic;
    return ip < max_idx;
  }
 
  [[nodiscard]] static Array<Point> unique_points(const DynList<Point> &point_set)
  {
    Array<Point> all;
    for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
      all.append(it.get_curr());
 
    quicksort_op(all, [](const Point &p1, const Point &p2)
      {
        return lexicographic_less(p1, p2);
      });
 
    Array<Point> ret;
    ret.reserve(all.size());
    for (size_t i = 0; i < all.size(); ++i)
      if (ret.is_empty() or ret.get_last() != all(i))
        ret.append(all(i));
 
    return ret;
  }
 
public:
  [[nodiscard]] Result operator () (const DynList<Point> &point_set) const
  {
    Result ret;
    ret.sites = unique_points(point_set);
    const size_t n = ret.sites.size();
 
    if (n < 3 or all_collinear(ret.sites))
      return ret;
 
    Array<Point> pts = ret.sites;
    ret.triangles = GeomBowyerWatsonUtils::triangulate<IndexedTriangle>(
      std::move(pts), n,
      [](const Array<Point> &all_pts, const size_t ia, const size_t ib, const size_t ic,
         const size_t ip)
      {
        return DelaunayTriangulationBowyerWatson::point_in_circumcircle(all_pts, ia, ib, ic, ip);
      });
 
    return ret;
  }
 
  [[nodiscard]] Result operator () (const std::initializer_list<Point> il) const
  {
    DynList<Point> points;
    for (const Point &p : il)
      points.append(p);
    return (*this)(points);
  }
 
  static DynList<Triangle> as_triangles(const Result &result)
  {
    DynList<Triangle> out;
    for (size_t tria_idx = 0; tria_idx < result.triangles.size(); ++tria_idx)
      {
        const auto &[i, j, k] = result.triangles(tria_idx);
        out.append(Triangle(result.sites(i), result.sites(j), result.sites(k)));
      }
    return out;
  }
};
 
// ============================================================================
// Regular Triangulation (Weighted Delaunay) — Bowyer-Watson
// ============================================================================
 
class RegularTriangulationBowyerWatson
{
public:
  struct WeightedSite
  {
    Point position;
    Geom_Number weight;
  };
 
  using IndexedTriangle = DelaunayTriangulationBowyerWatson::IndexedTriangle;
 
  struct Result
  {
    Array<WeightedSite> sites;
    Array<IndexedTriangle> triangles;
  };
 
private:
  [[nodiscard]] static bool lex_less(const Point &p1, const Point &p2)
  {
    if (p1.get_x() < p2.get_x())
      return true;
    if (p2.get_x() < p1.get_x())
      return false;
    return p1.get_y() < p2.get_y();
  }
 
  [[nodiscard]] static bool all_collinear(const Array<WeightedSite> &s)
  {
    if (s.size() < 3)
      return true;
 
    for (size_t i = 2; i < s.size(); ++i)
      if (orientation(s(0).position, s(1).position, s(i).position) != Orientation::COLLINEAR)
        return false;
 
    return true;
  }
 
  [[nodiscard]] static bool point_in_power_circle(const Array<Point> &pts,
                                                  const Array<Geom_Number> &wts,
                                                  const size_t ia,
                                                  const size_t ib,
                                                  const size_t ic,
                                                  const size_t ip)
  {
    const Point &a = pts(ia);
    const Point &b = pts(ib);
    const Point &c = pts(ic);
    const Point &p = pts(ip);
 
    const Geom_Number adx = a.get_x() - p.get_x();
    const Geom_Number ady = a.get_y() - p.get_y();
    const Geom_Number bdx = b.get_x() - p.get_x();
    const Geom_Number bdy = b.get_y() - p.get_y();
    const Geom_Number cdx = c.get_x() - p.get_x();
    const Geom_Number cdy = c.get_y() - p.get_y();
 
    const Geom_Number ad2 = adx * adx + ady * ady - wts(ia) + wts(ip);
    const Geom_Number bd2 = bdx * bdx + bdy * bdy - wts(ib) + wts(ip);
    const Geom_Number cd2 = cdx * cdx + cdy * cdy - wts(ic) + wts(ip);
 
    const Geom_Number det =
      ad2 * (bdx * cdy - bdy * cdx) - bd2 * (adx * cdy - ady * cdx) + cd2 * (adx * bdy - ady * bdx);
 
    const Orientation o = orientation(a, b, c);
    if (o == Orientation::CCW)
      {
        if (det > 0)
          return true;
        if (det < 0)
          return false;
      }
    if (o == Orientation::CW)
      {
        if (det < 0)
          return true;
        if (det > 0)
          return false;
      }
 
    // Cocircular / degenerate tie-break for deterministic output.
    size_t max_idx = ia;
    if (ib > max_idx)
      max_idx = ib;
    if (ic > max_idx)
      max_idx = ic;
    return ip < max_idx;
  }
 
  [[nodiscard]] static Array<WeightedSite> unique_sites(const Array<WeightedSite> &input)
  {
    Array<WeightedSite> all;
    all.reserve(input.size());
    for (size_t i = 0; i < input.size(); ++i)
      all.append(input(i));
 
    quicksort_op(all, [](const WeightedSite &a, const WeightedSite &b)
      {
        return lex_less(a.position, b.position);
      });
 
    Array<WeightedSite> ret;
    ret.reserve(all.size());
    for (size_t i = 0; i < all.size(); ++i)
      if (ret.is_empty() or ret.get_last().position != all(i).position)
        ret.append(all(i));
 
    return ret;
  }
 
public:
  [[nodiscard]] Result operator () (const Array<WeightedSite> &weighted_sites) const
  {
    Result ret;
    ret.sites = unique_sites(weighted_sites);
    const size_t n = ret.sites.size();
 
    if (n < 3 or all_collinear(ret.sites))
      return ret;
 
    Array<Point> pts;
    Array<Geom_Number> wts;
    pts.reserve(n + 3);
    wts.reserve(n + 3);
    for (size_t i = 0; i < n; ++i)
      {
        pts.append(ret.sites(i).position);
        wts.append(ret.sites(i).weight);
      }
    wts.append(Geom_Number(0));
    wts.append(Geom_Number(0));
    wts.append(Geom_Number(0));
    ret.triangles = GeomBowyerWatsonUtils::triangulate<IndexedTriangle>(
      std::move(pts), n,
      [&wts](const Array<Point> &all_pts, const size_t ia, const size_t ib, const size_t ic,
             const size_t ip)
      {
        return RegularTriangulationBowyerWatson::point_in_power_circle(all_pts, wts, ia, ib, ic, ip);
      });
 
    return ret;
  }
};
 
// ============================================================================
// Delaunay Triangulation — Randomized Incremental O(n log n) expected
// ============================================================================
 
class DelaunayTriangulationRandomizedIncremental
{
public:
  using IndexedTriangle = DelaunayTriangulationBowyerWatson::IndexedTriangle;
  using Result = DelaunayTriangulationBowyerWatson::Result;
 
private:
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  struct Tri
  {
    size_t v[3];    
    size_t adj[3];  
    bool alive;
  };
 
  struct DagNode
  {
    size_t tri;
    Array<size_t> children;
  };
 
  [[nodiscard]] static size_t local_of(const Tri &t, const size_t id)
  {
    for (int i = 0; i < 3; ++i)
      if (t.v[i] == id)
        return static_cast<size_t>(i);
    return NONE;
  }
 
  [[nodiscard]] static size_t adj_of(const Tri &t, const size_t n)
  {
    for (int i = 0; i < 3; ++i)
      if (t.adj[i] == n)
        return static_cast<size_t>(i);
    return NONE;
  }
 
  [[nodiscard]] static bool point_in_tri(const Array<Point> &pts, const Tri &t, const size_t pidx)
  {
    const Orientation o0 = orientation(pts(t.v[0]), pts(t.v[1]), pts(pidx));
    const Orientation o1 = orientation(pts(t.v[1]), pts(t.v[2]), pts(pidx));
    const Orientation o2 = orientation(pts(t.v[2]), pts(t.v[0]), pts(pidx));
    const bool has_cw = o0 == Orientation::CW or o1 == Orientation::CW or o2 == Orientation::CW;
    const bool has_ccw = o0 == Orientation::CCW or o1 == Orientation::CCW or o2 == Orientation::CCW;
    return not (has_cw and has_ccw);
  }
 
  [[nodiscard]] static bool in_cc(const Array<Point> &pts,
                                  const size_t ia,
                                  const size_t ib,
                                  const size_t ic,
                                  const size_t ip)
  {
    const Geom_Number det = in_circle_determinant(pts(ia), pts(ib), pts(ic), pts(ip));
    const Orientation o = orientation(pts(ia), pts(ib), pts(ic));
    if (o == Orientation::CCW)
      {
        if (det > 0)
          return true;
        if (det < 0)
          return false;
      }
    if (o == Orientation::CW)
      {
        if (det < 0)
          return true;
        if (det > 0)
          return false;
      }
    size_t mx = ia;
    if (ib > mx)
      mx = ib;
    if (ic > mx)
      mx = ic;
    return ip < mx;
  }
 
  [[nodiscard]] static size_t locate(const Array<Point> &pts,
                                     const Array<Tri> &tris,
                                     const Array<DagNode> &dag,
                                     const size_t pidx,
                                     const size_t root)
  {
    size_t cur = root;
    while (not dag(cur).children.is_empty())
      {
        bool found = false;
        for (size_t c = 0; c < dag(cur).children.size(); ++c)
          {
            if (const size_t child = dag(cur).children(c); point_in_tri(pts, tris(child), pidx))
              {
                cur = child;
                found = true;
                break;
              }
          }
        if (not found)
          break;
      }
    return cur;
  }
 
  static void remap_adj(Array<Tri> &tris, const size_t ot, const size_t nt)
  {
    for (const unsigned long nb : tris(ot).adj)
      {
        if (nb == NONE)
          continue;
        if (const size_t li = adj_of(tris(nb), ot); li != NONE)
          tris(nb).adj[li] = nt;
      }
  }
 
public:
  [[nodiscard]] Result operator () (const DynList<Point> &point_set) const
  {
    Result ret;
 
    // Build unique sorted points.
    {
      Array<Point> all;
      for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
        all.append(it.get_curr());
      quicksort_op(all, [](const Point &a, const Point &b)
        {
          return a.get_x() < b.get_x() or (a.get_x() == b.get_x() and a.get_y() < b.get_y());
        });
      ret.sites = Array<Point>();
      ret.sites.reserve(all.size());
      for (size_t i = 0; i < all.size(); ++i)
        if (ret.sites.is_empty() or ret.sites.get_last() != all(i))
          ret.sites.append(all(i));
    }
 
    const size_t n = ret.sites.size();
    if (n < 3)
      return ret;
 
    // Check all-collinear.
    {
      bool collinear = true;
      for (size_t i = 2; i < n and collinear; ++i)
        if (orientation(ret.sites(0), ret.sites(1), ret.sites(i)) != Orientation::COLLINEAR)
          collinear = false;
      if (collinear)
        return ret;
    }
 
    // Build pts array with super-triangle appended.
    Array<Point> pts = ret.sites;
    Geom_Number mnx = pts(0).get_x(), mxx = mnx;
    Geom_Number mny = pts(0).get_y(), mxy = mny;
    for (size_t i = 1; i < n; ++i)
      {
        if (pts(i).get_x() < mnx)
          mnx = pts(i).get_x();
        if (pts(i).get_x() > mxx)
          mxx = pts(i).get_x();
        if (pts(i).get_y() < mny)
          mny = pts(i).get_y();
        if (pts(i).get_y() > mxy)
          mxy = pts(i).get_y();
      }
    Geom_Number delta = mxx - mnx > mxy - mny ? mxx - mnx : mxy - mny;
    if (delta == 0)
      delta = 1;
    const Geom_Number sp = delta * 16 + 1;
    const Geom_Number cx = (mnx + mxx) / 2, cy = (mny + mxy) / 2;
    pts.append(Point(cx - sp - sp, cy - sp));
    pts.append(Point(cx + sp + sp, cy - sp));
    pts.append(Point(cx, cy + sp + sp));
 
    // Random insertion order for input points [0..n).
    Array<size_t> order;
    order.reserve(n);
    for (size_t i = 0; i < n; ++i)
      order.append(i);
    // Fisher-Yates shuffle.
    {
      std::random_device rd;
      std::mt19937 gen(rd());
      for (size_t i = n - 1; i > 0; --i)
        {
          std::uniform_int_distribution<size_t> dis(0, i);
          const size_t j = dis(gen);
          const size_t tmp = order(i);
          order(i) = order(j);
          order(j) = tmp;
        }
    }
 
    // Initialize with super-triangle.
    Array<Tri> tris;
    Array<DagNode> dag;
    tris.append(Tri{{n, n + 1, n + 2}, {NONE, NONE, NONE}, true});
    dag.append(DagNode{0, Array<size_t>()});
 
    // Insert each point using the local Bowyer-Watson cavity approach.
    // 1) Locate containing triangle via DAG  — O(log n) expected.
    // 2) BFS from it to find all "bad" triangles (circumcircle
    //    contains the new point).
    // 3) Extract the boundary polygon of the cavity.
    // 4) Re-triangulate cavity by connecting boundary edges to
    //    the new point.
    // Expected cavity size is O(1) for random insertion order,
    // giving O(n log n) total expected time.
    for (size_t oi = 0; oi < n; ++oi)
      {
        const size_t pidx = order(oi);
        const size_t ti = locate(pts, tris, dag, pidx, 0);
 
        // --- BFS to find the cavity ---
        const size_t ntris_before = tris.size();
        Array<bool> is_bad;
        is_bad.reserve(ntris_before);
        for (size_t i = 0; i < ntris_before; ++i)
          is_bad.append(false);
 
        Array<size_t> cavity;
        is_bad(ti) = true;
        cavity.append(ti);
 
        // Frontier queue: at most one enqueue per triangle.
        FixedQueue<size_t> frontier(ntris_before + 1);
        frontier.put(ti);
        while (not frontier.is_empty())
          for (const size_t ct = frontier.get(); unsigned long nb : tris(ct).adj)
            {
              if (nb == NONE or nb >= ntris_before or not tris(nb).alive or is_bad(nb))
                continue;
              if (in_cc(pts, tris(nb).v[0], tris(nb).v[1], tris(nb).v[2], pidx))
                {
                  is_bad(nb) = true;
                  cavity.append(nb);
                  frontier.put(nb);
                }
            }
 
        // --- Extract boundary edges ---
        // Each boundary edge is an edge of a cavity triangle whose
        // neighbor is outside the cavity (or NONE).
        struct BEdge
        {
          size_t u, v, ext, old_ct;
        };
        Array<BEdge> boundary;
        for (size_t ci = 0; ci < cavity.size(); ++ci)
          {
            const size_t ct = cavity(ci);
            for (int e = 0; e < 3; ++e)
              {
                const size_t nb = tris(ct).adj[e];
                if (nb != NONE and nb < ntris_before and is_bad(nb))
                  continue;  // internal cavity edge — skip
                // Boundary edge opposite v[e]: vertices (v[(e+1)%3], v[(e+2)%3]).
                boundary.append(BEdge{tris(ct).v[(e + 1) % 3], tris(ct).v[(e + 2) % 3], nb, ct});
              }
          }
 
        // --- Create new triangles ---
        // For each boundary edge (u,v) create triangle (u, v, pidx).
        // adj[2] (opposite pidx) = external neighbor.
        const size_t V = pts.size();
        Array<size_t> as_u, as_v;  // vertex → new tri where it's u / v
        as_u.reserve(V);
        as_v.reserve(V);
        for (size_t i = 0; i < V; ++i)
          {
            as_u.append(NONE);
            as_v.append(NONE);
          }
 
        Array<size_t> new_tris;
        new_tris.reserve(boundary.size());
 
        for (size_t bi = 0; bi < boundary.size(); ++bi)
          {
            size_t u = boundary(bi).u, v = boundary(bi).v;
            const size_t ext = boundary(bi).ext;
            const size_t old_ct = boundary(bi).old_ct;
 
            // Ensure CCW winding.
            if (orientation(pts(u), pts(v), pts(pidx)) != Orientation::CCW)
              {
                const size_t tmp = u;
                u = v;
                v = tmp;
              }
 
            const size_t nt = tris.size();
            tris.append(Tri{{u, v, pidx}, {NONE, NONE, ext}, true});
            dag.append(DagNode{nt, Array<size_t>()});
            new_tris.append(nt);
 
            as_u(u) = nt;
            as_v(v) = nt;
 
            // Remap external neighbor to point to the new triangle.
            if (ext != NONE)
              if (const size_t li = adj_of(tris(ext), old_ct); li != NONE)
                tris(ext).adj[li] = nt;
          }
 
        // --- Internal adjacencies between new triangles ---
        // Two new triangles share an edge through pidx.
        // For triangle (u, v, pidx):
        //   adj[0] opp u = edge(v, pidx)  → the new tri with v as u
        //   adj[1] opp v = edge(pidx, u)  → the new tri with u as v
        for (size_t ni = 0; ni < new_tris.size(); ++ni)
          {
            const size_t nt = new_tris(ni);
            const size_t u = tris(nt).v[0];
            const size_t v = tris(nt).v[1];
            tris(nt).adj[0] = as_u(v);  // neighbor across (v, pidx)
            tris(nt).adj[1] = as_v(u);  // neighbor across (pidx, u)
          }
 
        // --- Kill cavity and update DAG ---
        for (size_t ci = 0; ci < cavity.size(); ++ci)
          {
            tris(cavity(ci)).alive = false;
            for (size_t ni = 0; ni < new_tris.size(); ++ni)
              dag(cavity(ci)).children.append(new_tris(ni));
          }
      }
 
    // Collect alive triangles that don't reference super-triangle.
    ret.triangles.reserve(2 * n);
    for (size_t t = 0; t < tris.size(); ++t)
      {
        const Tri &tr = tris(t);
        if (not tr.alive)
          continue;
        if (tr.v[0] >= n or tr.v[1] >= n or tr.v[2] >= n)
          continue;
        if (orientation(pts(tr.v[0]), pts(tr.v[1]), pts(tr.v[2])) == Orientation::COLLINEAR)
          continue;
        ret.triangles.append(IndexedTriangle{tr.v[0], tr.v[1], tr.v[2]});
      }
 
    return ret;
  }
 
  [[nodiscard]] Result operator () (const std::initializer_list<Point> il) const
  {
    DynList<Point> points;
    for (const Point &p : il)
      points.append(p);
    return (*this)(points);
  }
};
 
// ============================================================================
// Constrained Delaunay Triangulation (CDT)
// ============================================================================
 
class ConstrainedDelaunayTriangulation
{
public:
  using IndexedTriangle = DelaunayTriangulationBowyerWatson::IndexedTriangle;
 
  struct IndexedEdge
  {
    size_t u;
    size_t v;
  };
 
  struct Result
  {
    Array<Point> sites;
    Array<IndexedTriangle> triangles;
    Array<IndexedEdge> constrained_edges;
  };
 
private:
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  struct Tri
  {
    size_t v[3];          
    size_t adj[3];        
    bool constrained[3];  
    bool alive;
  };
 
  [[nodiscard]] static bool lexicographic_less(const Point &p1, const Point &p2)
  {
    if (p1.get_x() < p2.get_x())
      return true;
    if (p2.get_x() < p1.get_x())
      return false;
    return p1.get_y() < p2.get_y();
  }
 
  [[nodiscard]] static size_t find_point_index(const Array<Point> &pts, const Point &p)
  {
    size_t lo = 0, hi = pts.size();
    while (lo < hi)
      if (const size_t mid = lo + (hi - lo) / 2; lexicographic_less(pts(mid), p))
        lo = mid + 1;
      else if (lexicographic_less(p, pts(mid)))
        hi = mid;
      else
        return mid;
    return NONE;
  }
 
  [[nodiscard]] static size_t local_of(const Tri &t, const size_t id)
  {
    for (int i = 0; i < 3; ++i)
      if (t.v[i] == id)
        return static_cast<size_t>(i);
    return NONE;
  }
 
  [[nodiscard]] static size_t adj_of(const Tri &t, const size_t n)
  {
    for (int i = 0; i < 3; ++i)
      if (t.adj[i] == n)
        return static_cast<size_t>(i);
    return NONE;
  }
 
  [[nodiscard]] static size_t edge_opposite(const Tri &t, const size_t a, const size_t b)
  {
    for (int i = 0; i < 3; ++i)
      {
        const size_t e0 = t.v[(i + 1) % 3];
        const size_t e1 = t.v[(i + 2) % 3];
        if ((e0 == a and e1 == b) or (e0 == b and e1 == a))
          return static_cast<size_t>(i);
      }
    return NONE;
  }
 
  static void build_adjacency(Array<Tri> &tris, const Array<IndexedTriangle> &dt_tris)
  {
    tris.reserve(dt_tris.size());
    for (size_t i = 0; i < dt_tris.size(); ++i)
      {
        const auto &t = dt_tris(i);
        tris.append(Tri{{t.i, t.j, t.k}, {NONE, NONE, NONE}, {false, false, false}, true});
      }
 
    GeomTriangleAdjacencyUtils::for_each_sorted_edge_group(
      dt_tris,
      [&](const Array<GeomTriangleAdjacencyUtils::EdgeRef> &edges, const size_t first,
          const size_t last)
      {
        if (last - first != 2)
          return;  // boundary edge (1 tri) or degenerate
 
        const auto &e0 = edges(first);
        const auto &e1 = edges(first + 1);
 
        const size_t t0 = e0.tri;
        const size_t t1 = e1.tri;
        const size_t loc0 = edge_opposite(tris(t0), e0.u, e0.v);
        const size_t loc1 = edge_opposite(tris(t1), e1.u, e1.v);
 
        if (loc0 != NONE)
          tris(t0).adj[loc0] = t1;
        if (loc1 != NONE)
          tris(t1).adj[loc1] = t0;
      });
  }
 
  [[nodiscard]] static bool edge_exists(const Array<Tri> &tris,
                                        const size_t u,
                                        const size_t v,
                                        size_t &out_tri,
                                        size_t &out_local)
  {
    for (size_t t = 0; t < tris.size(); ++t)
      {
        if (not tris(t).alive)
          continue;
 
        if (const size_t loc = edge_opposite(tris(t), u, v); loc != NONE)
          {
            out_tri = t;
            out_local = loc;
            return true;
          }
      }
    return false;
  }
 
  [[nodiscard]] static bool is_convex_quad(const Array<Point> &pts,
                                           const size_t a,
                                           const size_t b,
                                           const size_t c,
                                           const size_t d)
  {
    const Orientation o1 = orientation(pts(a), pts(d), pts(b));
    const Orientation o2 = orientation(pts(a), pts(d), pts(c));
    if (o1 == Orientation::COLLINEAR or o2 == Orientation::COLLINEAR)
      return false;
    if (o1 == o2)
      return false;
 
    const Orientation o3 = orientation(pts(b), pts(c), pts(a));
    const Orientation o4 = orientation(pts(b), pts(c), pts(d));
    if (o3 == Orientation::COLLINEAR or o4 == Orientation::COLLINEAR)
      return false;
    if (o3 == o4)
      return false;
 
    return true;
  }
 
  static void flip_edge(Array<Tri> &tris, const size_t tri_a, const size_t tri_b)
  {
    Tri &ta = tris(tri_a);
    Tri &tb = tris(tri_b);
 
    // Identify the shared edge.
    const size_t la = adj_of(ta, tri_b);
    const size_t lb = adj_of(tb, tri_a);
    if (la == NONE or lb == NONE)
      return;
 
    // Vertices: a_opp is opposite the shared edge in ta,
    //           b_opp is opposite the shared edge in tb.
    const size_t a_opp = ta.v[la];
    const size_t b_opp = tb.v[lb];
    const size_t p = ta.v[(la + 1) % 3];  // shared edge start
    const size_t q = ta.v[(la + 2) % 3];  // shared edge end
 
    // External neighbors before the flip.
    const size_t ext_a1 = ta.adj[(la + 1) % 3];  // neighbor opp p in ta
    const size_t ext_a2 = ta.adj[(la + 2) % 3];  // neighbor opp q in ta
    const size_t ext_b1 = tb.adj[(lb + 1) % 3];  // neighbor opp p_adj in tb
    const size_t ext_b2 = tb.adj[(lb + 2) % 3];  // neighbor opp q_adj in tb
 
    // Constrained flags for external edges.
    const bool con_a1 = ta.constrained[(la + 1) % 3];
    const bool con_a2 = ta.constrained[(la + 2) % 3];
    const bool con_b1 = tb.constrained[(lb + 1) % 3];
    const bool con_b2 = tb.constrained[(lb + 2) % 3];
 
    // Identify which external neighbors of tb go with which new triangle.
    // tb has vertices: b_opp, p', q' where p' = tb.v[(lb+1)%3], q' = tb.v[(lb+2)%3]
    // p' and q' are p and q (in some order).
    const size_t bp = tb.v[(lb + 1) % 3];  // one of {p, q}
    const size_t bq = tb.v[(lb + 2) % 3];  // the other
 
    // New triangle A: (a_opp, b_opp, q) — uses new diagonal + edge (b_opp, q)
    // New triangle B: (b_opp, a_opp, p) — uses new diagonal + edge (a_opp, p)
    // Ensure CCW winding.
 
    // After flip, new triangles share edge (a_opp, b_opp).
    // tri_a becomes (a_opp, b_opp, q) [CCW if original was CCW]
    // tri_b becomes (b_opp, a_opp, p) [CCW if original was CCW]
 
    // New tri_a = (a_opp, b_opp, q):
    //   - adj[0] opp a_opp = edge(b_opp, q) — this was in tb between b_opp and q
    //   - adj[1] opp b_opp = edge(q, a_opp) — this was in ta between q and a_opp
    //   - adj[2] opp q     = tri_b (new diagonal)
    // New tri_b = (b_opp, a_opp, p):
    //   - adj[0] opp b_opp = edge(a_opp, p) — this was in ta between a_opp and p
    //   - adj[1] opp a_opp = edge(p, b_opp) — this was in tb between p and b_opp
    //   - adj[2] opp p     = tri_a (new diagonal)
 
    // Figure out external neighbors and constrained flags.
    // From ta: edge opp (la+1)%3 i.e., opp ta.v[(la+1)%3] = opp p = edge(a_opp, q)
    //          edge opp (la+2)%3 i.e., opp ta.v[(la+2)%3] = opp q = edge(p, a_opp)
    // So: ext_a1 is neighbor across edge(a_opp, q), ext_a2 across edge(p, a_opp).
    //
    // From tb: bp = tb.v[(lb+1)%3], bq = tb.v[(lb+2)%3]
    //          ext_b1 is neighbor across edge(b_opp, bq), opp bp
    //          ext_b2 is neighbor across edge(bp, b_opp), opp bq
 
    // New tri_a = (a_opp, b_opp, q):
    //   adj[0] opp a_opp = edge(b_opp, q): this is from tb. If bq==q, ext_b1; if bp==q, ext_b2
    //   adj[1] opp b_opp = edge(q, a_opp): this is ext_a1
    //   adj[2] opp q = tri_b
    size_t new_a_adj0;
    bool new_a_con0;
 
    const size_t new_a_adj1 = ext_a1;  // edge(q, a_opp) was opp p in ta
    const bool new_a_con1 = con_a1;
    const size_t new_a_adj2 = tri_b;
    constexpr bool new_a_con2 = false;  // the new diagonal is not constrained
 
    if (bq == q)
      {
        new_a_adj0 = ext_b1;  // edge(b_opp, q) was opp bp in tb
        new_a_con0 = con_b1;
      }
    else
      {
        new_a_adj0 = ext_b2;  // edge(b_opp, q) was opp bq in tb, so bp==q
        new_a_con0 = con_b2;
      }
 
    // New tri_b = (b_opp, a_opp, p):
    //   adj[0] opp b_opp = edge(a_opp, p): this is ext_a2
    //   adj[1] opp a_opp = edge(p, b_opp): from tb. If bp==p, ext_b2; if bq==p, ext_b1
    //   adj[2] opp p = tri_a
    size_t new_b_adj1;
    bool new_b_con1;
 
    const size_t new_b_adj0 = ext_a2;  // edge(p, a_opp) was opp q in ta
    const bool new_b_con0 = con_a2;
    const size_t new_b_adj2 = tri_a;
    constexpr bool new_b_con2 = false;  // new diagonal
 
    if (bp == p)
      {
        new_b_adj1 = ext_b2;  // edge(p, b_opp) was opp bq in tb
        new_b_con1 = con_b2;
      }
    else
      {
        new_b_adj1 = ext_b1;  // edge(p, b_opp) was opp bp in tb, bq==p
        new_b_con1 = con_b1;
      }
 
    // Write new triangles.
    ta.v[0] = a_opp;
    ta.v[1] = b_opp;
    ta.v[2] = q;
    ta.adj[0] = new_a_adj0;
    ta.adj[1] = new_a_adj1;
    ta.adj[2] = new_a_adj2;
    ta.constrained[0] = new_a_con0;
    ta.constrained[1] = new_a_con1;
    ta.constrained[2] = new_a_con2;
 
    tb.v[0] = b_opp;
    tb.v[1] = a_opp;
    tb.v[2] = p;
    tb.adj[0] = new_b_adj0;
    tb.adj[1] = new_b_adj1;
    tb.adj[2] = new_b_adj2;
    tb.constrained[0] = new_b_con0;
    tb.constrained[1] = new_b_con1;
    tb.constrained[2] = new_b_con2;
 
    // Remap external neighbors to point to correct new triangle.
    if (new_a_adj0 != NONE)
      if (const size_t li = adj_of(tris(new_a_adj0), tri_b); li != NONE)
        tris(new_a_adj0).adj[li] = tri_a;
    if (new_b_adj0 != NONE)
      if (const size_t li = adj_of(tris(new_b_adj0), tri_a); li != NONE)
        tris(new_b_adj0).adj[li] = tri_b;
    if (new_b_adj1 != NONE)
      if (const size_t li = adj_of(tris(new_b_adj1), tri_a); li != NONE)
        tris(new_b_adj1).adj[li] = tri_b;
    if (new_a_adj1 != NONE)
      if (const size_t li = adj_of(tris(new_a_adj1), tri_b); li != NONE)
        tris(new_a_adj1).adj[li] = tri_a;
  }
 
  struct CrossingEdge
  {
    size_t tri;
    size_t local;  
  };
 
  [[nodiscard]] static Array<CrossingEdge> find_crossing_edges(const Array<Point> &pts,
                                                               const Array<Tri> &tris,
                                                               const size_t u,
                                                               const size_t v)
  {
    Array<CrossingEdge> crossings;
    const Segment seg_uv(pts(u), pts(v));
 
    for (size_t t = 0; t < tris.size(); ++t)
      {
        if (not tris(t).alive)
          continue;
 
        for (int e = 0; e < 3; ++e)
          {
            const size_t w1 = tris(t).v[(e + 1) % 3];
            const size_t w2 = tris(t).v[(e + 2) % 3];
 
            // Skip edges incident to u or v (they can't "cross").
            if (w1 == u or w1 == v or w2 == u or w2 == v)
              continue;
 
            // Only process each undirected edge once (from the triangle
            // with the smaller index, or from the boundary side).
            const size_t nb = tris(t).adj[e];
            if (nb != NONE and nb < t)
              continue;
 
            if (const Segment seg_edge(pts(w1), pts(w2)); seg_uv.intersects_properly_with(seg_edge))
              {
                crossings.append(CrossingEdge{t, static_cast<size_t>(e)});
                // Also record from the neighbor's side.
                if (nb != NONE and tris(nb).alive)
                  if (const size_t lb = adj_of(tris(nb), t); lb != NONE)
                    crossings.append(CrossingEdge{nb, lb});
              }
          }
      }
 
    return crossings;
  }
 
  static void mark_constrained(Array<Tri> &tris, const size_t u, const size_t v)
  {
    for (size_t t = 0; t < tris.size(); ++t)
      {
        if (not tris(t).alive)
          continue;
 
        if (const size_t loc = edge_opposite(tris(t), u, v); loc != NONE)
          tris(t).constrained[loc] = true;
      }
  }
 
  static void enforce_constraint(Array<Point> &pts, Array<Tri> &tris, const size_t u, const size_t v)
  {
    // Check if edge already in mesh.
    size_t et, el;
    if (edge_exists(tris, u, v, et, el))
      {
        mark_constrained(tris, u, v);
        return;
      }
 
    // Find crossing edges and flip them.
    const size_t max_iterations = tris.size() * 4 + 100;
    for (size_t iter = 0; iter < max_iterations; ++iter)
      {
        // Check if the edge now exists.
        if (edge_exists(tris, u, v, et, el))
          {
            mark_constrained(tris, u, v);
            return;
          }
 
        Array<CrossingEdge> crossings = find_crossing_edges(pts, tris, u, v);
        if (crossings.is_empty())
          {
            // Edge should exist now, or no crossings found.
            if (edge_exists(tris, u, v, et, el))
              mark_constrained(tris, u, v);
            return;
          }
 
        bool flipped_any = false;
        for (size_t ci = 0; ci < crossings.size(); ++ci)
          {
            const size_t tri_idx = crossings(ci).tri;
            const size_t loc_idx = crossings(ci).local;
 
            if (not tris(tri_idx).alive)
              continue;
 
            if (tris(tri_idx).constrained[loc_idx])
              continue;  // don't flip constrained edges
 
            const size_t nb = tris(tri_idx).adj[loc_idx];
            if (nb == NONE or not tris(nb).alive)
              continue;
 
            // Get the four vertices of the quadrilateral.
            const size_t a = tris(tri_idx).v[loc_idx];  // opposite vertex in tri_idx
            const size_t lb = adj_of(tris(nb), tri_idx);
            if (lb == NONE)
              continue;
            const size_t d = tris(nb).v[lb];  // opposite vertex in nb
            const size_t b = tris(tri_idx).v[(loc_idx + 1) % 3];
            const size_t c = tris(tri_idx).v[(loc_idx + 2) % 3];
 
            if (is_convex_quad(pts, a, b, c, d))
              {
                flip_edge(tris, tri_idx, nb);
                flipped_any = true;
                break;  // restart since crossings changed
              }
          }
 
        if (not flipped_any)
          {
            // Try flipping any crossing edge even non-convex (won't flip but
            // we break infinite loop).
            break;
          }
      }
 
    // Final check — mark if the edge appeared.
    if (edge_exists(tris, u, v, et, el))
      mark_constrained(tris, u, v);
  }
 
  static void lawson_flip(const Array<Point> &pts, Array<Tri> &tris)
  {
    // Collect all non-constrained interior edges.
    // Use a simple iterative approach: keep flipping until no more flips.
    bool changed = true;
    const size_t max_passes = tris.size() * 4 + 100;
    size_t pass = 0;
 
    while (changed and pass++ < max_passes)
      {
        changed = false;
 
        for (size_t t = 0; t < tris.size(); ++t)
          {
            if (not tris(t).alive)
              continue;
 
            for (int e = 0; e < 3; ++e)
              {
                if (tris(t).constrained[e])
                  continue;  // don't flip constrained edges
 
                const size_t nb = tris(t).adj[e];
                if (nb == NONE or nb <= t)  // process each pair once
                  continue;
                if (not tris(nb).alive)
                  continue;
 
                // in-circle test: is the opposite vertex of nb inside
                // the circumcircle of t?
                const size_t lb = adj_of(tris(nb), t);
                if (lb == NONE)
                  continue;
 
                const size_t d = tris(nb).v[lb];  // opposite vertex in nb
 
                // Check CCW orientation of triangle t
                const Orientation o =
                  orientation(pts(tris(t).v[0]), pts(tris(t).v[1]), pts(tris(t).v[2]));
                if (o == Orientation::COLLINEAR)
                  continue;
 
                const Geom_Number det = in_circle_determinant(pts(tris(t).v[0]), pts(tris(t).v[1]),
                                                              pts(tris(t).v[2]), pts(d));
 
                bool violates = false;
                if (o == Orientation::CCW and det > 0)
                  violates = true;
                else if (o == Orientation::CW and det < 0)
                  violates = true;
 
                if (not violates)
                  continue;
 
                // Check convexity before flipping.
                const size_t a = tris(t).v[e];
                const size_t b = tris(t).v[(e + 1) % 3];
                const size_t c = tris(t).v[(e + 2) % 3];
 
                if (is_convex_quad(pts, a, b, c, d))
                  {
                    flip_edge(tris, t, nb);
                    changed = true;
                  }
              }
          }
      }
  }
 
  [[nodiscard]] static Array<Point> merge_and_deduplicate(const DynList<Point> &points,
                                                          const DynList<Segment> &constraints)
  {
    Array<Point> all;
    for (DynList<Point>::Iterator it(points); it.has_curr(); it.next_ne())
      all.append(it.get_curr());
 
    // Collect constraint segments into an array for pairwise checks.
    Array<Segment> con_arr;
    for (DynList<Segment>::Iterator it(constraints); it.has_curr(); it.next_ne())
      {
        const Segment &s = it.get_curr();
        all.append(s.get_src_point());
        all.append(s.get_tgt_point());
        con_arr.append(s);
      }
 
    // Compute pairwise intersection points of constraints.
    for (size_t i = 0; i < con_arr.size(); ++i)
      for (size_t j = i + 1; j < con_arr.size(); ++j)
        if (con_arr(i).intersects_properly_with(con_arr(j)))
          all.append(segment_intersection_point(con_arr(i), con_arr(j)));
 
    quicksort_op(all, [](const Point &a, const Point &b)
      {
        return lexicographic_less(a, b);
      });
 
    Array<Point> ret;
    ret.reserve(all.size());
    for (size_t i = 0; i < all.size(); ++i)
      if (ret.is_empty() or ret.get_last() != all(i))
        ret.append(all(i));
 
    return ret;
  }
 
  [[nodiscard]] static Array<IndexedEdge> map_constraints(const Array<Point> &sites,
                                                          const DynList<Segment> &constraints)
  {
    Array<IndexedEdge> result;
 
    for (DynList<Segment>::Iterator it(constraints); it.has_curr(); it.next_ne())
      {
        const Segment &seg = it.get_curr();
        const size_t u = find_point_index(sites, seg.get_src_point());
        const size_t v = find_point_index(sites, seg.get_tgt_point());
 
        if (u == NONE or v == NONE or u == v)
          continue;
 
        // Find interior collinear points and split.
        Array<size_t> chain;
        chain.append(u);
        for (size_t i = 0; i < sites.size(); ++i)
          {
            if (i == u or i == v)
              continue;
            if (seg.contains(sites(i)))
              chain.append(i);
          }
        chain.append(v);
 
        // Sort chain by distance from u.
        if (chain.size() > 2)
          {
            const Point &pu = sites(u);
            quicksort_op(chain, [&](const size_t a, const size_t b)
              {
                const Geom_Number da =
                  (sites(a).get_x() - pu.get_x()) * (sites(a).get_x() - pu.get_x()) +
                  (sites(a).get_y() - pu.get_y()) * (sites(a).get_y() - pu.get_y());
                const Geom_Number db =
                  (sites(b).get_x() - pu.get_x()) * (sites(b).get_x() - pu.get_x()) +
                  (sites(b).get_y() - pu.get_y()) * (sites(b).get_y() - pu.get_y());
                return da < db;
              });
          }
 
        for (size_t i = 0; i + 1 < chain.size(); ++i)
          {
            const size_t a = chain(i) < chain(i + 1) ? chain(i) : chain(i + 1);
            const size_t b = chain(i) < chain(i + 1) ? chain(i + 1) : chain(i);
            // Avoid duplicates.
            bool dup = false;
            for (size_t j = 0; j < result.size(); ++j)
              if (result(j).u == a and result(j).v == b)
                {
                  dup = true;
                  break;
                }
            if (not dup)
              result.append(IndexedEdge{a, b});
          }
      }
 
    return result;
  }
 
public:
  [[nodiscard]] Result operator () (const DynList<Point> &points,
                                    const DynList<Segment> &constraints) const
  {
    Result ret;
 
    // 1. Merge and deduplicate.
    ret.sites = merge_and_deduplicate(points, constraints);
    const size_t n = ret.sites.size();
 
    if (n < 3)
      return ret;
 
    // Check all-collinear.
    {
      bool collinear = true;
      for (size_t i = 2; i < n and collinear; ++i)
        if (orientation(ret.sites(0), ret.sites(1), ret.sites(i)) != Orientation::COLLINEAR)
          collinear = false;
      if (collinear)
        return ret;
    }
 
    // 2. Compute unconstrained DT.
    DynList<Point> site_list;
    for (size_t i = 0; i < n; ++i)
      site_list.append(ret.sites(i));
 
    constexpr DelaunayTriangulationBowyerWatson dt_algo;
    auto [sites, triangles] = dt_algo(site_list);
 
    if (triangles.is_empty())
      return ret;
 
    // The DT may have reordered sites. We need to use its sites array
    // and remap. Since both are sorted/deduped, they should match.
    ret.sites = sites;
 
    // 3. Build adjacency mesh.
    Array<Tri> tris;
    build_adjacency(tris, triangles);
 
    // 4. Map constraints to index pairs (with splitting).
    Array<IndexedEdge> indexed_constraints = map_constraints(ret.sites, constraints);
 
    // 5. Enforce each constraint.
    for (size_t i = 0; i < indexed_constraints.size(); ++i)
      enforce_constraint(ret.sites, tris, indexed_constraints(i).u, indexed_constraints(i).v);
 
    // 6. Lawson flip pass.
    lawson_flip(ret.sites, tris);
 
    // 7. Extract result.
    ret.triangles.reserve(tris.size());
    for (size_t t = 0; t < tris.size(); ++t)
      {
        if (not tris(t).alive)
          continue;
        if (orientation(ret.sites(tris(t).v[0]), ret.sites(tris(t).v[1]), ret.sites(tris(t).v[2])) ==
            Orientation::COLLINEAR)
          continue;
        ret.triangles.append(IndexedTriangle{tris(t).v[0], tris(t).v[1], tris(t).v[2]});
      }
 
    // Collect constrained edges.
    ret.constrained_edges.reserve(indexed_constraints.size());
    for (size_t i = 0; i < indexed_constraints.size(); ++i)
      ret.constrained_edges.append(indexed_constraints(i));
 
    return ret;
  }
 
  [[nodiscard]] Result operator () (const std::initializer_list<Point> points,
                                    const std::initializer_list<Segment> constraints) const
  {
    DynList<Point> pts;
    for (const Point &p : points)
      pts.append(p);
 
    DynList<Segment> segs;
    for (const Segment &s : constraints)
      segs.append(s);
 
    return (*this)(pts, segs);
  }
 
  static DynList<Triangle> as_triangles(const Result &result)
  {
    DynList<Triangle> out;
    for (size_t i = 0; i < result.triangles.size(); ++i)
      {
        const auto &[ii, j, k] = result.triangles(i);
        out.append(Triangle(result.sites(ii), result.sites(j), result.sites(k)));
      }
    return out;
  }
};
 
// ============================================================================
// Voronoi Diagram (Dual of Delaunay)
// ============================================================================
 
class VoronoiDiagramFromDelaunay
{
public:
  struct Edge
  {
    size_t site_u;    
    size_t site_v;    
    Point src;        
    Point tgt;        
    bool unbounded;   
    Point direction;  
  };
 
  struct Cell
  {
    size_t site_index;      
    Point site;             
    bool bounded;           
    Array<Point> vertices;  
  };
 
  struct ClippedCell
  {
    size_t site_index;  
    Point site;         
    Polygon polygon;    
  };
 
  struct Result
  {
    Array<Point> sites;     
    Array<Point> vertices;  
    Array<Edge> edges;      
    Array<Cell> cells;      
  };
 
private:
  DelaunayTriangulationBowyerWatson delaunay;  
 
  [[nodiscard]] static Point circumcenter(const Point &a, const Point &b, const Point &c)
  {
    const Geom_Number &ax = a.get_x();
    const Geom_Number &ay = a.get_y();
    const Geom_Number &bx = b.get_x();
    const Geom_Number &by = b.get_y();
    const Geom_Number &cx = c.get_x();
    const Geom_Number &cy = c.get_y();
 
    const Geom_Number a2 = ax * ax + ay * ay;
    const Geom_Number b2 = bx * bx + by * by;
    const Geom_Number c2 = cx * cx + cy * cy;
 
    const Geom_Number d = ax * (by - cy) + bx * (cy - ay) + cx * (ay - by);
    ah_domain_error_if(d == 0) << "Circumcenter undefined for collinear points";
    const Geom_Number den = d + d;
 
    const Geom_Number ux = (a2 * (by - cy) + b2 * (cy - ay) + c2 * (ay - by)) / den;
    const Geom_Number uy = (a2 * (cx - bx) + b2 * (ax - cx) + c2 * (bx - ax)) / den;
 
    return {ux, uy};
  }
 
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &p)
  {
    ah_domain_error_if(not p.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(p.size() < 3) << "Polygon must have at least 3 vertices";
 
    return GeomPolygonUtils::extract_vertices(p);
  }
 
  [[nodiscard]] static bool is_convex(const Array<Point> &verts)
  {
    if (verts.size() < 3)
      return false;
    return GeomPolygonUtils::is_convex(verts);
  }
 
  [[nodiscard]] static HalfPlaneIntersection::HalfPlane bisector_halfplane_for_site(const Point &s,
                                                                                    const Point &t)
  {
    const Point mid((s.get_x() + t.get_x()) / 2, (s.get_y() + t.get_y()) / 2);
 
    const Geom_Number dx = t.get_x() - s.get_x();
    const Geom_Number dy = t.get_y() - s.get_y();
    const Point q(mid.get_x() - dy, mid.get_y() + dx);
 
    return {mid, q};  // the left side contains s
  }
 
  [[nodiscard]] static Array<ClippedCell> indexed_clipped_cells(const Array<Point> &sites,
                                                                const Array<Polygon> &polys)
  {
    ah_domain_error_if(sites.size() != polys.size()) << "Sites and clipped polygons size mismatch";
 
    Array<ClippedCell> ret;
    ret.reserve(sites.size());
 
    for (size_t i = 0; i < sites.size(); ++i)
      {
        ClippedCell cell;
        cell.site_index = i;
        cell.site = sites(i);
        cell.polygon = polys(i);
        ret.append(std::move(cell));
      }
 
    return ret;
  }
 
public:
  [[nodiscard]] Result operator () (const DelaunayTriangulationBowyerWatson::Result &dt) const
  {
    Result ret;
    ret.sites = dt.sites;
 
    if (dt.triangles.is_empty())
      return ret;
 
    Array<Point> centers;
    centers.reserve(dt.triangles.size());
    for (size_t idx = 0; idx < dt.triangles.size(); ++idx)
      {
        const auto &[i, j, k] = dt.triangles(idx);
        centers.append(circumcenter(dt.sites(i), dt.sites(j), dt.sites(k)));
      }
    ret.vertices = centers;
 
    Array<unsigned char> on_hull;
    on_hull.reserve(dt.sites.size());
    for (size_t i = 0; i < dt.sites.size(); ++i)
      on_hull.append(0);
 
    GeomTriangleAdjacencyUtils::for_each_sorted_edge_group(
      dt.triangles,
      [&](const Array<GeomTriangleAdjacencyUtils::EdgeRef> &edges, const size_t first,
          const size_t last)
      {
        if (const size_t cnt = last - first; cnt >= 2)
          {
            const Point &p1 = centers(edges(first).tri);
            const Point &p2 = centers(edges(first + 1).tri);
            ret.edges.append(Edge{edges(first).u, edges(first).v, p1, p2, false, Point()});
            return;
          }
 
        const auto &edge = edges(first);
        const size_t u = edge.u;
        const size_t v = edge.v;
        const size_t tri = edge.tri;
        const size_t third = edge.third;
        on_hull(u) = 1;
        on_hull(v) = 1;
 
        const Point &pu = dt.sites(u);
        const Point &pv = dt.sites(v);
        const Point &pw = dt.sites(third);
 
        const Geom_Number ex = pv.get_x() - pu.get_x();
        const Geom_Number ey = pv.get_y() - pu.get_y();
 
        Geom_Number dirx = -ey;
        Geom_Number diry = ex;
        if (orientation(pu, pv, pw) == Orientation::CCW)
          {
            dirx = ey;
            diry = -ex;
          }
 
        const Point &src = centers(tri);
        ret.edges.append(Edge{u, v, src, src, true, Point(dirx, diry)});
      });
 
    // Pre-build site -> incident triangles index (O(T) instead of O(n*T)).
    Array<Array<size_t>> incidence;
    incidence.reserve(dt.sites.size());
    for (size_t s = 0; s < dt.sites.size(); ++s)
      incidence.append(Array<size_t>());
    for (size_t t = 0; t < dt.triangles.size(); ++t)
      {
        const auto &[ti, tj, tk] = dt.triangles(t);
        incidence(ti).append(t);
        incidence(tj).append(t);
        incidence(tk).append(t);
      }
 
    ret.cells.reserve(dt.sites.size());
    for (size_t s = 0; s < dt.sites.size(); ++s)
      {
        Array<Point> verts;
        verts.reserve(incidence(s).size());
        for (size_t idx = 0; idx < incidence(s).size(); ++idx)
          verts.append(centers(incidence(s)(idx)));
 
        const Point site = dt.sites(s);
        if (verts.size() > 1)
          {
            quicksort_op(verts, [&site](const Point &a, const Point &b)
              {
                const Geom_Number ax = a.get_x() - site.get_x();
                const Geom_Number ay = a.get_y() - site.get_y();
                const Geom_Number bx = b.get_x() - site.get_x();
                const Geom_Number by = b.get_y() - site.get_y();
 
                const bool au = (ay > 0) or (ay == 0 and ax >= 0);
                const bool bu = (by > 0) or (by == 0 and bx >= 0);
                if (au != bu)
                  return au and not bu;
 
                if (const Geom_Number cr = ax * by - ay * bx; cr != 0)
                  return cr > 0;
 
                return (ax * ax + ay * ay) < (bx * bx + by * by);
              });
          }
 
        Array<Point> clean;
        clean.reserve(verts.size());
        for (size_t k = 0; k < verts.size(); ++k)
          if (clean.is_empty() or clean.get_last() != verts(k))
            clean.append(verts(k));
        if (clean.size() > 1 and clean(0) == clean.get_last())
          static_cast<void>(clean.remove_last());
 
        Cell cell;
        cell.site_index = s;
        cell.site = site;
        cell.bounded = on_hull(s) == 0;
        cell.vertices = clean;
        ret.cells.append(std::move(cell));
      }
 
    return ret;
  }
 
  [[nodiscard]] Result operator () (const DynList<Point> &point_set) const
  {
    return (*this)(delaunay(point_set));
  }
 
  [[nodiscard]] Result operator () (const std::initializer_list<Point> il) const
  {
    return (*this)(delaunay(il));
  }
 
  static Array<Polygon> clipped_cells(const Array<Point> &sites, const Polygon &clip)
  {
    const Array<Point> clip_verts = extract_vertices(clip);
    ah_domain_error_if(not is_convex(clip_verts)) << "Clip polygon must be convex";
 
    const Array<HalfPlaneIntersection::HalfPlane> clip_hps =
      HalfPlaneIntersection::from_convex_polygon(clip);
 
    const size_t n = sites.size();
 
    // Compute Delaunay to get adjacency: each site's Voronoi cell is
    // bounded only by bisectors with its Delaunay neighbors (~6 on avg),
    // reducing total complexity from O(n^2 log n) to O(n log n).
    constexpr DelaunayTriangulationBowyerWatson dt_algo;
    DynList<Point> site_list;
    for (size_t i = 0; i < n; ++i)
      site_list.append(sites(i));
    auto dt = dt_algo(site_list);
 
    // Map Delaunay site indices back to input indices.
    // dt.sites may be reordered/deduped, so match by position.
    Array<size_t> dt_to_input;
    dt_to_input.reserve(dt.sites.size());
    for (size_t di = 0; di < dt.sites.size(); ++di)
      {
        size_t match = 0;
        for (size_t oi = 0; oi < n; ++oi)
          if (dt.sites(di) == sites(oi))
            {
              match = oi;
              break;
            }
        dt_to_input.append(match);
      }
 
    // Build adjacency lists from Delaunay triangles (in input-index space)
    Array<DynSetTree<size_t, Treap_Rk>> adj(n);
    for (size_t i = 0; i < n; ++i)
      adj.append(DynSetTree<size_t, Treap_Rk>());
    for (size_t t = 0; t < dt.triangles.size(); ++t)
      {
        const size_t a = dt_to_input(dt.triangles(t).i);
        const size_t b = dt_to_input(dt.triangles(t).j);
        const size_t c = dt_to_input(dt.triangles(t).k);
        adj(a).insert(b);
        adj(a).insert(c);
        adj(b).insert(a);
        adj(b).insert(c);
        adj(c).insert(a);
        adj(c).insert(b);
      }
 
    Array<Polygon> ret;
    ret.reserve(n);
 
    for (size_t i = 0; i < n; ++i)
      {
        HalfPlaneIntersection hpi;
        Array<HalfPlaneIntersection::HalfPlane> hps = clip_hps;
 
        adj(i).for_each([&](size_t j)
          {
            if (sites(j) != sites(i))
              hps.append(bisector_halfplane_for_site(sites(i), sites(j)));
          });
 
        // If a site has no Delaunay neighbors (degenerate case),
        // fall back to the clip polygon alone.
        ret.append(hpi(hps));
      }
 
    return ret;
  }
 
  [[nodiscard]] static Array<Polygon> clipped_cells(const Result &vor, const Polygon &clip)
  {
    return clipped_cells(vor.sites, clip);
  }
 
  [[nodiscard]] Array<Polygon> clipped_cells(const DynList<Point> &point_set, const Polygon &clip) const
  {
    return clipped_cells(delaunay(point_set).sites, clip);
  }
 
  [[nodiscard]] Array<Polygon> clipped_cells(const std::initializer_list<Point> il,
                                             const Polygon &clip) const
  {
    return clipped_cells(delaunay(il).sites, clip);
  }
 
  static Array<ClippedCell> clipped_cells_indexed(const Array<Point> &sites, const Polygon &clip)
  {
    return indexed_clipped_cells(sites, clipped_cells(sites, clip));
  }
 
  [[nodiscard]] static Array<ClippedCell> clipped_cells_indexed(const Result &vor, const Polygon &clip)
  {
    return clipped_cells_indexed(vor.sites, clip);
  }
 
  [[nodiscard]] Array<ClippedCell> clipped_cells_indexed(const DynList<Point> &point_set,
                                                         const Polygon &clip) const
  {
    return clipped_cells_indexed(delaunay(point_set).sites, clip);
  }
 
  [[nodiscard]] Array<ClippedCell> clipped_cells_indexed(const std::initializer_list<Point> il,
                                                         const Polygon &clip) const
  {
    return clipped_cells_indexed(delaunay(il).sites, clip);
  }
};
 
// ============================================================================
// Voronoi Diagram — O(n log n) via Incremental Delaunay Dual
// ============================================================================
 
class VoronoiDiagram
{
  DelaunayTriangulationRandomizedIncremental delaunay_;  
  VoronoiDiagramFromDelaunay voronoi_;                   
 
public:
  using Edge = VoronoiDiagramFromDelaunay::Edge;                
  using Cell = VoronoiDiagramFromDelaunay::Cell;                
  using ClippedCell = VoronoiDiagramFromDelaunay::ClippedCell;  
  using Result = VoronoiDiagramFromDelaunay::Result;            
 
  [[nodiscard]] Result operator () (const DynList<Point> &pts) const
  {
    const auto dt = delaunay_(pts);
    return voronoi_(dt);
  }
 
  [[nodiscard]] Result operator () (const std::initializer_list<Point> il) const
  {
    DynList<Point> pts;
    for (const Point &p : il)
      pts.append(p);
    return (*this)(pts);
  }
 
  [[nodiscard]] Array<ClippedCell> clipped_cells(const DynList<Point> &pts, const Polygon &clip) const
  {
    auto [sites, triangles] = delaunay_(pts);
    return VoronoiDiagramFromDelaunay::clipped_cells_indexed(sites, clip);
  }
};
 
class VoronoiDiagramFortune
{
public:
  using Edge = VoronoiDiagramFromDelaunay::Edge;                
  using Cell = VoronoiDiagramFromDelaunay::Cell;                
  using ClippedCell = VoronoiDiagramFromDelaunay::ClippedCell;  
  using Result = VoronoiDiagramFromDelaunay::Result;            
 
private:
  struct Arc;  
 
  struct Event
  {
    double y = 0.0;        
    double x = 0.0;        
    bool is_site = false;  
    size_t site = 0;       
    Arc *arc = nullptr;    
    size_t id = 0;         
    bool valid = true;     
  };
 
  struct Arc
  {
    size_t site = 0;          
    Arc *prev = nullptr;      
    Arc *next = nullptr;      
    Event *circle = nullptr;  
  };
 
  struct EventCmp
  {
    bool operator () (const Event *a, const Event *b) const
    {
      // DynBinHeap is a min-heap, so define the smallest key as the
      // highest-priority event: max y, then min x, site before circle, then
      // smallest id.
      if (a->y != b->y)
        return a->y > b->y;  // larger y has smaller key
      if (a->x != b->x)
        return a->x < b->x;  // smaller x has smaller key
      if (a->is_site != b->is_site)
        return a->is_site > b->is_site;  // site (0) < circle (1)
      return a->id < b->id;
    }
  };
 
  struct TriKey
  {
    size_t a = 0;
    size_t b = 0;
    size_t c = 0;
 
    bool operator < (const TriKey &o) const
    {
      if (a != o.a)
        return a < o.a;
      if (b != o.b)
        return b < o.b;
      return c < o.c;
    }
  };
 
  static constexpr double kEps = 1e-9;
 
  VoronoiDiagramFromDelaunay voronoi_;
  DelaunayTriangulationBowyerWatson fallback_;
 
  [[nodiscard]] static double as_double(const Geom_Number &v)
  {
    return geom_number_to_double(v);
  }
 
  [[nodiscard]] static bool all_collinear(const Array<Point> &pts)
  {
    if (pts.size() < 3)
      return true;
 
    for (size_t i = 2; i < pts.size(); ++i)
      if (orientation(pts(0), pts(1), pts(i)) != Orientation::COLLINEAR)
        return false;
 
    return true;
  }
 
  [[nodiscard]] static DelaunayTriangulationBowyerWatson::IndexedTriangle
  normalized_triangle(const size_t i, const size_t j, const size_t k, const Array<Point> &sites)
  {
    DelaunayTriangulationBowyerWatson::IndexedTriangle t{i, j, k};
    if (orientation(sites(t.i), sites(t.j), sites(t.k)) == Orientation::CW)
      std::swap(t.j, t.k);
    return t;
  }
 
  [[nodiscard]] static double breakpoint_x(const Point &left_site,
                                           const Point &right_site,
                                           const double sweepline_y)
  {
    const double px = as_double(left_site.get_x());
    const double py = as_double(left_site.get_y());
    const double qx = as_double(right_site.get_x());
    const double qy = as_double(right_site.get_y());
 
    if (std::fabs(py - qy) <= kEps)
      return (px + qx) / 2.0;
    if (std::fabs(py - sweepline_y) <= kEps)
      return px;
    if (std::fabs(qy - sweepline_y) <= kEps)
      return qx;
 
    const double z0 = 2.0 * (py - sweepline_y);
    const double z1 = 2.0 * (qy - sweepline_y);
 
    const double a = 1.0 / z0 - 1.0 / z1;
    const double b = -2.0 * (px / z0 - qx / z1);
    const double c = (px * px + py * py - sweepline_y * sweepline_y) / z0 -
      (qx * qx + qy * qy - sweepline_y * sweepline_y) / z1;
 
    if (std::fabs(a) <= kEps)
      return -c / b;
 
    double disc = b * b - 4.0 * a * c;
    if (disc < 0.0 and disc > -kEps)
      disc = 0.0;
    ah_domain_error_if(disc < 0.0) << "Negative discriminant in Fortune breakpoint";
 
    const double sq = std::sqrt(disc);
    const double x1 = (-b - sq) / (2.0 * a);
    const double x2 = (-b + sq) / (2.0 * a);
    return py < qy ? std::max(x1, x2) : std::min(x1, x2);
  }
 
  [[nodiscard]] static Arc *locate_arc(Arc *head,
                                       const Array<Point> &sites,
                                       const double x,
                                       const double sweepline_y)
  {
    if (head == nullptr)
      return nullptr;
 
    for (Arc *arc = head; arc != nullptr; arc = arc->next)
      {
        const double left = arc->prev == nullptr
          ? -std::numeric_limits<double>::infinity()
          : breakpoint_x(sites(arc->prev->site), sites(arc->site), sweepline_y);
        const double right = arc->next == nullptr
          ? std::numeric_limits<double>::infinity()
          : breakpoint_x(sites(arc->site), sites(arc->next->site), sweepline_y);
 
        if (x >= left - kEps and x <= right + kEps)
          return arc;
      }
 
    Arc *tail = head;
    while (tail->next != nullptr)
      tail = tail->next;
    return tail;
  }
 
  static void invalidate_circle_event(Arc *arc)
  {
    if (arc != nullptr and arc->circle != nullptr)
      {
        arc->circle->valid = false;
        arc->circle = nullptr;
      }
  }
 
  static void enqueue_circle_event(Arc *arc,
                                   const double sweepline_y,
                                   const Array<Point> &sites,
                                   DynBinHeap<Event *, EventCmp> &queue,
                                   Array<std::unique_ptr<Event>> &event_pool,
                                   size_t &next_event_id)
  {
    invalidate_circle_event(arc);
 
    if (arc == nullptr or arc->prev == nullptr or arc->next == nullptr)
      return;
 
    const size_t ia = arc->prev->site;
    const size_t ib = arc->site;
    const size_t ic = arc->next->site;
    if (ia == ib or ib == ic or ia == ic)
      return;
 
    const Point &a = sites(ia);
    const Point &b = sites(ib);
    const Point &c = sites(ic);
 
    if (orientation(a, b, c) != Orientation::CW)
      return;
 
    const double ax = as_double(a.get_x());
    const double ay = as_double(a.get_y());
    const double bx = as_double(b.get_x());
    const double by = as_double(b.get_y());
    const double cx = as_double(c.get_x());
    const double cy = as_double(c.get_y());
 
    const double det = 2.0 * (ax * (by - cy) + bx * (cy - ay) + cx * (ay - by));
    if (std::fabs(det) <= kEps)
      return;
 
    const double a2 = ax * ax + ay * ay;
    const double b2 = bx * bx + by * by;
    const double c2 = cx * cx + cy * cy;
 
    const double ux = (a2 * (by - cy) + b2 * (cy - ay) + c2 * (ay - by)) / det;
    const double uy = (a2 * (cx - bx) + b2 * (ax - cx) + c2 * (bx - ax)) / det;
 
    const double r = std::hypot(ax - ux, ay - uy);
    const double event_y = uy - r;
    if (event_y >= sweepline_y - kEps)
      return;
 
    event_pool.append(std::make_unique<Event>());
    Event *ev = event_pool.get_last().get();
    ev->y = event_y;
    ev->x = ux;
    ev->is_site = false;
    ev->site = 0;
    ev->arc = arc;
    ev->id = next_event_id++;
    ev->valid = true;
 
    arc->circle = ev;
    queue.put(ev);
  }
 
  [[nodiscard]] static bool is_valid_delaunay(const DelaunayTriangulationBowyerWatson::Result &dt)
  {
    for (size_t t = 0; t < dt.triangles.size(); ++t)
      {
        const auto &[i, j, k] = dt.triangles(t);
        const Point &a = dt.sites(i);
        const Point &b = dt.sites(j);
        const Point &c = dt.sites(k);
        const Orientation o = orientation(a, b, c);
        if (o == Orientation::COLLINEAR)
          return false;
 
        for (size_t p = 0; p < dt.sites.size(); ++p)
          {
            if (p == i or p == j or p == k)
              continue;
 
            if (const Geom_Number det = in_circle_determinant(a, b, c, dt.sites(p));
                (o == Orientation::CCW and det > 0) or (o == Orientation::CW and det < 0))
              return false;
          }
      }
 
    return true;
  }
 
  static DelaunayTriangulationBowyerWatson::Result triangulate_sweep(const Array<Point> &sites)
  {
    using DTResult = DelaunayTriangulationBowyerWatson::Result;
    using DTTriangle = DelaunayTriangulationBowyerWatson::IndexedTriangle;
 
    DTResult out;
    out.sites = sites;
 
    const size_t n = sites.size();
    if (n < 3 or all_collinear(sites))
      return out;
 
    DynBinHeap<Event *, EventCmp> queue;
    auto event_pool = Array<std::unique_ptr<Event>>::create(4 * n + 8);
    auto arc_pool = Array<std::unique_ptr<Arc>>::create(3 * n + 8);
 
    auto make_arc = [&](const size_t site_idx) -> Arc *
      {
        arc_pool.append(std::make_unique<Arc>());
        Arc *a = arc_pool.get_last().get();
        a->site = site_idx;
        return a;
      };
 
    size_t next_event_id = 1;
    for (size_t i = 0; i < n; ++i)
      {
        event_pool.append(std::make_unique<Event>());
        Event *ev = event_pool.get_last().get();
        ev->y = as_double(sites(i).get_y());
        ev->x = as_double(sites(i).get_x());
        ev->is_site = true;
        ev->site = i;
        ev->id = next_event_id++;
        queue.put(ev);
      }
 
    Arc *head = nullptr;
 
    DynSetTree<TriKey> seen;
    Array<DTTriangle> tris;
    tris.reserve(2 * n);
 
    auto append_triangle = [&](const size_t i, const size_t j, const size_t k)
      {
        if (i == j or j == k or i == k)
          return;
        if (orientation(sites(i), sites(j), sites(k)) == Orientation::COLLINEAR)
          return;
 
        size_t a = i, b = j, c = k;
        if (a > b)
          std::swap(a, b);
        if (b > c)
          std::swap(b, c);
        if (a > b)
          std::swap(a, b);
 
        if (const auto ptr = seen.insert(TriKey{a, b, c}); ptr == nullptr)
          return;
 
        tris.append(normalized_triangle(i, j, k, sites));
      };
 
    while (not queue.is_empty())
      {
        const Event *ev = queue.get();
        if (not ev->valid)
          continue;
 
        const double ly = ev->y;
 
        if (ev->is_site)
          {
            const size_t site_idx = ev->site;
            const double sx = as_double(sites(site_idx).get_x());
 
            if (head == nullptr)
              {
                head = make_arc(site_idx);
                continue;
              }
 
            Arc *arc = locate_arc(head, sites, sx, ly - 10.0 * kEps);
            ah_domain_error_if(arc == nullptr) << "Could not locate arc in Fortune site event";
 
            invalidate_circle_event(arc);
 
            Arc *middle = make_arc(site_idx);
            Arc *right = make_arc(arc->site);
 
            right->next = arc->next;
            if (right->next != nullptr)
              right->next->prev = right;
 
            arc->next = middle;
            middle->prev = arc;
            middle->next = right;
            right->prev = middle;
 
            enqueue_circle_event(arc, ly, sites, queue, event_pool, next_event_id);
            enqueue_circle_event(right, ly, sites, queue, event_pool, next_event_id);
          }
        else
          {
            Arc *arc = ev->arc;
            if (arc == nullptr or arc->circle != ev)
              continue;
 
            Arc *left = arc->prev;
            Arc *right = arc->next;
            if (left == nullptr or right == nullptr)
              continue;
 
            append_triangle(left->site, arc->site, right->site);
 
            invalidate_circle_event(left);
            invalidate_circle_event(arc);
            invalidate_circle_event(right);
 
            left->next = right;
            right->prev = left;
 
            enqueue_circle_event(left, ly, sites, queue, event_pool, next_event_id);
            enqueue_circle_event(right, ly, sites, queue, event_pool, next_event_id);
          }
      }
 
    out.triangles = std::move(tris);
    return out;
  }
 
public:
  [[nodiscard]] Result operator () (const DynList<Point> &pts) const
  {
    // Reuse canonical site handling and keep a robust fallback path.
    const auto dt_ref = fallback_(pts);
    if (dt_ref.sites.size() < 3 or dt_ref.triangles.is_empty())
      return voronoi_(dt_ref);
 
    const auto dt_sweep = triangulate_sweep(dt_ref.sites);
    if (dt_sweep.triangles.is_empty() or dt_sweep.triangles.size() != dt_ref.triangles.size() or
        not is_valid_delaunay(dt_sweep))
      return voronoi_(dt_ref);
 
    return voronoi_(dt_sweep);
  }
 
  [[nodiscard]] Result operator () (const std::initializer_list<Point> il) const
  {
    DynList<Point> pts;
    for (const Point &p : il)
      pts.append(p);
    return (*this)(pts);
  }
 
  [[nodiscard]] Array<ClippedCell> clipped_cells(const DynList<Point> &pts, const Polygon &clip) const
  {
    return VoronoiDiagramFromDelaunay::clipped_cells_indexed((*this)(pts), clip);
  }
 
  [[nodiscard]] Array<ClippedCell> clipped_cells(const std::initializer_list<Point> il,
                                                 const Polygon &clip) const
  {
    DynList<Point> pts;
    for (const Point &p : il)
      pts.append(p);
    return clipped_cells(pts, clip);
  }
};
 
// ============================================================================
// Convex Hull Algorithms
// ============================================================================
 
class AndrewMonotonicChainConvexHull
{
  struct LexicographicCmp
  {
    bool operator () (const Point &p1, const Point &p2) const
    {
      if (p1.get_x() < p2.get_x())
        return true;
 
      if (p2.get_x() < p1.get_x())
        return false;
 
      return p1.get_y() < p2.get_y();
    }
  };
 
  static Array<Point> sorted_unique_points(const DynList<Point> &point_set)
  {
    Array<Point> points;
    for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
      points.append(it.get_curr());
 
    if (points.size() <= 1)
      return points;
 
    quicksort_op(points, LexicographicCmp());
 
    Array<Point> unique;
    unique.reserve(points.size());
    unique.append(points(0));
    for (size_t i = 1; i < points.size(); ++i)
      if (points(i) != unique.get_last())
        unique.append(points(i));
 
    return unique;
  }
 
  [[nodiscard]] static Geom_Number turn(const Point &a, const Point &b, const Point &c)
  {
    return area_of_parallelogram(a, b, c);
  }
 
public:
  Polygon operator () (const DynList<Point> &point_set) const
  {
    Polygon ret;
    Array<Point> points = sorted_unique_points(point_set);
    const size_t n = points.size();
 
    if (n == 0)
      return ret;
 
    if (n == 1)
      {
        ret.add_vertex(points(0));
        return ret;
      }
 
    Array<Point> lower;
    lower.reserve(n);
    for (size_t i = 0; i < n; ++i)
      {
        while (lower.size() >= 2 &&
               turn(lower(lower.size() - 2), lower(lower.size() - 1), points(i)) <= 0)
          static_cast<void>(lower.remove_last());
        lower.append(points(i));
      }
 
    Array<Point> upper;
    upper.reserve(n);
    for (size_t i = n; i > 0; --i)
      {
        const Point &p = points(i - 1);
        while (upper.size() >= 2 && turn(upper(upper.size() - 2), upper(upper.size() - 1), p) <= 0)
          static_cast<void>(upper.remove_last());
        upper.append(p);
      }
 
    // Remove duplicate endpoints before concatenating chains.
    static_cast<void>(lower.remove_last());
    static_cast<void>(upper.remove_last());
 
    for (size_t i = 0; i < lower.size(); ++i)
      ret.add_vertex(lower(i));
 
    for (size_t i = 0; i < upper.size(); ++i)
      ret.add_vertex(upper(i));
 
    if (ret.size() >= 3)
      ret.close();
 
    return ret;
  }
};
 
class GrahamScanConvexHull
{
  struct LexicographicCmp
  {
    bool operator () (const Point &p1, const Point &p2) const
    {
      if (p1.get_x() < p2.get_x())
        return true;
 
      if (p2.get_x() < p1.get_x())
        return false;
 
      return p1.get_y() < p2.get_y();
    }
  };
 
  static Array<Point> sorted_unique_points(const DynList<Point> &point_set)
  {
    Array<Point> points;
    for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
      points.append(it.get_curr());
 
    if (points.size() <= 1)
      return points;
 
    quicksort_op(points, LexicographicCmp());
 
    Array<Point> unique;
    unique.reserve(points.size());
    unique.append(points(0));
    for (size_t i = 1; i < points.size(); ++i)
      if (points(i) != unique.get_last())
        unique.append(points(i));
 
    return unique;
  }
 
  [[nodiscard]] static Geom_Number turn(const Point &a, const Point &b, const Point &c)
  {
    return area_of_parallelogram(a, b, c);
  }
 
public:
  Polygon operator () (const DynList<Point> &point_set) const
  {
    Polygon ret;
    Array<Point> points = sorted_unique_points(point_set);
    const size_t n = points.size();
 
    if (n == 0)
      return ret;
 
    if (n == 1)
      {
        ret.add_vertex(points(0));
        return ret;
      }
 
    // Pivot = lowest y, and lowest x on ties.
    size_t pivot_idx = 0;
    for (size_t i = 1; i < n; ++i)
      {
        if (points(i).get_y() < points(pivot_idx).get_y())
          {
            pivot_idx = i;
            continue;
          }
 
        if (points(i).get_y() == points(pivot_idx).get_y() &&
            points(i).get_x() < points(pivot_idx).get_x())
          pivot_idx = i;
      }
 
    const Point pivot = points(pivot_idx);
    if (pivot_idx != 0)
      {
        const Point tmp = points(0);
        points(0) = points(pivot_idx);
        points(pivot_idx) = tmp;
      }
 
    Array<Point> polar;
    polar.reserve(n - 1);
    for (size_t i = 1; i < n; ++i)
      polar.append(points(i));
 
    quicksort_op(polar, [&pivot](const Point &a, const Point &b)
      {
        const Geom_Number area = area_of_parallelogram(pivot, a, b);
        if (area > 0)
          return true;
        if (area < 0)
          return false;
 
        // Same angle: keep nearer first; later we keep only farthest.
        return pivot.distance_squared_to(a) < pivot.distance_squared_to(b);
      });
 
    // Keep only the farthest point per polar direction.
    Array<Point> filtered;
    filtered.reserve(polar.size());
    for (size_t i = 0; i < polar.size();)
      {
        size_t j = i;
        while (j + 1 < polar.size() && area_of_parallelogram(pivot, polar(j), polar(j + 1)) == 0)
          ++j;
        filtered.append(polar(j));
        i = j + 1;
      }
 
    if (filtered.size() == 1)
      {
        ret.add_vertex(pivot);
        ret.add_vertex(filtered(0));
        // Cannot close with only 2 vertices - return unclosed degenerate hull
        return ret;
      }
 
    Array<Point> hull;
    hull.reserve(filtered.size() + 1);
    hull.append(pivot);
    hull.append(filtered(0));
 
    for (size_t i = 1; i < filtered.size(); ++i)
      {
        const Point &p = filtered(i);
        while (hull.size() >= 2 && turn(hull(hull.size() - 2), hull(hull.size() - 1), p) <= 0)
          static_cast<void>(hull.remove_last());
        hull.append(p);
      }
 
    for (size_t i = 0; i < hull.size(); ++i)
      ret.add_vertex(hull(i));
 
    if (ret.size() >= 3)
      ret.close();
 
    return ret;
  }
};
 
class BruteForceConvexHull
{
  struct CmpSegment
  {
    static bool cmp_point(const Point &p1, const Point &p2)
    {
      if (p1.get_x() < p2.get_x())
        return true;
 
      return not (p2.get_x() < p1.get_x()) and p1.get_y() < p2.get_y();
    }
 
    bool operator () (const Segment &s1, const Segment &s2) const
    {
      if (cmp_point(s1.get_src_point(), s2.get_src_point()))
        return true;
 
      return not (cmp_point(s2.get_src_point(), s1.get_src_point())) and
        cmp_point(s1.get_tgt_point(), s2.get_tgt_point());
    }
  };
 
  using SegmentSet = DynSetTree<Segment, Treap_Rk, CmpSegment>;
  using PointIt = DynList<Point>::Iterator;
 
  static bool are_all_points_on_left(const DynList<Point> &l, const Segment &s)
  {
    for (PointIt it(l); it.has_curr(); it.next_ne())
      if (const Point &p = it.get_curr(); p.is_right_of(s))
        return false;
 
    return true;
  }
 
  static SegmentSet extreme_edges(const DynList<Point> &point_set)
  {
    SegmentSet ret;
 
    for (PointIt i(point_set); i.has_curr(); i.next_ne())
      {
        const Point &p_i = i.get_curr();
 
        for (PointIt j(point_set); j.has_curr(); j.next_ne())
          {
            const Point &p_j = j.get_curr();
 
            if (p_i == p_j)
              continue;
 
            if (Segment s(p_i, p_j); are_all_points_on_left(point_set, s))
              ret.insert(s);
          }
      }
 
    return ret;
  }
 
public:
  Polygon operator () (const DynList<Point> &point_set) const
  {
    Polygon ret;
 
    if (point_set.is_empty())
      return ret;
 
    PointIt check_it(point_set);
    const Point first = check_it.get_curr();
    bool has_distinct = false;
    check_it.next();
    for (; check_it.has_curr(); check_it.next_ne())
      if (check_it.get_curr() != first)
        {
          has_distinct = true;
          break;
        }
 
    if (not has_distinct)
      {
        ret.add_vertex(first);
        return ret;
      }
 
    SegmentSet extremes = extreme_edges(point_set);
 
    const Segment first_segment = extremes.remove_pos(0);
    ret.add_vertex(first_segment.get_src_point());
    ret.add_vertex(first_segment.get_tgt_point());
 
    while (true)
      {
        const Vertex &last_vertex = ret.get_last_vertex();
 
        const Segment *ptr = extremes.find_ptr([&last_vertex](const Segment &s)
          {
            return s.get_src_point() == last_vertex;
          });
 
        ah_domain_error_if(ptr == nullptr)
          << "BruteForceConvexHull: broken chain (degenerate input?)";
 
        if (ptr->get_tgt_point() == ret.get_first_vertex())
          break;
 
        ret.add_vertex(ptr->get_tgt_point());
 
        extremes.remove(*ptr);
      }
 
    if (ret.size() >= 3)
      ret.close();
    return ret;
  }
};
 
class GiftWrappingConvexHull
{
  static const Point *get_lowest_point(const DynList<Point> &point_set)
  {
    DynList<Point>::Iterator it(point_set);
    const Point *ret = &it.get_curr();
    it.next();
 
    for (/* nothing */; it.has_curr(); it.next_ne())
      {
        const Point &p = it.get_curr();
        if (p.get_y() < ret->get_y() or (p.get_y() == ret->get_y() and p.get_x() < ret->get_x()))
          ret = &p;
      }
 
    return ret;
  }
 
public:
  Polygon operator () (const DynList<Point> &point_set) const
  {
    Polygon ret;
 
    if (point_set.is_empty())
      return ret;
 
    const Point *start = get_lowest_point(point_set);
    const Point *current = start;
 
    do
      {
        ret.add_vertex(*current);
        const Point *next = nullptr;
 
        for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
          {
            const Point &candidate = it.get_curr();
 
            if (candidate == *current)
              continue;
 
            if (next == nullptr)
              {
                next = &candidate;
                continue;
              }
 
            if (const Orientation o = orientation(*current, *next, candidate); o == Orientation::CW)
              next = &candidate;
            else if (o == Orientation::COLLINEAR and
                     current->distance_squared_to(candidate) > current->distance_squared_to(*next))
              next = &candidate;
          }
 
        if (next == nullptr)
          break;
 
        current = next;
    } while (current != start);
 
    if (ret.size() >= 3)
      ret.close();
    return ret;
  }
};
 
class QuickHull
{
  static Point get_farthest_point(const DynList<Point> &point_set, const Segment &s)
  {
    // Compare perpendicular distances via |area_of_parallelogram|.
    // Since the segment base is constant for all candidates, comparing
    // |area| is equivalent to comparing distance (avoids sqrt).
    Geom_Number max_area = 0;
    Point ret;
    const Point &a = s.get_src_point();
    const Point &b = s.get_tgt_point();
 
    for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
      {
        const Point &p = it.get_curr();
        Geom_Number area = area_of_parallelogram(a, b, p);
        if (area < 0)
          area = -area;
 
        if (area > max_area)
          {
            ret = p;
            max_area = area;
          }
      }
 
    return ret;
  }
 
  static std::pair<DynList<Point>, DynList<Point>> get_right_points(DynList<Point> &point_set,
                                                                    const Point &a,
                                                                    const Point &b,
                                                                    const Point &c)
  {
    std::pair<DynList<Point>, DynList<Point>> ret;
 
    while (not point_set.is_empty())
      {
        Point p = point_set.remove_first();
 
        if (p != a and p != c and area_of_parallelogram(a, c, p) < 0)
          {
            ret.first.append(p);
            continue;
          }
 
        if (p != c and p != b and area_of_parallelogram(c, b, p) < 0)
          ret.second.append(p);
      }
 
    return ret;
  }
 
  static DynList<Point> quick_hull(DynList<Point> &point_set, const Point &a, const Point &b)
  {
    if (point_set.is_empty())
      return {};
 
    const Point c = get_farthest_point(point_set, Segment(a, b));
 
    auto [s_ac, s_bc] = get_right_points(point_set, a, b, c);
 
    DynList<Point> ret = quick_hull(s_ac, a, c);
    DynList<Point> tmp = quick_hull(s_bc, c, b);
    ret.append(c);
    ret.concat(tmp);
 
    return ret;
  }
 
  static std::pair<Point, Point> search_extremes(const DynList<Point> &point_set)
  {
    DynList<Point>::Iterator it(point_set);
    Point leftmost = it.get_curr();
    Point rightmost = it.get_curr();
    it.next();
 
    for (/* nothing */; it.has_curr(); it.next_ne())
      {
        const Point &p = it.get_curr();
 
        if (p.get_x() < leftmost.get_x())
          leftmost = p;
 
        if (p.get_x() > rightmost.get_x())
          rightmost = p;
      }
 
    return std::make_pair(leftmost, rightmost);
  }
 
  static std::pair<DynList<Point>, DynList<Point>> partition(const DynList<Point> &point_set,
                                                             const Point &a,
                                                             const Point &b)
  {
    std::pair<DynList<Point>, DynList<Point>> ret;
 
    for (DynList<Point>::Iterator it(point_set); it.has_curr(); it.next_ne())
      if (const Point &p = it.get_curr(); area_of_parallelogram(a, b, p) < 0)
        ret.first.append(p);
      else
        ret.second.append(p);
 
    return ret;
  }
 
public:
  Polygon operator () (const DynList<Point> &point_set) const
  {
    Polygon ret;
 
    if (point_set.is_empty())
      return ret;
 
    const auto [leftmost, rightmost] = search_extremes(point_set);
    if (leftmost == rightmost)
      {
        ret.add_vertex(leftmost);
        return ret;
      }
 
    auto [right, left_or_collinear] = partition(point_set, leftmost, rightmost);
 
    DynList<Point> s1 = quick_hull(right, leftmost, rightmost);
    DynList<Point> s2 = quick_hull(left_or_collinear, rightmost, leftmost);
 
    DynList<Point> convex_set;
    convex_set.append(leftmost);
    convex_set.concat(s1);
    convex_set.append(rightmost);
    convex_set.concat(s2);
 
    for (DynList<Point>::Iterator it(convex_set); it.has_curr(); it.next_ne())
      ret.add_vertex(it.get_curr());
 
    if (ret.size() >= 3)
      ret.close();
    return ret;
  }
};
 
// ============================================================================
// Segment-Segment Intersection (Dedicated O(1))
// ============================================================================
 
class SegmentSegmentIntersection
{
public:
  enum class Kind
  {
    NONE,    
    POINT,   
    OVERLAP  
  };
 
  struct Result
  {
    Kind kind = Kind::NONE;     
    Point point = Point(0, 0);  
    Segment overlap =
      Segment(Point(0, 0), Point(0, 0));  
 
    [[nodiscard]] bool intersects() const noexcept
    {
      return kind != Kind::NONE;
    }
  };
 
private:
  [[nodiscard]] static bool point_less_on_axis(const Point &a, const Point &b, const bool vertical_axis)
  {
    if (vertical_axis)
      {
        if (a.get_y() != b.get_y())
          return a.get_y() < b.get_y();
        return a.get_x() < b.get_x();
      }
 
    if (a.get_x() != b.get_x())
      return a.get_x() < b.get_x();
    return a.get_y() < b.get_y();
  }
 
  [[nodiscard]] static Point point_max_on_axis(const Point &a, const Point &b, const bool vertical_axis)
  {
    return point_less_on_axis(a, b, vertical_axis) ? b : a;
  }
 
  [[nodiscard]] static Point point_min_on_axis(const Point &a, const Point &b, const bool vertical_axis)
  {
    return point_less_on_axis(a, b, vertical_axis) ? a : b;
  }
 
  [[nodiscard]] static Segment collinear_overlap(const Segment &s1, const Segment &s2)
  {
    const bool vertical_axis = s1.get_src_point().get_x() == s1.get_tgt_point().get_x();
 
    Point a0 = s1.get_src_point();
    Point a1 = s1.get_tgt_point();
    Point b0 = s2.get_src_point();
    Point b1 = s2.get_tgt_point();
 
    if (point_less_on_axis(a1, a0, vertical_axis))
      std::swap(a0, a1);
    if (point_less_on_axis(b1, b0, vertical_axis))
      std::swap(b0, b1);
 
    const Point lo = point_max_on_axis(a0, b0, vertical_axis);
    const Point hi = point_min_on_axis(a1, b1, vertical_axis);
    return Segment(lo, hi);
  }
 
public:
  [[nodiscard]] Result operator () (const Segment &s1, const Segment &s2) const
  {
    Result out;
 
    if (not segments_intersect(s1, s2))
      return out;
 
    if (not s1.is_parallel_with(s2))
      {
        out.kind = Kind::POINT;
        out.point = s1.intersection_with(s2);
        return out;
      }
 
    out.overlap = collinear_overlap(s1, s2);
    if (out.overlap.get_src_point() == out.overlap.get_tgt_point())
      {
        out.kind = Kind::POINT;
        out.point = out.overlap.get_src_point();
        return out;
      }
 
    out.kind = Kind::OVERLAP;
    return out;
  }
};
 
[[nodiscard]] inline SegmentSegmentIntersection::Result segment_segment_intersection(const Segment &s1,
                                                                                     const Segment &s2)
{
  return SegmentSegmentIntersection{}(s1, s2);
}
 
// ============================================================================
// Line Sweep / Event-Driven Framework
// ============================================================================
 
template <typename Event, typename CmpEvent>
class LineSweepFramework
{
  struct SeqEvent
  {
    Event event;  
    size_t seq;   
  };
 
  struct CmpSeqEvent
  {
    CmpEvent cmp;  
 
    bool operator () (const SeqEvent &a, const SeqEvent &b) const
    {
      if (cmp(a.event, b.event))
        return true;
      if (cmp(b.event, a.event))
        return false;
      return a.seq < b.seq;
    }
  };
 
  DynSetTree<SeqEvent, Avl_Tree, CmpSeqEvent> queue_;
  size_t seq_ = 0;
 
public:
  void enqueue(const Event &e)
  {
    queue_.insert(SeqEvent{e, seq_++});
  }
 
  void enqueue(Event &&e)
  {
    queue_.insert(SeqEvent{std::move(e), seq_++});
  }
 
  [[nodiscard]] bool has_events() const noexcept
  {
    return not queue_.is_empty();
  }
 
  [[nodiscard]] size_t pending() const noexcept
  {
    return queue_.size();
  }
 
  Event dequeue()
  {
    SeqEvent se = queue_.min();
    queue_.remove(se);
    return std::move(se.event);
  }
 
  [[nodiscard]] const Event &peek() const
  {
    return queue_.min().event;
  }
 
  void clear() noexcept
  {
    queue_.empty();  // DynSetTree::empty() is a mutator that removes all elements
    seq_ = 0;
  }
 
  template <typename Handler>
  void run(Handler &&handler)
  {
    while (has_events())
      handler(*this, dequeue());
  }
 
  template <typename Handler>
  void run(Handler &&handler, Array<Event> &out)
  {
    while (has_events())
      {
        Event e = dequeue();
        out.append(e);
        handler(*this, e);
      }
  }
};
 
// ============================================================================
// Sweep Line Segment Intersection (Bentley-Ottmann)
// ============================================================================
 
class SweepLineSegmentIntersection
{
public:
  struct Intersection
  {
    size_t seg_i;  
    size_t seg_j;  
    Point point;   
  };
 
private:
  [[nodiscard]] static Geom_Number y_at_x(const Segment &s, const Geom_Number &x)
  {
    const Geom_Number &x1 = s.get_src_point().get_x();
    const Geom_Number &y1 = s.get_src_point().get_y();
    const Geom_Number &x2 = s.get_tgt_point().get_x();
    const Geom_Number &y2 = s.get_tgt_point().get_y();
 
    if (x1 == x2)
      return (y1 + y2) / 2;
 
    return y1 + (x - x1) * (y2 - y1) / (x2 - x1);
  }
 
  [[nodiscard]] static Segment canonicalize(const Segment &s)
  {
    const Point &a = s.get_src_point();
    const Point &b = s.get_tgt_point();
 
    if (a.get_x() < b.get_x())
      return s;
    if (b.get_x() < a.get_x())
      return {b, a};
    // Vertical: lower endpoint first.
    if (a.get_y() < b.get_y())
      return s;
    return {b, a};
  }
 
  enum class EventType
  {
    LEFT,
    INTERSECTION,
    RIGHT
  };
 
  struct Event
  {
    Point pt;        
    EventType type;  
    size_t seg_a;    
    size_t seg_b;    
  };
 
  [[nodiscard]] static bool event_less(const Event &a, const Event &b)
  {
    if (a.pt.get_x() != b.pt.get_x())
      return a.pt.get_x() < b.pt.get_x();
    if (a.pt.get_y() != b.pt.get_y())
      return a.pt.get_y() < b.pt.get_y();
    // LEFT < INTERSECTION < RIGHT for the same point.
    return static_cast<int>(a.type) < static_cast<int>(b.type);
  }
 
  struct EventLess
  {
    bool operator () (const Event &a, const Event &b) const
    {
      return event_less(a, b);
    }
  };
 
  [[nodiscard]] static bool slope_less(const Segment &a, const Segment &b)
  {
    const Geom_Number adx = a.get_tgt_point().get_x() - a.get_src_point().get_x();
    const Geom_Number ady = a.get_tgt_point().get_y() - a.get_src_point().get_y();
    const Geom_Number bdx = b.get_tgt_point().get_x() - b.get_src_point().get_x();
    const Geom_Number bdy = b.get_tgt_point().get_y() - b.get_src_point().get_y();
 
    if (adx == 0 and bdx == 0)
      return ady < bdy;
    if (adx == 0)
      return false;  // +inf slope
    if (bdx == 0)
      return true;
 
    const Geom_Number lhs = ady * bdx;
    const Geom_Number rhs = bdy * adx;
    return lhs < rhs;
  }
 
  [[nodiscard]] static bool status_less(const size_t lhs,
                                        const size_t rhs,
                                        const Geom_Number &sx,
                                        const Array<Segment> &segs)
  {
    if (lhs == rhs)
      return false;
 
    const Geom_Number yl = y_at_x(segs(lhs), sx);
    const Geom_Number yr = y_at_x(segs(rhs), sx);
    if (yl != yr)
      return yl < yr;
 
    if (slope_less(segs(lhs), segs(rhs)))
      return true;
    if (slope_less(segs(rhs), segs(lhs)))
      return false;
 
    return lhs < rhs;
  }
 
  class StatusTree
  {
    struct Node
    {
      size_t seg;
      Geom_Number label;
      unsigned priority;
      Node *left = nullptr;
      Node *right = nullptr;
    };
 
    Node *root_ = nullptr;
    const Array<Segment> &segs_;
    std::mt19937 rng_{0x5f3759dfu};
    Array<Node *> nodes_;
 
    [[nodiscard]] static Node *merge(Node *a, Node *b)
    {
      if (a == nullptr)
        return b;
      if (b == nullptr)
        return a;
      if (a->priority < b->priority)
        {
          a->right = merge(a->right, b);
          return a;
        }
      b->left = merge(a, b->left);
      return b;
    }
 
    [[nodiscard]] static Node *insert_by_label(Node *root, Node *node)
    {
      if (root == nullptr)
        return node;
 
      if (node->priority < root->priority)
        {
          Node *left = nullptr;
          Node *right = nullptr;
          split_by_label(root, node->label, left, right);
          node->left = left;
          node->right = right;
          return node;
        }
 
      if (node->label < root->label)
        root->left = insert_by_label(root->left, node);
      else
        root->right = insert_by_label(root->right, node);
      return root;
    }
 
    static void split_by_label(Node *root, const Geom_Number &label, Node *&left, Node *&right)
    {
      if (root == nullptr)
        {
          left = nullptr;
          right = nullptr;
          return;
        }
 
      if (root->label < label)
        {
          split_by_label(root->right, label, root->right, right);
          left = root;
        }
      else
        {
          split_by_label(root->left, label, left, root->left);
          right = root;
        }
    }
 
    [[nodiscard]] static Node *erase_by_label(Node *root, const Geom_Number &label, Node *&removed)
    {
      if (root == nullptr)
        return nullptr;
 
      if (label < root->label)
        {
          root->left = erase_by_label(root->left, label, removed);
          return root;
        }
 
      if (root->label < label)
        {
          root->right = erase_by_label(root->right, label, removed);
          return root;
        }
 
      removed = root;
      return merge(root->left, root->right);
    }
 
    static void destroy(const Node *n)
    {
      if (n == nullptr)
        return;
      destroy(n->left);
      destroy(n->right);
      delete n;
    }
 
    [[nodiscard]] size_t predecessor_for_insert(const size_t seg, const Geom_Number &sx) const
    {
      size_t pred = SIZE_MAX;
      const Node *cur = root_;
      while (cur != nullptr)
        if (status_less(cur->seg, seg, sx, segs_))
          {
            pred = cur->seg;
            cur = cur->right;
          }
        else
          cur = cur->left;
      return pred;
    }
 
    [[nodiscard]] size_t successor_for_insert(const size_t seg, const Geom_Number &sx) const
    {
      size_t succ = SIZE_MAX;
      const Node *cur = root_;
      while (cur != nullptr)
        if (status_less(seg, cur->seg, sx, segs_))
          {
            succ = cur->seg;
            cur = cur->left;
          }
        else
          cur = cur->right;
      return succ;
    }
 
    [[nodiscard]] Geom_Number fresh_label_between(const size_t pred, const size_t succ) const
    {
      if (pred != SIZE_MAX and succ != SIZE_MAX)
        return (nodes_(pred)->label + nodes_(succ)->label) / Geom_Number(2);
      if (pred != SIZE_MAX)
        return nodes_(pred)->label + Geom_Number(1);
      if (succ != SIZE_MAX)
        return nodes_(succ)->label - Geom_Number(1);
      return Geom_Number(0);
    }
 
  public:
    explicit StatusTree(const Array<Segment> &segs) : segs_(segs)
    {
      nodes_.reserve(segs.size());
      for (size_t i = 0; i < segs.size(); ++i)
        nodes_.append(nullptr);
    }
 
    ~StatusTree()
    {
      destroy(root_);
    }
 
    [[nodiscard]] bool contains(const size_t seg) const
    {
      return nodes_(seg) != nullptr;
    }
 
    void insert(const size_t seg, const Geom_Number &sx)
    {
      if (contains(seg))
        return;
 
      const size_t pred = predecessor_for_insert(seg, sx);
      const size_t succ = successor_for_insert(seg, sx);
      const auto node = new Node{seg, fresh_label_between(pred, succ),
                                 static_cast<unsigned>(rng_()), nullptr, nullptr};
      root_ = insert_by_label(root_, node);
      nodes_(seg) = node;
    }
 
    void erase(const size_t seg)
    {
      if (not contains(seg))
        return;
 
      Node *removed = nullptr;
      root_ = erase_by_label(root_, nodes_(seg)->label, removed);
      nodes_(seg) = nullptr;
      delete removed;
    }
 
    [[nodiscard]] size_t predecessor(const size_t seg) const
    {
      if (not contains(seg))
        return SIZE_MAX;
 
      const Geom_Number &label = nodes_(seg)->label;
      const Node *pred = nullptr;
      Node *cur = root_;
      while (cur != nullptr)
        if (cur->label < label)
          {
            pred = cur;
            cur = cur->right;
          }
        else
          cur = cur->left;
 
      return pred == nullptr ? SIZE_MAX : pred->seg;
    }
 
    [[nodiscard]] size_t successor(const size_t seg) const
    {
      if (not contains(seg))
        return SIZE_MAX;
 
      const Geom_Number &label = nodes_(seg)->label;
      const Node *succ = nullptr;
      Node *cur = root_;
      while (cur != nullptr)
        if (label < cur->label)
          {
            succ = cur;
            cur = cur->left;
          }
        else
          cur = cur->right;
 
      return succ == nullptr ? SIZE_MAX : succ->seg;
    }
  };
 
  static void check_and_enqueue(const Array<Segment> &segs,
                                const size_t i,
                                const size_t j,
                                const Geom_Number &sx,
                                LineSweepFramework<Event, EventLess> &eq,
                                DynSetTree<size_t, Treap_Rk> &seen_pairs,
                                const size_t n)
  {
    const size_t lo = i < j ? i : j;
    const size_t hi = i < j ? j : i;
    const size_t key = lo * n + hi;
    if (seen_pairs.search(key) != nullptr)
      return;
 
    const Segment &sa = segs(lo);
    const Segment &sb = segs(hi);
    const auto hit = segment_segment_intersection(sa, sb);
    if (not hit.intersects())
      return;
 
    if (hit.kind == SegmentSegmentIntersection::Kind::OVERLAP)
      {
        seen_pairs.insert(key);
        const Point overlap_start = hit.overlap.get_src_point();
        const Point overlap_end = hit.overlap.get_tgt_point();
        if (not (overlap_start.get_x() < sx))
          eq.enqueue(Event{overlap_start, EventType::INTERSECTION, lo, hi});
        if (not (overlap_end.get_x() < sx))
          eq.enqueue(Event{overlap_end, EventType::INTERSECTION, lo, hi});
        return;
      }
 
    const Point ip = hit.point;
    if (ip.get_x() < sx)
      return;  // Intersection is to the left of the sweep.
 
    seen_pairs.insert(key);
    eq.enqueue(Event{ip, EventType::INTERSECTION, lo, hi});
  }
 
public:
  [[nodiscard]] Array<Intersection> operator () (const Array<Segment> &segments) const
  {
    const size_t n = segments.size();
    Array<Intersection> result;
 
    if (n < 2)
      return result;
 
    // Canonicalize: src is the left endpoint.
    Array<Segment> segs;
    segs.reserve(n);
    for (size_t i = 0; i < n; ++i)
      {
        ah_domain_error_if(segments(i).get_src_point() == segments(i).get_tgt_point())
          << "Segment " << i << " is degenerate (zero length)";
        segs.append(canonicalize(segments(i)));
      }
 
    // Build the initial event queue (left + right endpoints).
    LineSweepFramework<Event, EventLess> eq;
    for (size_t i = 0; i < n; ++i)
      {
        eq.enqueue(Event{segs(i).get_src_point(), EventType::LEFT, i, 0});
        eq.enqueue(Event{segs(i).get_tgt_point(), EventType::RIGHT, i, 0});
      }
 
    // Seen intersection pairs (key = lo * n + hi).
    DynSetTree<size_t, Treap_Rk> seen_pairs;
    DynSetTree<size_t, Treap_Rk> reported_pairs;
 
    auto pair_key = [n](const size_t i, const size_t j)
      {
        const size_t lo = i < j ? i : j;
        const size_t hi = i < j ? j : i;
        return lo * n + hi;
      };
 
    auto append_intersection =
      [&result, &reported_pairs, &pair_key](const size_t i, const size_t j, const Point &p)
      {
        const size_t key = pair_key(i, j);
        if (reported_pairs.search(key) != nullptr)
          return;
        reported_pairs.insert(key);
 
        const size_t lo = i < j ? i : j;
        const size_t hi = i < j ? j : i;
        result.append(Intersection{lo, hi, p});
      };
 
    // Sweep-line status: balanced tree with O(log n) updates.
    StatusTree status(segs);
 
    while (eq.has_events())
      {
        const Event ev = eq.dequeue();
        const Geom_Number sx = ev.pt.get_x();
 
        if (ev.type == EventType::LEFT)
          {
            const size_t idx = ev.seg_a;
            status.insert(idx, sx);
 
            if (const size_t pred = status.predecessor(idx); pred != SIZE_MAX)
              check_and_enqueue(segs, pred, idx, sx, eq, seen_pairs, n);
            if (const size_t succ = status.successor(idx); succ != SIZE_MAX)
              check_and_enqueue(segs, idx, succ, sx, eq, seen_pairs, n);
          }
        else if (ev.type == EventType::RIGHT)
          {
            if (const size_t idx = ev.seg_a; status.contains(idx))
              {
                const size_t pred = status.predecessor(idx);
                const size_t succ = status.successor(idx);
                if (pred != SIZE_MAX and succ != SIZE_MAX)
                  check_and_enqueue(segs, pred, succ, sx, eq, seen_pairs, n);
                status.erase(idx);
              }
          }
        else  // INTERSECTION
          {
            const size_t a = ev.seg_a;
            const size_t b = ev.seg_b;
            append_intersection(a, b, ev.pt);
 
            // Walk outward from a (or b) through the status tree to find
            // all active segments passing through ev.pt.  Segments sharing
            // a point are adjacent in sweep-line order, so this is O(k)
            // instead of the former O(n) scan.
            Array<size_t> block;
 
            // Pick a seed segment that is still in the status tree
            size_t seed = SIZE_MAX;
            if (status.contains(a) and segs(a).contains(ev.pt))
              seed = a;
            else if (status.contains(b) and segs(b).contains(ev.pt))
              seed = b;
 
            if (seed != SIZE_MAX)
              {
                block.append(seed);
 
                // Walk predecessors
                for (size_t p = status.predecessor(seed); p != SIZE_MAX and segs(p).contains(ev.pt);
                     p = status.predecessor(p))
                  block.append(p);
 
                // Walk successors
                for (size_t s = status.successor(seed); s != SIZE_MAX and segs(s).contains(ev.pt);
                     s = status.successor(s))
                  block.append(s);
              }
 
            if (block.size() > 2)
              {
                for (size_t i = 0; i + 1 < block.size(); ++i)
                  for (size_t j = i + 1; j < block.size(); ++j)
                    append_intersection(block(i), block(j), ev.pt);
              }
 
            if (block.size() == 0)
              {
                if (status.contains(a))
                  block.append(a);
                if (status.contains(b) and (block.size() == 0 or block(0) != b))
                  block.append(b);
              }
 
            for (size_t i = 0; i < block.size(); ++i)
              status.erase(block(i));
            for (size_t i = 0; i < block.size(); ++i)
              status.insert(block(i), sx);
 
            for (size_t i = 0; i < block.size(); ++i)
              {
                const size_t s = block(i);
                if (const size_t pred = status.predecessor(s); pred != SIZE_MAX)
                  check_and_enqueue(segs, pred, s, sx, eq, seen_pairs, n);
                if (const size_t succ = status.successor(s); succ != SIZE_MAX)
                  check_and_enqueue(segs, s, succ, sx, eq, seen_pairs, n);
              }
          }
      }
 
    // Sort results by (x, y).
    quicksort_op(result, [](const Intersection &a, const Intersection &b)
      {
        if (a.point.get_x() != b.point.get_x())
          return a.point.get_x() < b.point.get_x();
        if (a.point.get_y() != b.point.get_y())
          return a.point.get_y() < b.point.get_y();
        if (a.seg_i != b.seg_i)
          return a.seg_i < b.seg_i;
        return a.seg_j < b.seg_j;
      });
 
    return result;
  }
};
 
// ============================================================================
// Monotone Polygon Triangulation
// ============================================================================
 
class MonotonePolygonTriangulation
{
private:
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &p)
  {
    return GeomPolygonUtils::extract_vertices(p);
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Array<Point> &v)
  {
    return GeomPolygonUtils::signed_double_area(v);
  }
 
  static void ensure_ccw(Array<Point> &v)
  {
    GeomPolygonUtils::ensure_ccw(v);
  }
 
  enum class VertexType
  {
    START,
    END,
    SPLIT,
    MERGE,
    REGULAR
  };
 
  [[nodiscard]] static bool is_above(const Point &a, const Point &b)
  {
    return a.get_y() > b.get_y() or (a.get_y() == b.get_y() and a.get_x() < b.get_x());
  }
 
  [[nodiscard]] static bool is_below(const Point &a, const Point &b)
  {
    return is_above(b, a);
  }
 
  [[nodiscard]] static bool edge_goes_down(const Array<Point> &verts, const size_t edge)
  {
    return is_below(verts((edge + 1) % verts.size()), verts(edge));
  }
 
  [[nodiscard]] static Geom_Number edge_x_at_y(const Array<Point> &verts,
                                               const size_t edge,
                                               const Geom_Number &y)
  {
    const Point &a = verts(edge);
    const Point &b = verts((edge + 1) % verts.size());
    if (a.get_y() == b.get_y())
      return a.get_x() < b.get_x() ? a.get_x() : b.get_x();
 
    return a.get_x() + (y - a.get_y()) * (b.get_x() - a.get_x()) / (b.get_y() - a.get_y());
  }
 
  [[nodiscard]] static bool edge_status_less(const size_t lhs,
                                             const size_t rhs,
                                             const Geom_Number &sweep_y,
                                             const Array<Point> &verts)
  {
    if (lhs == rhs)
      return false;
 
    const Geom_Number xl = edge_x_at_y(verts, lhs, sweep_y);
    const Geom_Number xr = edge_x_at_y(verts, rhs, sweep_y);
    if (xl != xr)
      return xl < xr;
    return lhs < rhs;
  }
 
  class EdgeStatusTree
  {
    struct Node
    {
      size_t edge;
      Geom_Number label;
      unsigned priority;
      Node *left = nullptr;
      Node *right = nullptr;
    };
 
    Node *root_ = nullptr;
    const Array<Point> &verts_;
    std::mt19937 rng_{0x31415926u};
    Array<Node *> nodes_;
 
    static void split_by_label(Node *root, const Geom_Number &label, Node *&left, Node *&right)
    {
      if (root == nullptr)
        {
          left = nullptr;
          right = nullptr;
          return;
        }
 
      if (root->label < label)
        {
          split_by_label(root->right, label, root->right, right);
          left = root;
        }
      else
        {
          split_by_label(root->left, label, left, root->left);
          right = root;
        }
    }
 
    [[nodiscard]] static Node *merge(Node *a, Node *b)
    {
      if (a == nullptr)
        return b;
      if (b == nullptr)
        return a;
      if (a->priority < b->priority)
        {
          a->right = merge(a->right, b);
          return a;
        }
      b->left = merge(a, b->left);
      return b;
    }
 
    [[nodiscard]] static Node *insert_by_label(Node *root, Node *node)
    {
      if (root == nullptr)
        return node;
 
      if (node->priority < root->priority)
        {
          Node *left = nullptr;
          Node *right = nullptr;
          split_by_label(root, node->label, left, right);
          node->left = left;
          node->right = right;
          return node;
        }
 
      if (node->label < root->label)
        root->left = insert_by_label(root->left, node);
      else
        root->right = insert_by_label(root->right, node);
      return root;
    }
 
    [[nodiscard]] static Node *erase_by_label(Node *root, const Geom_Number &label, Node *&removed)
    {
      if (root == nullptr)
        return nullptr;
 
      if (label < root->label)
        {
          root->left = erase_by_label(root->left, label, removed);
          return root;
        }
 
      if (root->label < label)
        {
          root->right = erase_by_label(root->right, label, removed);
          return root;
        }
 
      removed = root;
      return merge(root->left, root->right);
    }
 
    static void destroy(const Node *n)
    {
      if (n == nullptr)
        return;
      destroy(n->left);
      destroy(n->right);
      delete n;
    }
 
    [[nodiscard]] size_t predecessor_for_insert(const size_t edge, const Geom_Number &sweep_y) const
    {
      size_t pred = SIZE_MAX;
      const Node *cur = root_;
      while (cur != nullptr)
        if (edge_status_less(cur->edge, edge, sweep_y, verts_))
          {
            pred = cur->edge;
            cur = cur->right;
          }
        else
          cur = cur->left;
      return pred;
    }
 
    [[nodiscard]] size_t successor_for_insert(const size_t edge, const Geom_Number &sweep_y) const
    {
      size_t succ = SIZE_MAX;
      const Node *cur = root_;
      while (cur != nullptr)
        if (edge_status_less(edge, cur->edge, sweep_y, verts_))
          {
            succ = cur->edge;
            cur = cur->left;
          }
        else
          cur = cur->right;
      return succ;
    }
 
    [[nodiscard]] Geom_Number fresh_label_between(const size_t pred, const size_t succ) const
    {
      if (pred != SIZE_MAX and succ != SIZE_MAX)
        return (nodes_(pred)->label + nodes_(succ)->label) / Geom_Number(2);
      if (pred != SIZE_MAX)
        return nodes_(pred)->label + Geom_Number(1);
      if (succ != SIZE_MAX)
        return nodes_(succ)->label - Geom_Number(1);
      return {0};
    }
 
  public:
    explicit EdgeStatusTree(const Array<Point> &verts) : verts_(verts)
    {
      nodes_.reserve(verts.size());
      for (size_t i = 0; i < verts.size(); ++i)
        nodes_.append(nullptr);
    }
 
    ~EdgeStatusTree()
    {
      destroy(root_);
    }
 
    [[nodiscard]] bool contains(const size_t edge) const
    {
      return nodes_(edge) != nullptr;
    }
 
    void insert(const size_t edge, const Geom_Number &sweep_y)
    {
      if (contains(edge))
        return;
 
      const size_t pred = predecessor_for_insert(edge, sweep_y);
      const size_t succ = successor_for_insert(edge, sweep_y);
      const auto node = new Node{edge, fresh_label_between(pred, succ),
                                 static_cast<unsigned>(rng_()), nullptr, nullptr};
      root_ = insert_by_label(root_, node);
      nodes_(edge) = node;
    }
 
    void erase(const size_t edge)
    {
      if (not contains(edge))
        return;
 
      Node *removed = nullptr;
      root_ = erase_by_label(root_, nodes_(edge)->label, removed);
      nodes_(edge) = nullptr;
      delete removed;
    }
 
    [[nodiscard]] size_t left_edge_of_point(const Point &p, const Geom_Number &sweep_y) const
    {
      size_t best = SIZE_MAX;
      const Node *cur = root_;
      while (cur != nullptr)
        {
          const Geom_Number x = edge_x_at_y(verts_, cur->edge, sweep_y);
          if (x < p.get_x())
            {
              best = cur->edge;
              cur = cur->right;
            }
          else
            cur = cur->left;
        }
      return best;
    }
  };
 
  [[nodiscard]] static DynList<Triangle> triangulate_monotone(const Array<Point> &verts)
  {
    DynList<Triangle> result;
    const size_t n = verts.size();
    if (n < 3)
      return result;
    if (n == 3)
      {
        result.append(Triangle(verts(0), verts(1), verts(2)));
        return result;
      }
 
    // Sort vertex indices by y descending, x ascending for ties.
    Array<size_t> sorted;
    sorted.reserve(n);
    for (size_t i = 0; i < n; ++i)
      sorted.append(i);
 
    quicksort_op(sorted, [&verts](const size_t a, const size_t b)
      {
        if (verts(a).get_y() != verts(b).get_y())
          return verts(a).get_y() > verts(b).get_y();
        return verts(a).get_x() < verts(b).get_x();
      });
 
    // Identify left and right chains.
    // Top vertex = sorted(0), bottom vertex = sorted(n-1).
    // Left chain: goes from top to bottom counter-clockwise.
    const size_t top = sorted(0);
    const size_t bot = sorted(n - 1);
 
    Array<bool> on_left;
    on_left.reserve(n);
    for (size_t i = 0; i < n; ++i)
      on_left.append(false);
 
    // Walk from top to bottom going forward in the polygon.
    for (size_t i = top; i != bot; i = (i + 1) % n)
      on_left(i) = true;
    on_left(top) = true;  // top is on both; mark left.
 
    // Stack-based triangulation.
    FixedStack<size_t> stack(n);
    stack.push(sorted(0));
    stack.push(sorted(1));
 
    for (size_t i = 2; i < n - 1; ++i)
      {
        const size_t curr = sorted(i);
        const size_t stk_top = stack.top();
        if (on_left(curr) != on_left(stk_top))
          {
            // Different chain: fan triangles from curr to all stack vertices.
            while (stack.size() > 1)
              {
                const size_t a = stack.top();
                const size_t b = stack.top(1);
                result.append(Triangle(verts(curr), verts(a), verts(b)));
                stack.pop();
              }
            stack.pop();
            stack.push(sorted(i - 1));
            stack.push(curr);
          }
        else
          {
            // Same chain: pop vertices while diagonal is inside.
            size_t last_popped = stack.top();
            stack.pop();
 
            while (not stack.is_empty())
              {
                const size_t peek = stack.top();
                const Geom_Number area =
                  area_of_parallelogram(verts(curr), verts(last_popped), verts(peek));
 
                // On the left chain we need CW turn (area < 0);
                // on the right chain we need CCW turn (area > 0).
                if ((on_left(curr) and area >= 0) or (not on_left(curr) and area <= 0))
                  break;
 
                result.append(Triangle(verts(curr), verts(last_popped), verts(peek)));
                last_popped = peek;
                stack.pop();
              }
 
            stack.push(last_popped);
            stack.push(curr);
          }
      }
 
    // Process last vertex (bottom): fan to the remaining stack.
    const size_t last = sorted(n - 1);
    while (stack.size() > 1)
      {
        const size_t a = stack.top();
        const size_t b = stack.top(1);
        result.append(Triangle(verts(last), verts(a), verts(b)));
        stack.pop();
      }
 
    return result;
  }
 
  [[nodiscard]] static VertexType classify_vertex(const Array<Point> &v, const size_t i)
  {
    const size_t n = v.size();
    const Point &prev = v((i + n - 1) % n);
    const Point &curr = v(i);
    const Point &next = v((i + 1) % n);
 
    const bool prev_below = is_below(prev, curr);
    const bool next_below = is_below(next, curr);
    const bool prev_above = is_above(prev, curr);
    const bool next_above = is_above(next, curr);
    const bool reflex = orientation(prev, curr, next) == Orientation::CW;
 
    if (prev_below and next_below)
      return reflex ? VertexType::SPLIT : VertexType::START;
    if (prev_above and next_above)
      return reflex ? VertexType::MERGE : VertexType::END;
    return VertexType::REGULAR;
  }
 
  [[nodiscard]] static bool regular_interior_right(const Array<Point> &v, const size_t i)
  {
    return is_below(v((i + 1) % v.size()), v(i));
  }
 
  [[nodiscard]] static Array<Array<size_t>> build_faces_from_diagonals(
    const Array<Point> &verts,
    const DynSetTree<std::pair<size_t, size_t>> &diagonals)
  {
    const size_t n = verts.size();
    Array<Array<size_t>> adj;
    adj.reserve(n);
    for (size_t i = 0; i < n; ++i)
      adj.append(Array<size_t>());
 
    auto add_undirected_edge = [&adj](const size_t a, const size_t b)
      {
        adj(a).append(b);
        adj(b).append(a);
      };
 
    for (size_t i = 0; i < n; ++i)
      add_undirected_edge(i, (i + 1) % n);
 
    for (const auto &d : diagonals)
      add_undirected_edge(d.first, d.second);
 
    for (size_t v = 0; v < n; ++v)
      {
        auto &nbrs = adj(v);
        in_place_sort(nbrs);
        in_place_unique(nbrs);
        in_place_sort(nbrs, [&verts, v](const size_t a, const size_t b)
          {
            const Geom_Number dax = verts(a).get_x() - verts(v).get_x();
            const Geom_Number day = verts(a).get_y() - verts(v).get_y();
            const Geom_Number dbx = verts(b).get_x() - verts(v).get_x();
            const Geom_Number dby = verts(b).get_y() - verts(v).get_y();
 
            const bool upper_a = day > 0 or (day == 0 and dax >= 0);
            const bool upper_b = dby > 0 or (dby == 0 and dbx >= 0);
            if (upper_a != upper_b)
              return upper_a > upper_b;
 
            if (const Geom_Number cross = dax * dby - day * dbx; cross != 0)
              return cross > 0;
 
            const Geom_Number da2 = dax * dax + day * day;
            const Geom_Number db2 = dbx * dbx + dby * dby;
            return da2 < db2;
          });
      }
 
    using HalfEdge = std::pair<size_t, size_t>;
    std::map<HalfEdge, HalfEdge> next_half;
    for (size_t v = 0; v < n; ++v)
      {
        const auto &nbrs = adj(v);
        if (nbrs.is_empty())
          continue;
        for (size_t k = 0; k < nbrs.size(); ++k)
          {
            const size_t u = nbrs(k);
            const size_t pred = nbrs((k + nbrs.size() - 1) % nbrs.size());
            next_half[HalfEdge{u, v}] = HalfEdge{v, pred};
          }
      }
 
    auto face_area2 = [&verts](const Array<size_t> &face)
      {
        Geom_Number area2 = 0;
        for (size_t i = 0; i < face.size(); ++i)
          {
            const Point &a = verts(face(i));
            const Point &b = verts(face((i + 1) % face.size()));
            area2 += a.get_x() * b.get_y() - a.get_y() * b.get_x();
          }
        return area2;
      };
 
    DynSetTree<HalfEdge> visited;
    Array<Array<size_t>> faces;
    for (const auto &[kv, _] : next_half)
      {
        const HalfEdge start = kv;
        if (visited.search(start) != nullptr)
          continue;
 
        HalfEdge cur = start;
        Array<size_t> face;
        while (visited.insert(cur) != nullptr)
          {
            face.append(cur.first);
            auto it_next = next_half.find(cur);
            if (it_next == next_half.end())
              {
                face.empty();
                break;
              }
            cur = it_next->second;
            if (cur == start)
              break;
          }
 
        if (face.is_empty() or cur != start or face.size() < 3)
          continue;
        if (face_area2(face) <= 0)
          continue;  // Ignore outer face / degenerate loops.
 
        Array<size_t> poly_idx;
        poly_idx.reserve(face.size());
        for (const size_t idx : face)
          poly_idx.append(idx);
        faces.append(poly_idx);
      }
 
    return faces;
  }
 
  [[nodiscard]] static Array<Array<size_t>> decompose_to_monotone_faces(const Array<Point> &verts)
  {
    const size_t n = verts.size();
    Array<Array<size_t>> faces;
 
    if (n < 3)
      return faces;
 
    if (is_y_monotone(verts))
      {
        Array<size_t> one;
        one.reserve(n);
        for (size_t i = 0; i < n; ++i)
          one.append(i);
        faces.append(one);
        return faces;
      }
 
    Array<VertexType> vtype;
    vtype.reserve(n);
    for (size_t i = 0; i < n; ++i)
      vtype.append(classify_vertex(verts, i));
 
    Array<size_t> order;
    order.reserve(n);
    for (size_t i = 0; i < n; ++i)
      order.append(i);
    quicksort_op(order, [&verts](const size_t a, const size_t b)
      {
        if (verts(a).get_y() != verts(b).get_y())
          return verts(a).get_y() > verts(b).get_y();
        return verts(a).get_x() < verts(b).get_x();
      });
 
    Array<size_t> helper;
    helper.reserve(n);
    for (size_t i = 0; i < n; ++i)
      helper.append(SIZE_MAX);
 
    EdgeStatusTree status(verts);
    DynSetTree<std::pair<size_t, size_t>> diagonals;
 
    auto add_diagonal = [&](const size_t a, const size_t b)
      {
        if (a == b or b == SIZE_MAX)
          return;
        if ((a + 1) % n == b or (b + 1) % n == a)
          return;
 
        const size_t lo = a < b ? a : b;
        const size_t hi = a < b ? b : a;
        diagonals.insert({lo, hi});
      };
 
    auto helper_is_merge = [&helper, &vtype](const size_t edge)
      {
        return helper(edge) != SIZE_MAX and vtype(helper(edge)) == VertexType::MERGE;
      };
 
    for (size_t oi = 0; oi < n; ++oi)
      {
        const size_t vi = order(oi);
        const size_t prev = (vi + n - 1) % n;
        const size_t e_prev = prev;  // edge prev -> vi
        const size_t e_curr = vi;    // edge vi -> next
        const Geom_Number sweep_y = verts(vi).get_y();
 
        switch (vtype(vi))
          {
          case VertexType::START:
            if (edge_goes_down(verts, e_curr))
              {
                status.insert(e_curr, sweep_y);
                helper(e_curr) = vi;
              }
            break;
 
          case VertexType::END:
            if (edge_goes_down(verts, e_prev))
              {
                if (helper_is_merge(e_prev))
                  add_diagonal(vi, helper(e_prev));
                status.erase(e_prev);
              }
            break;
 
          case VertexType::SPLIT:
            {
              if (const size_t left = status.left_edge_of_point(verts(vi), sweep_y); left != SIZE_MAX)
                {
                  add_diagonal(vi, helper(left));
                  helper(left) = vi;
                }
 
              if (edge_goes_down(verts, e_curr))
                {
                  status.insert(e_curr, sweep_y);
                  helper(e_curr) = vi;
                }
            }
            break;
 
          case VertexType::MERGE:
            if (edge_goes_down(verts, e_prev))
              {
                if (helper_is_merge(e_prev))
                  add_diagonal(vi, helper(e_prev));
                status.erase(e_prev);
              }
            if (const size_t left = status.left_edge_of_point(verts(vi), sweep_y); left != SIZE_MAX)
              {
                if (helper_is_merge(left))
                  add_diagonal(vi, helper(left));
                helper(left) = vi;
              }
            break;
 
          case VertexType::REGULAR:
            if (regular_interior_right(verts, vi))
              {
                if (edge_goes_down(verts, e_prev))
                  {
                    if (helper_is_merge(e_prev))
                      add_diagonal(vi, helper(e_prev));
                    status.erase(e_prev);
                  }
                if (edge_goes_down(verts, e_curr))
                  {
                    status.insert(e_curr, sweep_y);
                    helper(e_curr) = vi;
                  }
              }
            else if (const size_t left = status.left_edge_of_point(verts(vi), sweep_y);
                     left != SIZE_MAX)
              {
                if (helper_is_merge(left))
                  add_diagonal(vi, helper(left));
                helper(left) = vi;
              }
            break;
          }
      }
 
    faces = build_faces_from_diagonals(verts, diagonals);
    if (faces.size() == 0)
      {
        Array<size_t> one;
        one.reserve(n);
        for (size_t i = 0; i < n; ++i)
          one.append(i);
        faces.append(one);
      }
    return faces;
  }
 
public:
  [[nodiscard]] DynList<Triangle> operator () (Polygon p) const
  {
    ah_domain_error_if(not p.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(p.size() < 3) << "Polygon must have at least 3 vertices";
 
    Array<Point> verts = extract_vertices(p);
    ah_domain_error_if(signed_double_area(verts) == 0) << "Polygon is degenerate (zero area)";
 
    ensure_ccw(verts);
 
    // Check if the polygon is y-monotone.
    if (is_y_monotone(verts))
      return triangulate_monotone(verts);
 
    const Array<Array<size_t>> faces = decompose_to_monotone_faces(verts);
    DynList<Triangle> result;
    bool produced_any = false;
 
    for (size_t fi = 0; fi < faces.size(); ++fi)
      {
        if (faces(fi).size() < 3)
          continue;
 
        Array<Point> mono;
        mono.reserve(faces(fi).size());
        for (size_t i = 0; i < faces(fi).size(); ++i)
          mono.append(verts(faces(fi)(i)));
 
        if (signed_double_area(mono) == 0)
          continue;
        ensure_ccw(mono);
 
        DynList<Triangle> tris;
        if (is_y_monotone(mono))
          tris = triangulate_monotone(mono);
        else
          {
            // Defensive fallback for degenerate decomposition edge cases.
            Polygon piece;
            for (size_t i = 0; i < mono.size(); ++i)
              piece.add_vertex(mono(i));
            if (piece.size() >= 3)
              {
                piece.close();
                constexpr CuttingEarsTriangulation ears;
                tris = ears(piece);
              }
          }
 
        for (DynList<Triangle>::Iterator it(tris); it.has_curr(); it.next_ne())
          {
            result.append(it.get_curr());
            produced_any = true;
          }
      }
 
    if (produced_any)
      return result;
 
    // Conservative fallback if decomposition could not produce valid faces.
    constexpr CuttingEarsTriangulation ears;
    return ears(p);
  }
 
private:
  [[nodiscard]] static bool is_y_monotone(const Array<Point> &v)
  {
    const size_t n = v.size();
    if (n <= 3)
      return true;
 
    // Find topmost and bottommost vertices.
    size_t top_idx = 0;
    size_t bot_idx = 0;
    for (size_t i = 1; i < n; ++i)
      {
        if (v(i).get_y() > v(top_idx).get_y() or
            (v(i).get_y() == v(top_idx).get_y() and v(i).get_x() < v(top_idx).get_x()))
          top_idx = i;
 
        if (v(i).get_y() < v(bot_idx).get_y() or
            (v(i).get_y() == v(bot_idx).get_y() and v(i).get_x() > v(bot_idx).get_x()))
          bot_idx = i;
      }
 
    // Walk from top to bottom along the forward chain — y must be
    // non-increasing.
    for (size_t i = top_idx;;)
      {
        const size_t next = (i + 1) % n;
        if (next == bot_idx)
          break;
        if (v(next).get_y() > v(i).get_y())
          return false;
        i = next;
      }
 
    // Walk from top to bottom along the backward chain — y must be
    // non-increasing.
    for (size_t i = top_idx;;)
      {
        const size_t prev = (i + n - 1) % n;
        if (prev == bot_idx)
          break;
        if (v(prev).get_y() > v(i).get_y())
          return false;
        i = prev;
      }
 
    return true;
  }
};
 
// ============================================================================
// Minkowski Sum for Convex Polygons — O(n + m)
// ============================================================================
 
class MinkowskiSumConvex
{
private:
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &poly)
  {
    return GeomPolygonUtils::extract_vertices(poly);
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Array<Point> &v)
  {
    return GeomPolygonUtils::signed_double_area(v);
  }
 
  [[nodiscard]] static bool is_convex(const Array<Point> &verts)
  {
    if (verts.size() < 3)
      return false;
    return GeomPolygonUtils::is_convex(verts);
  }
 
  static Array<Point> normalize(Array<Point> v)
  {
    GeomPolygonUtils::ensure_ccw(v);
 
    // Find bottom-most vertex (min y, then min x).
    size_t bot = 0;
    for (size_t i = 1; i < v.size(); ++i)
      if (v(i).get_y() < v(bot).get_y() or
          (v(i).get_y() == v(bot).get_y() and v(i).get_x() < v(bot).get_x()))
        bot = i;
 
    Array<Point> result;
    result.reserve(v.size());
    for (size_t i = 0; i < v.size(); ++i)
      result.append(v((bot + i) % v.size()));
 
    return result;
  }
 
  [[nodiscard]] static Point edge_vec(const Array<Point> &v, const size_t i)
  {
    const size_t j = (i + 1) % v.size();
    return {v(j).get_x() - v(i).get_x(), v(j).get_y() - v(i).get_y()};
  }
 
  [[nodiscard]] static Geom_Number cross(const Point &a, const Point &b)
  {
    return a.get_x() * b.get_y() - a.get_y() * b.get_x();
  }
 
public:
  [[nodiscard]] Polygon operator () (const Polygon &P, const Polygon &Q) const
  {
    ah_domain_error_if(not P.is_closed()) << "First polygon must be closed";
    ah_domain_error_if(not Q.is_closed()) << "Second polygon must be closed";
    ah_domain_error_if(P.size() < 3) << "First polygon must have at least 3 vertices";
    ah_domain_error_if(Q.size() < 3) << "Second polygon must have at least 3 vertices";
 
    Array<Point> pv = extract_vertices(P);
    Array<Point> qv = extract_vertices(Q);
 
    ah_domain_error_if(not is_convex(pv)) << "First polygon must be convex";
    ah_domain_error_if(not is_convex(qv)) << "Second polygon must be convex";
 
    pv = normalize(pv);
    qv = normalize(qv);
 
    const size_t np = pv.size();
    const size_t nq = qv.size();
 
    Array<Point> result;
    result.reserve(np + nq);
 
    size_t ip = 0;
    size_t iq = 0;
 
    while (ip < np or iq < nq)
      {
        result.append(Point(pv(ip % np).get_x() + qv(iq % nq).get_x(),
                            pv(ip % np).get_y() + qv(iq % nq).get_y()));
 
        if (ip >= np)
          {
            ++iq;
            continue;
          }
        if (iq >= nq)
          {
            ++ip;
            continue;
          }
 
        const Point ep = edge_vec(pv, ip % np);
        const Point eq = edge_vec(qv, iq % nq);
 
        if (const Geom_Number cr = cross(ep, eq); cr > 0)
          ++ip;
        else if (cr < 0)
          ++iq;
        else
          {
            ++ip;
            ++iq;
          }  // Parallel edges: advance both.
      }
 
    // Remove collinear and duplicate vertices.
    Array<Point> clean;
    clean.reserve(result.size());
    for (size_t i = 0; i < result.size(); ++i)
      {
        if (clean.is_empty() or clean.get_last() != result(i))
          clean.append(result(i));
      }
    if (clean.size() > 1 and clean(0) == clean.get_last())
      static_cast<void>(clean.remove_last());
 
    Polygon ret;
    for (size_t i = 0; i < clean.size(); ++i)
      ret.add_vertex(clean(i));
 
    if (ret.size() >= 3)
      ret.close();
 
    return ret;
  }
};
 
// ============================================================================
// Convex Polygon Distance (GJK) — 2D
// ============================================================================
 
class ConvexPolygonDistanceGJK
{
public:
  struct Result
  {
    Geom_Number distance_squared = 0;  
    Geom_Number distance = 0;          
    Point closest_on_first;            
    Point closest_on_second;           
    bool intersects = false;           
    size_t gjk_iterations = 0;         
  };
 
private:
  struct SupportPoint
  {
    Point a;          
    Point b;          
    Point v;          
    double vx = 0.0;  
    double vy = 0.0;  
  };
 
  struct ClosestSimplexResult
  {
    std::vector<SupportPoint> reduced_simplex;
    double cx = 0.0;
    double cy = 0.0;
    Point witness_a;
    Point witness_b;
    bool contains_origin = false;
  };
 
  static constexpr size_t kMaxIters = 64;
  static constexpr double kEps = 1e-12;
 
  [[nodiscard]] static double to_double(const Geom_Number &v)
  {
    return geom_number_to_double(v);
  }
 
  [[nodiscard]] static double dot2(const double ax,
                                   const double ay,
                                   const double bx,
                                   const double by) noexcept
  {
    return ax * bx + ay * by;
  }
 
  [[nodiscard]] static double norm2(const double x, const double y) noexcept
  {
    return dot2(x, y, x, y);
  }
 
  [[nodiscard]] static Point point_from_double(const double x, const double y)
  {
    return {Geom_Number(x), Geom_Number(y)};
  }
 
  [[nodiscard]] static Point lerp_point(const Point &a, const Point &b, const double t)
  {
    const double ax = to_double(a.get_x());
    const double ay = to_double(a.get_y());
    const double bx = to_double(b.get_x());
    const double by = to_double(b.get_y());
    return point_from_double((1.0 - t) * ax + t * bx, (1.0 - t) * ay + t * by);
  }
 
  [[nodiscard]] static Point centroid_of(const Array<Point> &v)
  {
    Geom_Number sx = 0;
    Geom_Number sy = 0;
    for (size_t i = 0; i < v.size(); ++i)
      {
        sx += v(i).get_x();
        sy += v(i).get_y();
      }
    return {sx / Geom_Number(static_cast<long>(v.size())),
            sy / Geom_Number(static_cast<long>(v.size()))};
  }
 
  [[nodiscard]] static SupportPoint support(const Array<Point> &p,
                                            const Array<Point> &q,
                                            const double dx,
                                            const double dy)
  {
    size_t ip = 0;
    size_t iq = 0;
    double best_p = -std::numeric_limits<double>::infinity();
    double best_q = -std::numeric_limits<double>::infinity();
 
    for (size_t i = 0; i < p.size(); ++i)
      {
        const double proj = dot2(to_double(p(i).get_x()), to_double(p(i).get_y()), dx, dy);
        if (proj > best_p)
          {
            best_p = proj;
            ip = i;
          }
      }
 
    // Support of Minkowski difference uses opposite direction in q.
    for (size_t i = 0; i < q.size(); ++i)
      {
        const double proj = dot2(to_double(q(i).get_x()), to_double(q(i).get_y()), -dx, -dy);
        if (proj > best_q)
          {
            best_q = proj;
            iq = i;
          }
      }
 
    const Point &pa = p(ip);
    const Point &pb = q(iq);
    const Geom_Number vx = pa.get_x() - pb.get_x();
    const Geom_Number vy = pa.get_y() - pb.get_y();
    return SupportPoint{pa, pb, Point(vx, vy), to_double(vx), to_double(vy)};
  }
 
  [[nodiscard]] static bool polygons_intersect_or_contain(const Polygon &p, const Polygon &q)
  {
    for (Polygon::Segment_Iterator itp(p); itp.has_curr(); itp.next_ne())
      {
        const Segment sp = itp.get_current_segment();
        for (Polygon::Segment_Iterator itq(q); itq.has_curr(); itq.next_ne())
          if (sp.intersects_with(itq.get_current_segment()))
            return true;
      }
 
    Point vp;
    for (Polygon::Vertex_Iterator it(p); it.has_curr(); it.next_ne())
      {
        vp = it.get_current_vertex().to_point();
        break;
      }
 
    Point vq;
    for (Polygon::Vertex_Iterator it(q); it.has_curr(); it.next_ne())
      {
        vq = it.get_current_vertex().to_point();
        break;
      }
 
    return PointInPolygonWinding::contains(q, vp) or PointInPolygonWinding::contains(p, vq);
  }
 
  [[nodiscard]] static ClosestSimplexResult closest_from_simplex(const std::vector<SupportPoint> &simplex)
  {
    ah_domain_error_if(simplex.empty()) << "GJK simplex cannot be empty";
 
    ClosestSimplexResult out;
 
    if (simplex.size() == 1)
      {
        out.reduced_simplex = simplex;
        out.cx = simplex[0].vx;
        out.cy = simplex[0].vy;
        out.witness_a = simplex[0].a;
        out.witness_b = simplex[0].b;
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    if (simplex.size() == 2)
      {
        const SupportPoint &a = simplex[0];
        const SupportPoint &b = simplex[1];
        const double abx = b.vx - a.vx;
        const double aby = b.vy - a.vy;
        const double ab2 = norm2(abx, aby);
 
        if (ab2 <= kEps * kEps)
          {
            out.reduced_simplex = {a};
            out.cx = a.vx;
            out.cy = a.vy;
            out.witness_a = a.a;
            out.witness_b = a.b;
            out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
            return out;
          }
 
        double t = -dot2(a.vx, a.vy, abx, aby) / ab2;
        if (t < 0.0)
          t = 0.0;
        if (t > 1.0)
          t = 1.0;
 
        if (t <= kEps)
          {
            out.reduced_simplex = {a};
            out.cx = a.vx;
            out.cy = a.vy;
            out.witness_a = a.a;
            out.witness_b = a.b;
          }
        else if (t >= 1.0 - kEps)
          {
            out.reduced_simplex = {b};
            out.cx = b.vx;
            out.cy = b.vy;
            out.witness_a = b.a;
            out.witness_b = b.b;
          }
        else
          {
            out.reduced_simplex = {a, b};
            out.cx = a.vx + t * abx;
            out.cy = a.vy + t * aby;
            out.witness_a = lerp_point(a.a, b.a, t);
            out.witness_b = lerp_point(a.b, b.b, t);
          }
 
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    // Triangle case.
    const SupportPoint &a = simplex[0];
    const SupportPoint &b = simplex[1];
    const SupportPoint &c = simplex[2];
 
    const double abx = b.vx - a.vx;
    const double aby = b.vy - a.vy;
    const double acx = c.vx - a.vx;
    const double acy = c.vy - a.vy;
    const double apx = -a.vx;
    const double apy = -a.vy;
 
    const double d1 = dot2(abx, aby, apx, apy);
    const double d2 = dot2(acx, acy, apx, apy);
    if (d1 <= 0.0 and d2 <= 0.0)
      {
        out.reduced_simplex = {a};
        out.cx = a.vx;
        out.cy = a.vy;
        out.witness_a = a.a;
        out.witness_b = a.b;
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    const double bpx = -b.vx;
    const double bpy = -b.vy;
    const double d3 = dot2(abx, aby, bpx, bpy);
    const double d4 = dot2(acx, acy, bpx, bpy);
    if (d3 >= 0.0 and d4 <= d3)
      {
        out.reduced_simplex = {b};
        out.cx = b.vx;
        out.cy = b.vy;
        out.witness_a = b.a;
        out.witness_b = b.b;
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    const double vc = d1 * d4 - d3 * d2;
    if (vc <= 0.0 and d1 >= 0.0 and d3 <= 0.0)
      {
        const double t = d1 / (d1 - d3);
        out.reduced_simplex = {a, b};
        out.cx = a.vx + t * abx;
        out.cy = a.vy + t * aby;
        out.witness_a = lerp_point(a.a, b.a, t);
        out.witness_b = lerp_point(a.b, b.b, t);
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    const double cpx = -c.vx;
    const double cpy = -c.vy;
    const double d5 = dot2(abx, aby, cpx, cpy);
    const double d6 = dot2(acx, acy, cpx, cpy);
    if (d6 >= 0.0 and d5 <= d6)
      {
        out.reduced_simplex = {c};
        out.cx = c.vx;
        out.cy = c.vy;
        out.witness_a = c.a;
        out.witness_b = c.b;
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    const double vb = d5 * d2 - d1 * d6;
    if (vb <= 0.0 and d2 >= 0.0 and d6 <= 0.0)
      {
        const double t = d2 / (d2 - d6);
        out.reduced_simplex = {a, c};
        out.cx = a.vx + t * acx;
        out.cy = a.vy + t * acy;
        out.witness_a = lerp_point(a.a, c.a, t);
        out.witness_b = lerp_point(a.b, c.b, t);
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    const double va = d3 * d6 - d5 * d4;
    if (va <= 0.0 and d4 - d3 >= 0.0 and d5 - d6 >= 0.0)
      {
        const double t = (d4 - d3) / (d4 - d3 + (d5 - d6));
        const double bcx = c.vx - b.vx;
        const double bcy = c.vy - b.vy;
        out.reduced_simplex = {b, c};
        out.cx = b.vx + t * bcx;
        out.cy = b.vy + t * bcy;
        out.witness_a = lerp_point(b.a, c.a, t);
        out.witness_b = lerp_point(b.b, c.b, t);
        out.contains_origin = norm2(out.cx, out.cy) <= kEps * kEps;
        return out;
      }
 
    // Origin is inside triangle.
    const double denom = va + vb + vc;
    if (std::fabs(denom) <= kEps)
      {
        out.reduced_simplex = {a, b, c};
        out.cx = 0.0;
        out.cy = 0.0;
        out.witness_a = a.a;
        out.witness_b = a.b;
        out.contains_origin = true;
        return out;
      }
 
    const double inv = 1.0 / denom;
    const double wa = va * inv;
    const double wb = vb * inv;
    const double wc = vc * inv;
    out.reduced_simplex = {a, b, c};
    out.cx = 0.0;
    out.cy = 0.0;
    out.witness_a = point_from_double(
      wa * to_double(a.a.get_x()) + wb * to_double(b.a.get_x()) + wc * to_double(c.a.get_x()),
      wa * to_double(a.a.get_y()) + wb * to_double(b.a.get_y()) + wc * to_double(c.a.get_y()));
    out.witness_b = point_from_double(
      wa * to_double(a.b.get_x()) + wb * to_double(b.b.get_x()) + wc * to_double(c.b.get_x()),
      wa * to_double(a.b.get_y()) + wb * to_double(b.b.get_y()) + wc * to_double(c.b.get_y()));
    out.contains_origin = true;
    return out;
  }
 
  [[nodiscard]] static Result exact_refine_disjoint(const Polygon &p,
                                                    const Polygon &q,
                                                    const Array<Point> &pv,
                                                    const Array<Point> &qv)
  {
    Result out;
    out.intersects = false;
 
    if (polygons_intersect_or_contain(p, q))
      {
        out.distance_squared = 0;
        out.distance = 0;
        out.closest_on_first = pv(0);
        out.closest_on_second = pv(0);
        out.intersects = true;
        return out;
      }
 
    bool has_best = false;
    Geom_Number best_d2 = 0;
    Point best_a, best_b;
 
    for (size_t i = 0; i < pv.size(); ++i)
      {
        const Point &pnt = pv(i);
        for (size_t j = 0; j < qv.size(); ++j)
          {
            const Point &q0 = qv(j);
            const Point &q1 = qv((j + 1) % qv.size());
            const Segment edge(q0, q1);
            const Point proj = edge.project(pnt);
            if (const Geom_Number d2 = pnt.distance_squared_to(proj); not has_best or d2 < best_d2)
              {
                has_best = true;
                best_d2 = d2;
                best_a = pnt;
                best_b = proj;
              }
          }
      }
 
    for (size_t i = 0; i < qv.size(); ++i)
      {
        const Point &pnt = qv(i);
        for (size_t j = 0; j < pv.size(); ++j)
          {
            const Point &p0 = pv(j);
            const Point &p1 = pv((j + 1) % pv.size());
            const Segment edge(p0, p1);
            const Point proj = edge.project(pnt);
            if (const Geom_Number d2 = pnt.distance_squared_to(proj); not has_best or d2 < best_d2)
              {
                has_best = true;
                best_d2 = d2;
                best_a = proj;
                best_b = pnt;
              }
          }
      }
 
    ah_domain_error_if(not has_best) << "Could not compute distance between convex polygons";
 
    out.distance_squared = best_d2;
    out.distance = square_root(best_d2);
    out.closest_on_first = best_a;
    out.closest_on_second = best_b;
    out.intersects = (best_d2 == 0);
    return out;
  }
 
public:
  [[nodiscard]] Result operator () (const Polygon &p, const Polygon &q) const
  {
    ah_domain_error_if(not p.is_closed()) << "First polygon must be closed";
    ah_domain_error_if(not q.is_closed()) << "Second polygon must be closed";
    ah_domain_error_if(p.size() < 3) << "First polygon must have at least 3 vertices";
    ah_domain_error_if(q.size() < 3) << "Second polygon must have at least 3 vertices";
 
    const Array<Point> pv = GeomPolygonUtils::extract_vertices(p);
    const Array<Point> qv = GeomPolygonUtils::extract_vertices(q);
 
    ah_domain_error_if(not GeomPolygonUtils::is_convex(pv)) << "First polygon must be convex";
    ah_domain_error_if(not GeomPolygonUtils::is_convex(qv)) << "Second polygon must be convex";
 
    // Fast exact overlap check to avoid unnecessary iterations.
    if (polygons_intersect_or_contain(p, q))
      {
        Result r;
        r.distance_squared = 0;
        r.distance = 0;
        r.closest_on_first = pv(0);
        r.closest_on_second = pv(0);
        r.intersects = true;
        return r;
      }
 
    Point cp = centroid_of(pv);
    Point cq = centroid_of(qv);
    double dirx = to_double(cp.get_x() - cq.get_x());
    double diry = to_double(cp.get_y() - cq.get_y());
    if (norm2(dirx, diry) <= kEps * kEps)
      {
        dirx = 1.0;
        diry = 0.0;
      }
 
    std::vector<SupportPoint> simplex;
    simplex.reserve(3);
    simplex.push_back(support(pv, qv, dirx, diry));
    dirx = -simplex[0].vx;
    diry = -simplex[0].vy;
 
    double prev_d2 = std::numeric_limits<double>::infinity();
    size_t iters = 0;
 
    for (; iters < kMaxIters; ++iters)
      {
        if (norm2(dirx, diry) <= kEps * kEps)
          break;
 
        simplex.push_back(support(pv, qv, dirx, diry));
        if (simplex.size() > 3)
          simplex.erase(simplex.begin());
 
        ClosestSimplexResult step = closest_from_simplex(simplex);
        simplex = std::move(step.reduced_simplex);
 
        const double d2 = norm2(step.cx, step.cy);
        if (step.contains_origin or d2 <= kEps * kEps)
          {
            Result r;
            r.distance_squared = 0;
            r.distance = 0;
            r.closest_on_first = step.witness_a;
            r.closest_on_second = step.witness_b;
            r.intersects = true;
            r.gjk_iterations = iters + 1;
            return r;
          }
 
        if (prev_d2 - d2 <= kEps * std::max(1.0, prev_d2))
          break;
 
        prev_d2 = d2;
        dirx = -step.cx;
        diry = -step.cy;
      }
 
    Result refined = exact_refine_disjoint(p, q, pv, qv);
    refined.gjk_iterations = iters;
    return refined;
  }
};
 
// ============================================================================
// KD-Tree Point Search — O(log n) Nearest Neighbor
// ============================================================================
 
class KDTreePointSearch
{
  K2Tree<> tree;
  Array<Point> points_;
  Rectangle bounds_;
 
  [[nodiscard]] static bool lexicographic_less(const Point &a, const Point &b)
  {
    if (a.get_x() < b.get_x())
      return true;
    if (b.get_x() < a.get_x())
      return false;
    return a.get_y() < b.get_y();
  }
 
  [[nodiscard]] static Array<Point> unique_points(Array<Point> points)
  {
    quicksort_op(points, [](const Point &a, const Point &b)
      {
        return lexicographic_less(a, b);
      });
    Array<Point> uniq;
    uniq.reserve(points.size());
    for (size_t i = 0; i < points.size(); ++i)
      if (uniq.is_empty() or uniq.get_last() != points(i))
        uniq.append(points(i));
    return uniq;
  }
 
public:
  struct DebugPartition
  {
    Rectangle region;                    
    bool split_on_x = true;              
    Geom_Number split_value = 0;         
    size_t depth = 0;                    
    bool is_leaf = false;                
    Point representative = Point(0, 0);  
  };
 
  struct DebugSnapshot
  {
    Rectangle bounds;                  
    Array<Point> points;               
    Array<DebugPartition> partitions;  
  };
 
  KDTreePointSearch(const Geom_Number &xmin,
                    const Geom_Number &ymin,
                    const Geom_Number &xmax,
                    const Geom_Number &ymax)
    : tree(xmin, ymin, xmax, ymax), bounds_(xmin, ymin, xmax, ymax)
  {}
 
  [[nodiscard]] static KDTreePointSearch build(const Array<Point> &points,
                                               const Geom_Number &xmin,
                                               const Geom_Number &ymin,
                                               const Geom_Number &xmax,
                                               const Geom_Number &ymax)
  {
    KDTreePointSearch kd(xmin, ymin, xmax, ymax);
    kd.tree = K2Tree<>::build(points, Point(xmin, ymin), Point(xmax, ymax));
    kd.points_ = unique_points(points);
    return kd;
  }
 
  bool insert(const Point &p)
  {
    if (not tree.insert(p))
      return false;
    points_.append(p);
    return true;
  }
 
  [[nodiscard]] bool contains(const Point &p) const
  {
    return tree.contains(p);
  }
 
  [[nodiscard]] std::optional<Point> nearest(const Point &p) const
  {
    return tree.nearest(p);
  }
 
  void range(const Geom_Number &xmin,
             const Geom_Number &ymin,
             const Geom_Number &xmax,
             const Geom_Number &ymax,
             DynList<Point> *out) const
  {
    tree.range({xmin, ymin, xmax, ymax}, out);
  }
 
  [[nodiscard]] size_t size() const noexcept
  {
    return tree.size();
  }
 
  [[nodiscard]] bool is_empty() const noexcept
  {
    return tree.is_empty();
  }
 
  template <typename Op>
  void for_each(Op &&op) const
  {
    tree.for_each(std::forward<Op>(op));
  }
 
  [[nodiscard]] DebugSnapshot debug_snapshot() const
  {
    DebugSnapshot snap;
    snap.bounds = bounds_;
    snap.points = points_;
    if (points_.is_empty())
      return snap;
 
    auto recurse = [&](const auto &self, const Array<Point> &pts, const Rectangle &region,
                       const size_t depth, const bool split_on_x) -> void
      {
        if (pts.is_empty())
          return;
 
        Array<Point> sorted = pts;
        quicksort_op(sorted, [split_on_x](const Point &a, const Point &b)
          {
            if (split_on_x)
              {
                if (a.get_x() != b.get_x())
                  return a.get_x() < b.get_x();
                return a.get_y() < b.get_y();
              }
            if (a.get_y() != b.get_y())
              return a.get_y() < b.get_y();
            return a.get_x() < b.get_x();
          });
 
        size_t mid = sorted.size() / 2;
        if (mid == 0)
          mid = 1;
        if (mid >= sorted.size())
          mid = sorted.size() - 1;
 
        const Point pivot = sorted(mid);
        DebugPartition part;
        part.region = region;
        part.split_on_x = split_on_x;
        part.split_value = split_on_x ? pivot.get_x() : pivot.get_y();
        part.depth = depth;
        part.is_leaf = sorted.size() == 1;
        part.representative = pivot;
        snap.partitions.append(part);
 
        if (sorted.size() == 1)
          return;
 
        Array<Point> left_pts;
        Array<Point> right_pts;
        left_pts.reserve(mid);
        right_pts.reserve(sorted.size() - mid);
        for (size_t i = 0; i < mid; ++i)
          left_pts.append(sorted(i));
        for (size_t i = mid; i < sorted.size(); ++i)
          right_pts.append(sorted(i));
 
        if (split_on_x)
          {
            Rectangle left(region.get_xmin(), region.get_ymin(), pivot.get_x(), region.get_ymax());
            Rectangle right(pivot.get_x(), region.get_ymin(), region.get_xmax(), region.get_ymax());
            self(self, left_pts, left, depth + 1, false);
            self(self, right_pts, right, depth + 1, false);
          }
        else
          {
            Rectangle bottom(region.get_xmin(), region.get_ymin(), region.get_xmax(), pivot.get_y());
            Rectangle top(region.get_xmin(), pivot.get_y(), region.get_xmax(), region.get_ymax());
            self(self, left_pts, bottom, depth + 1, true);
            self(self, right_pts, top, depth + 1, true);
          }
      };
 
    recurse(recurse, points_, bounds_, 0, true);
    return snap;
  }
};
 
// ============================================================================
// Convex Polygon Decomposition — Hertel-Mehlhorn
// ============================================================================
 
class ConvexPolygonDecomposition
{
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  [[nodiscard]] static size_t find_pos(const Array<size_t> &face, size_t v)
  {
    for (size_t i = 0; i < face.size(); ++i)
      if (face(i) == v)
        return i;
    return NONE;
  }
 
  [[nodiscard]] static bool is_polygon_edge(size_t u, size_t v, size_t n)
  {
    if (u > v)
      {
        const size_t tmp = u;
        u = v;
        v = tmp;
      }
    return v == u + 1 or (u == 0 and v == n - 1);
  }
 
  [[nodiscard]] static bool can_merge(const Array<Point> &pts,
                                      const Array<size_t> &f1,
                                      const Array<size_t> &f2,
                                      size_t u,
                                      size_t v)
  {
    const size_t n1 = f1.size();
    const size_t n2 = f2.size();
 
    size_t pu1 = find_pos(f1, u);
    size_t pv1 = find_pos(f1, v);
 
    // Ensure u is followed by v in f1 (CCW).  If not, swap roles.
    if ((pu1 + 1) % n1 != pv1)
      {
        const size_t tmp = u;
        u = v;
        v = tmp;
        pu1 = find_pos(f1, u);
        pv1 = find_pos(f1, v);
      }
 
    const size_t prev_u = f1((pu1 + n1 - 1) % n1);
    const size_t next_v = f1((pv1 + 1) % n1);
 
    const size_t pu2 = find_pos(f2, u);
    const size_t pv2 = find_pos(f2, v);
 
    const size_t next_u = f2((pu2 + 1) % n2);
    const size_t prev_v = f2((pv2 + n2 - 1) % n2);
 
    if (orientation(pts(prev_u), pts(u), pts(next_u)) == Orientation::CW)
      return false;
    if (orientation(pts(prev_v), pts(v), pts(next_v)) == Orientation::CW)
      return false;
 
    return true;
  }
 
  [[nodiscard]] static Array<size_t> merge_faces(const Array<size_t> &f1,
                                                 const Array<size_t> &f2,
                                                 size_t u,
                                                 size_t v)
  {
    const size_t n1 = f1.size();
    const size_t n2 = f2.size();
 
    size_t pu1 = find_pos(f1, u);
    size_t pv1 = find_pos(f1, v);
 
    if ((pu1 + 1) % n1 != pv1)
      {
        const size_t tmp = u;
        u = v;
        v = tmp;
        pv1 = find_pos(f1, v);
      }
 
    const size_t pu2 = find_pos(f2, u);
 
    Array<size_t> merged;
    merged.reserve(n1 + n2 - 2);
 
    // Part 1: f1 vertices from after v around to u (inclusive), skip v.
    for (size_t k = 0; k < n1 - 1; ++k)
      merged.append(f1((pv1 + 1 + k) % n1));
 
    // Part 2: f2 vertices from after u around to v (inclusive), skip u.
    for (size_t k = 0; k < n2 - 1; ++k)
      merged.append(f2((pu2 + 1 + k) % n2));
 
    return merged;
  }
 
  [[nodiscard]] static Array<Point> extract_vertices(const Polygon &p)
  {
    return GeomPolygonUtils::extract_vertices(p);
  }
 
public:
  [[nodiscard]] Array<Polygon> operator () (const Polygon &poly) const
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(poly.size() < 3) << "Polygon must have >= 3 vertices";
 
    const Array<Point> pts = extract_vertices(poly);
    const size_t n = pts.size();
 
    if (n == 3)
      {
        Array<Polygon> result;
        result.append(poly);
        return result;
      }
 
    // Triangulate.
    MonotonePolygonTriangulation triang;
    DynList<Triangle> tri_list = triang(poly);
 
    // Build indexed faces from triangles.
    Array<Array<size_t>> faces;
    for (DynList<Triangle>::Iterator it(tri_list); it.has_curr(); it.next_ne())
      {
        const Triangle &t = it.get_curr();
        size_t i0 = NONE, i1 = NONE, i2 = NONE;
        for (size_t i = 0; i < n; ++i)
          {
            if (i0 == NONE and pts(i) == t.get_p1())
              i0 = i;
            if (i1 == NONE and pts(i) == t.get_p2())
              i1 = i;
            if (i2 == NONE and pts(i) == t.get_p3())
              i2 = i;
          }
        if (i0 == NONE or i1 == NONE or i2 == NONE)
          continue;
 
        if (orientation(pts(i0), pts(i1), pts(i2)) == Orientation::CW)
          {
            const size_t tmp = i1;
            i1 = i2;
            i2 = tmp;
          }
 
        Array<size_t> face;
        face.append(i0);
        face.append(i1);
        face.append(i2);
        faces.append(std::move(face));
      }
 
    // Hertel-Mehlhorn: greedily merge across diagonals.
    bool changed = true;
    while (changed)
      {
        changed = false;
        for (size_t fi = 0; fi < faces.size() and not changed; ++fi)
          {
            const auto f1 = faces(fi);  // copy to avoid dangling when faces mutates
            for (size_t k = 0; k < f1.size() and not changed; ++k)
              {
                const size_t u = f1(k);
                const size_t v = f1((k + 1) % f1.size());
 
                if (is_polygon_edge(u, v, n))
                  continue;
 
                for (size_t fj = fi + 1; fj < faces.size() and not changed; ++fj)
                  {
                    const auto f2 = faces(fj);  // copy for the same reason
                    if (find_pos(f2, u) == NONE or find_pos(f2, v) == NONE)
                      continue;
 
                    if (not can_merge(pts, f1, f2, u, v))
                      continue;
 
                    Array<size_t> merged = merge_faces(f1, f2, u, v);
 
                    Array<Array<size_t>> new_faces;
                    new_faces.reserve(faces.size() - 1);
                    for (size_t i = 0; i < faces.size(); ++i)
                      {
                        if (i == fi)
                          new_faces.append(std::move(merged));
                        else if (i != fj)
                          new_faces.append(std::move(faces(i)));
                      }
                    faces = std::move(new_faces);
                    changed = true;
                  }
              }
          }
      }
 
    // Convert index faces to Polygons.
    Array<Polygon> result;
    result.reserve(faces.size());
    for (size_t fi = 0; fi < faces.size(); ++fi)
      {
        Polygon p;
        for (size_t k = 0; k < faces(fi).size(); ++k)
          p.add_vertex(pts(faces(fi)(k)));
        if (p.size() >= 3)
          {
            p.close();
            result.append(std::move(p));
          }
      }
 
    return result;
  }
};
 
// ============================================================================
// Range Tree 2D — Orthogonal Range Queries
// ============================================================================
 
class RangeTree2D
{
public:
  struct DebugNode
  {
    size_t tree_index = 0;                   
    size_t lo = 0;                           
    size_t hi = 0;                           
    size_t left = ~static_cast<size_t>(0);   
    size_t right = ~static_cast<size_t>(0);  
    Geom_Number xmin = 0;                    
    Geom_Number xmax = 0;                    
    Geom_Number split_x = 0;                 
    size_t y_sorted_size = 0;  
    bool is_leaf = false;      
  };
 
  struct DebugSnapshot
  {
    Array<Point> x_sorted_points;  
    Array<DebugNode> nodes;        
  };
 
private:
  struct Node
  {
    Array<Point> y_sorted;  
  };
 
  Array<Point> pts_;  
  Array<Node> tree_;  
  size_t n_ = 0;
  bool built_ = false;
 
  [[nodiscard]] static size_t lower_bound_y(const Array<Point> &arr, const Geom_Number &ymin)
  {
    size_t lo = 0, hi = arr.size();
    while (lo < hi)
      if (const size_t mid = lo + (hi - lo) / 2; arr(mid).get_y() < ymin)
        lo = mid + 1;
      else
        hi = mid;
    return lo;
  }
 
  [[nodiscard]] static size_t upper_bound_y(const Array<Point> &arr, const Geom_Number &ymax)
  {
    size_t lo = 0, hi = arr.size();
    while (lo < hi)
      if (const size_t mid = lo + (hi - lo) / 2; arr(mid).get_y() <= ymax)
        lo = mid + 1;
      else
        hi = mid;
    return lo;
  }
 
  [[nodiscard]] size_t lower_bound_x(const Geom_Number &xval) const
  {
    size_t lo = 0, hi = n_;
    while (lo < hi)
      if (const size_t mid = lo + (hi - lo) / 2; pts_(mid).get_x() < xval)
        lo = mid + 1;
      else
        hi = mid;
    return lo;
  }
 
  [[nodiscard]] size_t upper_bound_x(const Geom_Number &xval) const
  {
    size_t lo = 0, hi = n_;
    while (lo < hi)
      if (const size_t mid = lo + (hi - lo) / 2; pts_(mid).get_x() <= xval)
        lo = mid + 1;
      else
        hi = mid;
    return lo;
  }
 
  void build_node(const size_t node, const size_t lo, const size_t hi)
  {
    if (lo == hi)
      {
        tree_(node).y_sorted.append(pts_(lo));
        return;
      }
 
    const size_t mid = lo + (hi - lo) / 2;
    build_node(2 * node, lo, mid);
    build_node(2 * node + 1, mid + 1, hi);
 
    // Merge children's y-sorted arrays.
    const auto &left = tree_(2 * node).y_sorted;
    const auto &right = tree_(2 * node + 1).y_sorted;
    auto &merged = tree_(node).y_sorted;
    merged.reserve(left.size() + right.size());
 
    size_t i = 0, j = 0;
    while (i < left.size() and j < right.size())
      if (left(i).get_y() < right(j).get_y() or
          (left(i).get_y() == right(j).get_y() && left(i).get_x() <= right(j).get_x()))
        merged.append(left(i++));
      else
        merged.append(right(j++));
    while (i < left.size())
      merged.append(left(i++));
    while (j < right.size())
      merged.append(right(j++));
  }
 
  void query_range(const size_t node,
                   const size_t lo,
                   const size_t hi,
                   const size_t qlo,
                   const size_t qhi,
                   const Geom_Number &ymin,
                   const Geom_Number &ymax,
                   DynList<Point> &out) const
  {
    if (qlo > qhi or lo > qhi or hi < qlo)
      return;
 
    if (qlo <= lo and hi <= qhi)
      {
        const auto &ys = tree_(node).y_sorted;
        const size_t from = lower_bound_y(ys, ymin);
        const size_t to = upper_bound_y(ys, ymax);
        for (size_t i = from; i < to; ++i)
          out.append(ys(i));
        return;
      }
 
    const size_t mid = lo + (hi - lo) / 2;
    query_range(2 * node, lo, mid, qlo, qhi, ymin, ymax, out);
    query_range(2 * node + 1, mid + 1, hi, qlo, qhi, ymin, ymax, out);
  }
 
public:
  void build(const DynList<Point> &points)
  {
    pts_ = Array<Point>();
    for (DynList<Point>::Iterator it(points); it.has_curr(); it.next_ne())
      pts_.append(it.get_curr());
 
    n_ = pts_.size();
    if (n_ == 0)
      {
        built_ = true;
        return;
      }
 
    quicksort_op(pts_, [](const Point &a, const Point &b)
      {
        return a.get_x() < b.get_x() || (a.get_x() == b.get_x() and a.get_y() < b.get_y());
      });
 
    tree_ = Array<Node>();
    const size_t tree_sz = 4 * n_ + 4;
    tree_.reserve(tree_sz);
    for (size_t i = 0; i < tree_sz; ++i)
      tree_.append(Node{Array<Point>()});
 
    build_node(1, 0, n_ - 1);
    built_ = true;
  }
 
  [[nodiscard]] DynList<Point> query(const Geom_Number &xmin,
                                     const Geom_Number &xmax,
                                     const Geom_Number &ymin,
                                     const Geom_Number &ymax) const
  {
    DynList<Point> out;
    if (not built_ or n_ == 0)
      return out;
 
    const size_t qlo = lower_bound_x(xmin);
    const size_t qhi = upper_bound_x(xmax);
    if (qhi == 0)
      return out;
 
    query_range(1, 0, n_ - 1, qlo, qhi - 1, ymin, ymax, out);
    return out;
  }
 
  [[nodiscard]] size_t size() const noexcept
  {
    return n_;
  }
 
  [[nodiscard]] bool is_empty() const noexcept
  {
    return n_ == 0;
  }
 
  [[nodiscard]] DebugSnapshot debug_snapshot() const
  {
    DebugSnapshot snap;
    snap.x_sorted_points = pts_;
    if (not built_ or n_ == 0)
      return snap;
 
    // A binary range tree with n leaves has exactly 2n - 1 snapshot nodes.
    // Reserving also avoids needless reallocations while the snapshot is built.
    const size_t max_size = std::numeric_limits<size_t>::max();
    if (n_ <= max_size / 2 + 1)
      snap.nodes.reserve(n_ + (n_ - 1));
 
    auto build_debug = [&](const auto &self, const size_t tree_idx, const size_t lo,
                           const size_t hi) -> size_t
      {
        const size_t out_idx = snap.nodes.size();
        snap.nodes.append(DebugNode{});
        snap.nodes(out_idx).tree_index = tree_idx;
        snap.nodes(out_idx).lo = lo;
        snap.nodes(out_idx).hi = hi;
        snap.nodes(out_idx).is_leaf = lo == hi;
        snap.nodes(out_idx).xmin = pts_(lo).get_x();
        snap.nodes(out_idx).xmax = pts_(hi).get_x();
        snap.nodes(out_idx).y_sorted_size = tree_(tree_idx).y_sorted.size();
        snap.nodes(out_idx).split_x = pts_((lo + hi) / 2).get_x();
 
        if (lo < hi)
          {
            const size_t mid = lo + (hi - lo) / 2;
            const size_t left = self(self, 2 * tree_idx, lo, mid);
            const size_t right = self(self, 2 * tree_idx + 1, mid + 1, hi);
            snap.nodes(out_idx).left = left;
            snap.nodes(out_idx).right = right;
          }
 
        return out_idx;
      };
 
    build_debug(build_debug, 1, 0, n_ - 1);
    return snap;
  }
};
 
// ============================================================================
// Convex Polygon Offset (Inward / Outward)
// ============================================================================
 
class ConvexPolygonOffset
{
  friend class PolygonOffset;
 
  [[nodiscard]] static Array<Point> extract_verts(const Polygon &poly)
  {
    return GeomPolygonUtils::extract_vertices(poly);
  }
 
  [[nodiscard]] static Geom_Number signed_double_area(const Array<Point> &v)
  {
    return GeomPolygonUtils::signed_double_area(v);
  }
 
  [[nodiscard]] static bool is_convex(const Array<Point> &v)
  {
    if (v.size() < 3)
      return false;
    return GeomPolygonUtils::is_convex(v);
  }
 
  static void ensure_ccw(Array<Point> &v)
  {
    GeomPolygonUtils::ensure_ccw(v);
  }
 
  static void offset_edge(const Point &a,
                          const Point &b,
                          const Geom_Number &d,
                          const bool inward,
                          Point &oa,
                          Point &ob)
  {
    const mpfr_class dx(b.get_x() - a.get_x());
    const mpfr_class dy(b.get_y() - a.get_y());
    const mpfr_class len = hypot(dx, dy);
    const mpfr_class md(d);
 
    // For CCW polygon: inward normal = (dy, -dx)/len, outward = (-dy, dx)/len
    mpfr_class nx, ny;
    if (inward)
      {
        nx = -dy * md / len;
        ny = dx * md / len;
      }
    else
      {
        nx = dy * md / len;
        ny = -dx * md / len;
      }
 
    oa = Point(Geom_Number(mpfr_class(a.get_x()) + nx), Geom_Number(mpfr_class(a.get_y()) + ny));
    ob = Point(Geom_Number(mpfr_class(b.get_x()) + nx), Geom_Number(mpfr_class(b.get_y()) + ny));
  }
 
  [[nodiscard]] static Point line_intersect(const Point &a1,
                                            const Point &a2,
                                            const Point &b1,
                                            const Point &b2)
  {
    const Geom_Number &a1x = a1.get_x(), &a1y = a1.get_y();
    const Geom_Number &a2x = a2.get_x(), &a2y = a2.get_y();
    const Geom_Number &b1x = b1.get_x(), &b1y = b1.get_y();
    const Geom_Number &b2x = b2.get_x(), &b2y = b2.get_y();
 
    const Geom_Number dax = a2x - a1x, day = a2y - a1y;
    const Geom_Number dbx = b2x - b1x, dby = b2y - b1y;
    const Geom_Number denom = dax * dby - day * dbx;
    if (denom == 0)
      {
        // Consecutive offset lines can be parallel when the input has a
        // collinear triple. In that case, use the shared shifted vertex.
        return a2;
      }
 
    const Geom_Number t = ((b1x - a1x) * dby - (b1y - a1y) * dbx) / denom;
    return {a1x + t * dax, a1y + t * day};
  }
 
public:
  static Polygon inward(const Polygon &convex_poly, const Geom_Number &distance)
  {
    ah_domain_error_if(not convex_poly.is_closed()) << "Polygon must be closed";
 
    Array<Point> v = extract_verts(convex_poly);
 
    ah_domain_error_if(v.size() < 3) << "Polygon must have >= 3 vertices";
    ah_domain_error_if(not is_convex(v)) << "Polygon must be convex";
 
    if (distance == 0)
      return convex_poly;
 
    ensure_ccw(v);
    const size_t n = v.size();
 
    Array<HalfPlaneIntersection::HalfPlane> hps;
    hps.reserve(n);
 
    for (size_t i = 0; i < n; ++i)
      {
        const size_t j = (i + 1) % n;
        Point oa, ob;
        offset_edge(v(i), v(j), distance, true, oa, ob);
        hps.append(HalfPlaneIntersection::HalfPlane(oa, ob));
      }
 
    constexpr HalfPlaneIntersection hpi;
    return hpi(hps);
  }
 
  static Polygon outward(const Polygon &convex_poly, const Geom_Number &distance)
  {
    ah_domain_error_if(not convex_poly.is_closed()) << "Polygon must be closed";
 
    Array<Point> v = extract_verts(convex_poly);
 
    ah_domain_error_if(v.size() < 3) << "Polygon must have >= 3 vertices";
    ah_domain_error_if(not is_convex(v)) << "Polygon must be convex";
 
    if (distance == 0)
      return convex_poly;
 
    ensure_ccw(v);
    const size_t n = v.size();
 
    // Compute offset lines for each edge.
    Array<Point> oa, ob;  // offset edge endpoints
    oa.reserve(n);
    ob.reserve(n);
    for (size_t i = 0; i < n; ++i)
      {
        Point a, b;
        offset_edge(v(i), v((i + 1) % n), distance, false, a, b);
        oa.append(a);
        ob.append(b);
      }
 
    // Intersect consecutive offset lines → new vertices.
    Polygon result;
    for (size_t i = 0; i < n; ++i)
      {
        const size_t j = (i + 1) % n;
        const Geom_Number dax = ob(i).get_x() - oa(i).get_x();
        const Geom_Number day = ob(i).get_y() - oa(i).get_y();
        const Geom_Number dbx = ob(j).get_x() - oa(j).get_x();
        const Geom_Number dby = ob(j).get_y() - oa(j).get_y();
        if (const Geom_Number denom = dax * dby - day * dbx; denom == 0)
          // Collinear triples produce consecutive parallel offset lines:
          // there is no corner vertex to add for that junction.
          continue;
 
        result.add_vertex(line_intersect(oa(i), ob(i), oa(j), ob(j)));
      }
    if (result.size() >= 3)
      result.close();
    return result;
  }
};
 
// ============================================================================
// General Polygon Offset (non-convex)
// ============================================================================
 
class PolygonOffset
{
public:
  enum class JoinType
  {
    Miter,  
    Bevel   
  };
 
  struct Result
  {
    Array<Polygon> polygons;  
 
    [[nodiscard]] bool is_empty() const noexcept
    {
      return polygons.is_empty();
    }
 
    [[nodiscard]] size_t size() const noexcept
    {
      return polygons.size();
    }
  };
 
  [[nodiscard]] Result operator () (const Polygon &poly,
                                    const Geom_Number &distance,
                                    const JoinType join = JoinType::Miter,
                                    const Geom_Number &miter_limit = Geom_Number(2)) const
  {
    ah_domain_error_if(not poly.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(poly.size() < 3) << "Polygon must have >= 3 vertices";
 
    if (distance == 0)
      {
        Result r;
        r.polygons.append(poly);
        return r;
      }
 
    Array<Point> v = GeomPolygonUtils::extract_vertices(poly);
    GeomPolygonUtils::ensure_ccw(v);
 
    const Array<Point> raw = compute_raw_offset(v, distance, join, miter_limit);
 
    if (raw.size() < 3)
      return Result{};
 
    return cleanup(raw);
  }
 
  [[nodiscard]] Polygon offset_polygon(const Polygon &poly,
                                       const Geom_Number &distance,
                                       JoinType join = JoinType::Miter,
                                       const Geom_Number &miter_limit = Geom_Number(2)) const
  {
    Result r = (*this)(poly, distance, join, miter_limit);
    if (r.is_empty())
      return {};
 
    size_t best = 0;
    Geom_Number best_area = abs_area(r.polygons(0));
    for (size_t i = 1; i < r.polygons.size(); ++i)
      if (const Geom_Number a = abs_area(r.polygons(i)); a > best_area)
        {
          best_area = a;
          best = i;
        }
    return r.polygons(best);
  }
 
private:
  // ----- helpers -----
 
  [[nodiscard]] static Geom_Number abs_area(const Polygon &p)
  {
    Geom_Number a = GeomPolygonUtils::signed_double_area(p);
    if (a < 0)
      a = -a;
    return a;
  }
 
  static void offset_edge(const Point &a,
                          const Point &b,
                          const Geom_Number &d,
                          const bool inward,
                          Point &oa,
                          Point &ob)
  {
    ConvexPolygonOffset::offset_edge(a, b, d, inward, oa, ob);
  }
 
  [[nodiscard]] static Point line_intersect(const Point &a1,
                                            const Point &a2,
                                            const Point &b1,
                                            const Point &b2)
  {
    return ConvexPolygonOffset::line_intersect(a1, a2, b1, b2);
  }
 
  // ----- Phase 1: raw offset polygon -----
 
  [[nodiscard]] static Geom_Number sq_dist(const Point &a, const Point &b)
  {
    const Geom_Number dx = b.get_x() - a.get_x();
    const Geom_Number dy = b.get_y() - a.get_y();
    return dx * dx + dy * dy;
  }
 
  [[nodiscard]] static Array<Point> compute_raw_offset(const Array<Point> &v,
                                                       const Geom_Number &distance,
                                                       const JoinType join,
                                                       const Geom_Number &miter_limit)
  {
    const size_t n = v.size();
    const bool inward = distance < 0;
    Geom_Number d = distance;
    if (inward)
      d = -distance;
 
    // Compute offset edge pairs.
    Array<Point> oa, ob;
    oa.reserve(n);
    ob.reserve(n);
    for (size_t i = 0; i < n; ++i)
      {
        Point a, b;
        offset_edge(v(i), v((i + 1) % n), d, inward, a, b);
        oa.append(a);
        ob.append(b);
      }
 
    // Join consecutive offset edges, tracking junction boundaries.
    const Geom_Number miter_sq = miter_limit * miter_limit * d * d;
    Array<Point> raw;
    raw.reserve(n * 2);
 
    // junction_first[i] = index in raw where junction i's vertices begin.
    // junction_count[i] = number of vertices emitted for junction i.
    Array<size_t> junction_first, junction_count;
    junction_first.reserve(n);
    junction_count.reserve(n);
 
    for (size_t i = 0; i < n; ++i)
      {
        const size_t j = (i + 1) % n;
        junction_first.append(raw.size());
 
        const Geom_Number dax = ob(i).get_x() - oa(i).get_x();
        const Geom_Number day = ob(i).get_y() - oa(i).get_y();
        const Geom_Number dbx = ob(j).get_x() - oa(j).get_x();
        const Geom_Number dby = ob(j).get_y() - oa(j).get_y();
 
        if (const Geom_Number denom = dax * dby - day * dbx; denom == 0)
          {
            junction_count.append(0);
            continue;
          }
 
        if (const Point miter = line_intersect(oa(i), ob(i), oa(j), ob(j)); join == JoinType::Bevel or
            (join == JoinType::Miter && sq_dist(v((i + 1) % n), miter) > miter_sq))
          {
            raw.append(ob(i));
            raw.append(oa(j));
            junction_count.append(2);
          }
        else
          {
            raw.append(miter);
            junction_count.append(1);
          }
      }
 
    // Validate edge directions: for each span between consecutive
    // junctions, the direction must match the corresponding original edge.
    // A reversed direction indicates that the offset has "crossed through"
    // the polygon (excessive offset).
    for (size_t i = 0; i < n; ++i)
      {
        const size_t j = (i + 1) % n;
        if (junction_count(i) == 0 || junction_count(j) == 0)
          continue;
 
        // Span runs from the last vertex of junction i to the first
        // vertex of junction j, along offset edge (i+1)%n.
        const size_t span_start = junction_first(i) + junction_count(i) - 1;
        const size_t span_end = junction_first(j);
 
        const Geom_Number sdx = raw(span_end).get_x() - raw(span_start).get_x();
        const Geom_Number sdy = raw(span_end).get_y() - raw(span_start).get_y();
 
        // Direction of original edge (i+1)%n: v(j) → v((j+1)%n).
        const Geom_Number edx = v((j + 1) % n).get_x() - v(j).get_x();
        const Geom_Number edy = v((j + 1) % n).get_y() - v(j).get_y();
 
        if (sdx * edx + sdy * edy < 0)
          return {};  // direction reversed → excessive offset
      }
 
    return raw;
  }
 
  // ----- Phase 2: self-intersection cleanup -----
 
  struct Intersection
  {
    Point pt;
    size_t edge_i, edge_j;
    Geom_Number alpha_i, alpha_j;  // parameter along each edge
  };
 
  struct AugVertex
  {
    Point pt;
    bool is_intersection = false;
    size_t partner = SIZE_MAX;  // index of same point on other edge
    bool visited = false;
    Geom_Number alpha = 0;
  };
 
  [[nodiscard]] static Geom_Number edge_param(const Point &P, const Point &Q, const Point &I)
  {
    if (const Geom_Number dx = Q.get_x() - P.get_x(); dx != 0)
      return (I.get_x() - P.get_x()) / dx;
    return (I.get_y() - P.get_y()) / (Q.get_y() - P.get_y());
  }
 
  [[nodiscard]] static Array<Intersection> find_self_intersections(const Array<Point> &raw)
  {
    const size_t n = raw.size();
    Array<Intersection> isects;
 
    for (size_t i = 0; i < n; ++i)
      {
        const Point &a0 = raw(i);
        const Point &a1 = raw((i + 1) % n);
        const Segment sa(a0, a1);
 
        for (size_t j = i + 2; j < n; ++j)
          {
            // Skip adjacent edges (they share a vertex).
            if (j == (i + n - 1) % n)
              continue;
            if (i == 0 && j == n - 1)
              continue;
 
            const Point &b0 = raw(j);
            const Point &b1 = raw((j + 1) % n);
            const Segment sb(b0, b1);
 
            if (not sa.intersects_properly_with(sb))
              continue;
 
            const Point ip = sa.intersection_with(sb);
            const Geom_Number ai = edge_param(a0, a1, ip);
            const Geom_Number aj = edge_param(b0, b1, ip);
            isects.append({ip, i, j, ai, aj});
          }
      }
 
    return isects;
  }
 
  static void sort_by_alpha(Array<size_t> &idx, const Array<Geom_Number> &keys)
  {
    for (size_t i = 1; i < idx.size(); ++i)
      {
        const size_t val = idx(i);
        const Geom_Number &key = keys(val);
        size_t j = i;
        while (j > 0 && keys(idx(j - 1)) > key)
          {
            idx(j) = idx(j - 1);
            --j;
          }
        idx(j) = val;
      }
  }
 
  [[nodiscard]] static Array<AugVertex> build_augmented(const Array<Point> &raw,
                                                        const Array<Intersection> &isects)
  {
    const size_t n = raw.size();
    const size_t m = isects.size();
 
    // Position in the augmented list for each intersection occurrence.
    // Each intersection appears twice (once on each edge).
    Array<size_t> pos_i, pos_j;
    pos_i.reserve(m);
    pos_j.reserve(m);
    for (size_t k = 0; k < m; ++k)
      {
        pos_i.append(0);
        pos_j.append(0);
      }
 
    Array<AugVertex> aug;
    aug.reserve(n + 2 * m);
 
    for (size_t i = 0; i < n; ++i)
      {
        // Append original vertex.
        AugVertex v;
        v.pt = raw(i);
        aug.append(v);
 
        // Collect intersections on this edge.
        Array<size_t> edge_isects;
        Array<Geom_Number> edge_alphas;
        for (size_t k = 0; k < m; ++k)
          {
            if (isects(k).edge_i == i)
              {
                edge_isects.append(k);
                edge_alphas.append(isects(k).alpha_i);
              }
            else if (isects(k).edge_j == i)
              {
                edge_isects.append(k);
                edge_alphas.append(isects(k).alpha_j);
              }
          }
 
        if (edge_isects.is_empty())
          continue;
 
        // Sort by alpha.
        Array<size_t> order;
        for (size_t p = 0; p < edge_isects.size(); ++p)
          order.append(p);
        sort_by_alpha(order, edge_alphas);
 
        for (size_t p = 0; p < order.size(); ++p)
          {
            const size_t k = edge_isects(order(p));
            const size_t aug_idx = aug.size();
 
            // Record position for partner linking.
            if (isects(k).edge_i == i)
              pos_i(k) = aug_idx;
            else
              pos_j(k) = aug_idx;
 
            AugVertex iv;
            iv.pt = isects(k).pt;
            iv.is_intersection = true;
            iv.alpha = edge_alphas(order(p));
            aug.append(iv);
          }
      }
 
    // Set partner links.
    for (size_t k = 0; k < m; ++k)
      {
        aug(pos_i(k)).partner = pos_j(k);
        aug(pos_j(k)).partner = pos_i(k);
      }
 
    return aug;
  }
 
  [[nodiscard]] static Polygon build_poly(const Array<Point> &pts)
  {
    Polygon p;
    for (size_t i = 0; i < pts.size(); ++i)
      p.add_vertex(pts(i));
    if (pts.size() >= 3)
      p.close();
    return p;
  }
 
  [[nodiscard]] static Array<Polygon> extract_contours(Array<AugVertex> &aug)
  {
    Array<Polygon> result;
    const size_t N = aug.size();
    const size_t safety = N * 2 + 10;
 
    for (size_t s = 0; s < N; ++s)
      {
        if (not aug(s).is_intersection || aug(s).visited)
          continue;
 
        // Trace one contour starting from intersection s.
        // Jump to partner first, then walk forward.
        Array<Point> boundary;
        size_t steps = 0;
 
        aug(s).visited = true;
        if (aug(s).partner != SIZE_MAX)
          aug(aug(s).partner).visited = true;
 
        // Jump to partner to enter the "other branch".
        size_t idx = (aug(s).partner != SIZE_MAX) ? aug(s).partner : s;
        const size_t entry = idx;  // we'll loop until we return here
 
        do
          {
            // Append current vertex and walk forward.
            boundary.append(aug(idx).pt);
            idx = (idx + 1) % N;
 
            while (not aug(idx).is_intersection)
              {
                boundary.append(aug(idx).pt);
                idx = (idx + 1) % N;
                if (++steps > safety)
                  goto done_contour;
              }
 
            // At the next intersection — mark visited and jump to partner.
            aug(idx).visited = true;
            if (aug(idx).partner != SIZE_MAX)
              {
                aug(aug(idx).partner).visited = true;
                idx = aug(idx).partner;
              }
 
            if (++steps > safety)
              break;
        } while (idx != entry);
 
      done_contour:
        if (boundary.size() >= 3)
          {
            // Keep only CCW contours (positive signed area).
            if (const Geom_Number sa = GeomPolygonUtils::signed_double_area(boundary); sa > 0)
              result.append(build_poly(boundary));
          }
      }
 
    return result;
  }
 
  static Result cleanup(const Array<Point> &raw)
  {
    const auto isects = find_self_intersections(raw);
 
    if (isects.is_empty())
      {
        // No self-intersections — check if the raw polygon is valid CCW.
        const Geom_Number sa = GeomPolygonUtils::signed_double_area(raw);
        Result r;
        if (sa > 0 && raw.size() >= 3)
          r.polygons.append(build_poly(raw));
        return r;
      }
 
    auto aug = build_augmented(raw, isects);
    Result r;
    r.polygons = extract_contours(aug);
    return r;
  }
};
 
// ============================================================================
// Visibility Polygon
// ============================================================================
 
class VisibilityPolygon
{
  [[nodiscard]] static int angle_quadrant(const Geom_Number &dx, const Geom_Number &dy)
  {
    if (dx > 0 and dy >= 0)
      return 0;
    if (dx <= 0 and dy > 0)
      return 1;
    if (dx < 0 and dy <= 0)
      return 2;
    return 3;  // dx >= 0 and dy < 0
  }
 
  [[nodiscard]] static bool angle_less(const Point &q, const Point &a, const Point &b)
  {
    const Geom_Number dax = a.get_x() - q.get_x();
    const Geom_Number day = a.get_y() - q.get_y();
    const Geom_Number dbx = b.get_x() - q.get_x();
    const Geom_Number dby = b.get_y() - q.get_y();
 
    const int qa = angle_quadrant(dax, day);
    const int qb = angle_quadrant(dbx, dby);
    if (qa != qb)
      return qa < qb;
 
    // Same quadrant: cross product.  Positive = a is before b (CCW).
    if (const Geom_Number cross = dax * dby - day * dbx; cross != 0)
      return cross > 0;
 
    // Same angle: closer point first.
    return dax * dax + day * day < (dbx * dbx + dby * dby);
  }
 
  [[nodiscard]] static Geom_Number ray_param(const Point &q,
                                             const Point &dir,
                                             const Point &e0,
                                             const Point &e1)
  {
    const Geom_Number rdx = dir.get_x() - q.get_x();
    const Geom_Number rdy = dir.get_y() - q.get_y();
    const Geom_Number edx = e1.get_x() - e0.get_x();
    const Geom_Number edy = e1.get_y() - e0.get_y();
    const Geom_Number denom = rdx * edy - rdy * edx;
    if (denom == 0)
      return {-1};
 
    const Geom_Number dx = e0.get_x() - q.get_x();
    const Geom_Number dy = e0.get_y() - q.get_y();
    const Geom_Number t = (dx * edy - dy * edx) / denom;
    const Geom_Number s = (dx * rdy - dy * rdx) / denom;
    if (s < 0 or s > 1 or t < 0)
      return {-1};
    return t;
  }
 
  [[nodiscard]] static Point ray_edge_hit(const Point &q,
                                          const Point &dir,
                                          const Point &e0,
                                          const Point &e1)
  {
    const Geom_Number t = ray_param(q, dir, e0, e1);
    const Geom_Number rdx = dir.get_x() - q.get_x();
    const Geom_Number rdy = dir.get_y() - q.get_y();
    return {q.get_x() + t * rdx, q.get_y() + t * rdy};
  }
 
  class EdgeStatusTree
  {
    struct EdgeKey
    {
      Geom_Number t;
      size_t edge;
    };
 
    struct EdgeKeyCmp
    {
      bool operator () (const EdgeKey &a, const EdgeKey &b) const
      {
        if (a.t != b.t)
          return a.t < b.t;
        return a.edge < b.edge;
      }
    };
 
    DynSetTree<EdgeKey, Treap, EdgeKeyCmp> tree_;
    Array<Geom_Number> params_;  // edge → ray_param at insertion time
    Array<bool> in_tree_;        // edge → currently in tree
    const Array<Point> &verts_;
    const size_t n_;
    const Point &query_;
 
  public:
    EdgeStatusTree(const Array<Point> &verts, const size_t n, const Point &query)
      : verts_(verts), n_(n), query_(query)
    {
      for (size_t i = 0; i < n; ++i)
        {
          params_.append(Geom_Number(-1));
          in_tree_.append(false);
        }
    }
 
    void insert(const size_t edge, const Point &dir)
    {
      if (in_tree_(edge))
        return;
 
      const Geom_Number t = ray_param(query_, dir, verts_(edge), verts_((edge + 1) % n_));
      params_(edge) = t;
      in_tree_(edge) = true;
      tree_.insert(EdgeKey{t, edge});
    }
 
    void erase(const size_t edge)
    {
      if (not in_tree_(edge))
        return;
 
      tree_.remove(EdgeKey{params_(edge), edge});
      in_tree_(edge) = false;
    }
 
    [[nodiscard]] size_t min() const
    {
      if (tree_.is_empty())
        return n_;
      return tree_.min().edge;
    }
 
    [[nodiscard]] bool contains(const size_t edge) const
    {
      return in_tree_(edge);
    }
 
    [[nodiscard]] bool is_empty() const
    {
      return tree_.is_empty();
    }
  };
 
public:
  [[nodiscard]] Polygon operator () (const Polygon &polygon, const Point &query) const
  {
    ah_domain_error_if(not polygon.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(polygon.size() < 3) << "Polygon must have >= 3 vertices";
    ah_domain_error_if(not PointInPolygonWinding::strictly_contains(polygon, query))
      << "Query point must be strictly inside the polygon";
 
    // Extract vertices.
    Array<Point> verts;
    for (Polygon::Vertex_Iterator it(polygon); it.has_curr(); it.next_ne())
      verts.append(it.get_current_vertex());
    const size_t n = verts.size();
 
    // Sort vertex indices by angle from query.
    Array<size_t> order;
    order.reserve(n);
    for (size_t i = 0; i < n; ++i)
      order.append(i);
    quicksort_op(order, [&](size_t a, size_t b)
      {
        return angle_less(query, verts(a), verts(b));
      });
 
    // Determine which edges cross the initial ray (wrapping edges).
    // Their angular span straddles 0°, so their start/end events must be
    // swapped relative to non-wrapping edges.
    const Point init_dir(query.get_x() + 1, query.get_y());
    Array<bool> wrapping;
    wrapping.reserve(n);
    for (size_t ei = 0; ei < n; ++ei)
      {
        const Geom_Number t = ray_param(query, init_dir, verts(ei), verts((ei + 1) % n));
        wrapping.append(t > 0);
      }
 
    // Build edge event tables: for each vertex, which edges start/end there.
    // Edge i goes from verts(i) to verts((i+1)%n).
    // For non-wrapping edges: insert at the smaller-angle vertex, remove at
    //   the larger-angle vertex (normal sweep order).
    // For wrapping edges (already in the initial status): remove at the
    //   smaller-angle vertex (ray exits their span), insert at the
    //   larger-angle vertex (ray re-enters their span).
    Array<DynList<size_t>> starts, ends;
    starts.reserve(n);
    ends.reserve(n);
    for (size_t i = 0; i < n; ++i)
      starts.append(DynList<size_t>());
    for (size_t i = 0; i < n; ++i)
      ends.append(DynList<size_t>());
 
    for (size_t ei = 0; ei < n; ++ei)
      {
        const size_t a = ei, b = (ei + 1) % n;
        const bool a_less = angle_less(query, verts(a), verts(b));
        const size_t small_v = a_less ? a : b;
        const size_t large_v = a_less ? b : a;
 
        if (wrapping(ei))
          {
            ends(small_v).append(ei);    // remove when ray exits span
            starts(large_v).append(ei);  // re-insert when ray re-enters
          }
        else
          {
            starts(small_v).append(ei);  // insert when ray enters span
            ends(large_v).append(ei);    // remove when ray exits span
          }
      }
 
    // Initialize status with wrapping edges.
    EdgeStatusTree status(verts, n, query);
    for (size_t ei = 0; ei < n; ++ei)
      if (wrapping(ei))
        status.insert(ei, init_dir);
 
    // Build visibility polygon.
    Array<Point> vis_pts;
 
    for (size_t oi = 0; oi < n; ++oi)
      {
        const size_t vi = order(oi);
        const Point &v = verts(vi);
        const Point dir = v;  // ray from query toward v
 
        // Nearest edge BEFORE processing events at this vertex.
        const size_t prev_near = status.min();
 
        // Remove ending edges.
        for (DynList<size_t>::Iterator it(ends(vi)); it.has_curr(); it.next_ne())
          status.erase(it.get_curr());
 
        // Insert starting edges.
        for (DynList<size_t>::Iterator it(starts(vi)); it.has_curr(); it.next_ne())
          status.insert(it.get_curr(), dir);
 
        // Nearest edge AFTER processing events.
        const size_t curr_near = status.min();
 
        // Determine visibility.
        bool v_is_on_edge = false;
        if (prev_near < n)
          {
            const size_t ea = prev_near, eb = (prev_near + 1) % n;
            if (vi == ea or vi == eb)
              v_is_on_edge = true;
          }
        if (curr_near < n and not v_is_on_edge)
          {
            const size_t ea = curr_near, eb = (curr_near + 1) % n;
            if (vi == ea or vi == eb)
              v_is_on_edge = true;
          }
 
        if (v_is_on_edge)
          {
            // Vertex is on the nearest edge — directly visible.
            vis_pts.append(v);
          }
        else if (prev_near != curr_near)
          {
            // Nearest edge changed — add intersection with old and new.
            if (prev_near < n)
              vis_pts.append(ray_edge_hit(query, dir, verts(prev_near), verts((prev_near + 1) % n)));
            vis_pts.append(v);
            if (curr_near < n)
              vis_pts.append(ray_edge_hit(query, dir, verts(curr_near), verts((curr_near + 1) % n)));
          }
      }
 
    // Remove duplicate consecutive points.
    Polygon result;
    for (size_t i = 0; i < vis_pts.size(); ++i)
      {
        if (i > 0 and vis_pts(i) == vis_pts(i - 1))
          continue;
        result.add_vertex(vis_pts(i));
      }
    if (result.size() >= 3)
      {
        // Remove last if the same as first.
        Array<Point> rv;
        for (Polygon::Vertex_Iterator it(result); it.has_curr(); it.next_ne())
          rv.append(it.get_current_vertex());
        if (rv.size() >= 2 and rv(0) == rv(rv.size() - 1))
          {
            Polygon cleaned;
            for (size_t i = 0; i + 1 < rv.size(); ++i)
              cleaned.add_vertex(rv(i));
            if (cleaned.size() >= 3)
              cleaned.close();
            return cleaned;
          }
        result.close();
      }
    return result;
  }
};
 
// ============================================================================
// Shortest Path in Simple Polygon (Lee-Preparata Funnel)
// ============================================================================
 
class ShortestPathInPolygon
{
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  struct ITri
  {
    size_t v[3];
    size_t adj[3];  // adj[i] = neighbour sharing edge opposite v[i], or NONE
  };
 
  [[nodiscard]] static size_t find_index(const Array<Point> &pts, const Point &p)
  {
    for (size_t i = 0; i < pts.size(); ++i)
      if (pts(i) == p)
        return i;
    return NONE;
  }
 
  [[nodiscard]] static Array<ITri> build_tris(const Array<Point> &pts, const DynList<Triangle> &tl)
  {
    // Convert to indexed form.
    Array<ITri> tris;
    for (DynList<Triangle>::Iterator it(tl); it.has_curr(); it.next_ne())
      {
        const Triangle &t = it.get_curr();
        ITri ti{};
        ti.v[0] = find_index(pts, t.get_p1());
        ti.v[1] = find_index(pts, t.get_p2());
        ti.v[2] = find_index(pts, t.get_p3());
        ti.adj[0] = ti.adj[1] = ti.adj[2] = NONE;
        tris.append(ti);
      }
 
    // Build adjacency via an edge map.
    // Key: (min_idx, max_idx), Value: (triangle_index, local_edge_index)
    struct EdgeKey
    {
      size_t u, v;
    };
 
    struct CmpEdge
    {
      bool operator () (const EdgeKey &a, const EdgeKey &b) const
      {
        if (a.u != b.u)
          return a.u < b.u;
        return a.v < b.v;
      }
    };
 
    struct EdgeVal
    {
      size_t tri;
      size_t local;
    };
 
    DynSetTree<EdgeKey, Avl_Tree, CmpEdge> edge_set;
 
    // We need a separate map. Use parallel arrays since DynSetTree doesn't
    // store mapped values.  Use a simpler approach: flat array scan.
    struct EdgeEntry
    {
      size_t u, v, tri, local;
    };
    Array<EdgeEntry> edges;
    edges.reserve(tris.size() * 3);
 
    for (size_t ti = 0; ti < tris.size(); ++ti)
      for (int e = 0; e < 3; ++e)
        {
          size_t u = tris(ti).v[(e + 1) % 3];
          size_t v = tris(ti).v[(e + 2) % 3];
          if (u > v)
            {
              const size_t tmp = u;
              u = v;
              v = tmp;
            }
          edges.append(EdgeEntry{u, v, ti, size_t(e)});
        }
 
    // Sort edges and find matching pairs.
    quicksort_op(edges, [](const EdgeEntry &a, const EdgeEntry &b)
      {
        if (a.u != b.u)
          return a.u < b.u;
        if (a.v != b.v)
          return a.v < b.v;
        return a.tri < b.tri;
      });
 
    for (size_t i = 0; i + 1 < edges.size(); ++i)
      if (edges(i).u == edges(i + 1).u and edges(i).v == edges(i + 1).v)
        {
          const size_t t1 = edges(i).tri, l1 = edges(i).local;
          const size_t t2 = edges(i + 1).tri, l2 = edges(i + 1).local;
          tris(t1).adj[l1] = t2;
          tris(t2).adj[l2] = t1;
          ++i;  // skip the matched pair
        }
 
    return tris;
  }
 
  [[nodiscard]] static bool point_in_triangle(const Array<Point> &pts, const ITri &t, const Point &p)
  {
    const Orientation o0 = orientation(pts(t.v[0]), pts(t.v[1]), p);
    const Orientation o1 = orientation(pts(t.v[1]), pts(t.v[2]), p);
    const Orientation o2 = orientation(pts(t.v[2]), pts(t.v[0]), p);
    const bool has_cw = o0 == Orientation::CW or o1 == Orientation::CW or o2 == Orientation::CW;
    const bool has_ccw = o0 == Orientation::CCW or o1 == Orientation::CCW or o2 == Orientation::CCW;
    return not (has_cw and has_ccw);
  }
 
  [[nodiscard]] static size_t find_tri(const Array<Point> &pts, const Array<ITri> &tris, const Point &p)
  {
    for (size_t i = 0; i < tris.size(); ++i)
      if (point_in_triangle(pts, tris(i), p))
        return i;
    return NONE;
  }
 
  [[nodiscard]] static Array<size_t> find_sleeve(const Array<ITri> &tris,
                                                 const size_t src,
                                                 const size_t dst)
  {
    if (src == dst)
      {
        Array<size_t> s;
        s.append(src);
        return s;
      }
 
    Array<size_t> parent;
    parent.reserve(tris.size());
    for (size_t i = 0; i < tris.size(); ++i)
      parent.append(NONE);
    parent(src) = src;  // sentinel
 
    DynList<size_t> queue;
    queue.append(src);
 
    while (not queue.is_empty())
      {
        const size_t cur = queue.remove_first();
        if (cur == dst)
          break;
        for (unsigned long nb : tris(cur).adj)
          if (nb != NONE and parent(nb) == NONE)
            {
              parent(nb) = cur;
              queue.append(nb);
            }
      }
 
    // Reconstruct path.
    Array<size_t> path;
    for (size_t cur = dst; cur != src; cur = parent(cur))
      path.append(cur);
    path.append(src);
 
    // Reverse.
    for (size_t i = 0; i < path.size() / 2; ++i)
      {
        const size_t tmp = path(i);
        path(i) = path(path.size() - 1 - i);
        path(path.size() - 1 - i) = tmp;
      }
    return path;
  }
 
  [[nodiscard]] static Geom_Number cross(const Point &a, const Point &b, const Point &c)
  {
    return (b.get_x() - a.get_x()) * (c.get_y() - a.get_y()) -
      (b.get_y() - a.get_y()) * (c.get_x() - a.get_x());
  }
 
public:
  [[nodiscard]] DynList<Point> operator () (const Polygon &polygon,
                                            const Point &source,
                                            const Point &target) const
  {
    ah_domain_error_if(not polygon.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(polygon.size() < 3) << "Polygon must have >= 3 vertices";
    ah_domain_error_if(not PointInPolygonWinding::contains(polygon, source))
      << "Source must be inside the polygon";
    ah_domain_error_if(not PointInPolygonWinding::contains(polygon, target))
      << "Target must be inside the polygon";
 
    DynList<Point> result;
    if (source == target)
      {
        result.append(source);
        return result;
      }
 
    // Check direct line of sight.
    {
      const Segment seg(source, target);
      bool blocked = false;
      for (Polygon::Segment_Iterator it(polygon); it.has_curr() and not blocked; it.next_ne())
        if (const Segment edge = it.get_current_segment(); seg.intersects_properly_with(edge))
          blocked = true;
      if (not blocked)
        {
          result.append(source);
          result.append(target);
          return result;
        }
    }
 
    // Extract vertices.
    Array<Point> pts;
    for (Polygon::Vertex_Iterator it(polygon); it.has_curr(); it.next_ne())
      pts.append(it.get_current_vertex());
 
    // Triangulate.
    CuttingEarsTriangulation triangulator;
    DynList<Triangle> tri_list = triangulator(polygon);
 
    ah_domain_error_if(tri_list.is_empty()) << "Triangulation failed";
 
    // Build indexed triangulation with adjacency.
    Array<ITri> tris = build_tris(pts, tri_list);
 
    // Locate source and target triangles.
    const size_t src_t = find_tri(pts, tris, source);
    const size_t dst_t = find_tri(pts, tris, target);
 
    ah_domain_error_if(src_t == NONE) << "Could not locate source in triangulation";
    ah_domain_error_if(dst_t == NONE) << "Could not locate target in triangulation";
 
    // Find sleeve.
    Array<size_t> sleeve = find_sleeve(tris, src_t, dst_t);
 
    if (sleeve.size() <= 1)
      {
        result.append(source);
        result.append(target);
        return result;
      }
 
    // ----------------------------------------------------------------
    // Simple Stupid Funnel Algorithm  (Mononen / Lee-Preparata).
    //
    // Build a portal list from the sleeve diagonals, then walk it
    // maintaining a funnel (apex, left boundary, right boundary).
    // ----------------------------------------------------------------
 
    // A portal is a pair (left, right) as seen when walking from source
    // toward target.  Portal 0 = (source, source), last = (target, target).
    struct Portal
    {
      Point left;
      Point right;
    };
    Array<Portal> portals;
    portals.append(Portal{source, source});
 
    // For each sleeve diagonal, find shared vertices and the "opposite"
    // vertex in the current triangle (the one NOT shared with the next).
    // Orient the portal using cross(V_prev, s0, s1):
    //   cross < 0  →  left = s0, right = s1
    //   cross > 0  →  left = s1, right = s0
    // This is robust regardless of triangulation order.
 
    for (size_t i = 0; i + 1 < sleeve.size(); ++i)
      {
        size_t s0 = 0, s1 = 0;
        size_t v_prev = 0;
        {
          int sc = 0;
          bool found[3] = {false, false, false};
          for (int a = 0; a < 3; ++a)
            for (unsigned long b : tris(sleeve(i + 1)).v)
              if (tris(sleeve(i)).v[a] == b)
                {
                  found[a] = true;
                  break;
                }
 
          for (int a = 0; a < 3; ++a)
            {
              if (found[a])
                {
                  if (sc == 0)
                    s0 = tris(sleeve(i)).v[a];
                  else
                    s1 = tris(sleeve(i)).v[a];
                  ++sc;
                }
              else
                v_prev = tris(sleeve(i)).v[a];
            }
        }
 
        const Geom_Number c = cross(pts(v_prev), pts(s0), pts(s1));
        if (c < 0)
          portals.append(Portal{pts(s0), pts(s1)});
        else
          portals.append(Portal{pts(s1), pts(s0)});
      }
 
    portals.append(Portal{target, target});
 
    // --- SSFA core ---
    Point apex = source;
    Point fl = source;  // funnel left boundary
    Point fr = source;  // funnel right boundary
    size_t ai = 0, li = 0, ri = 0;
 
    result.append(source);
 
    for (size_t i = 1; i < portals.size(); ++i)
      {
        const Point &pr = portals(i).right;
        const Point &pl = portals(i).left;
 
        // --- tighten right boundary ---
        if (cross(apex, fr, pr) >= 0)
          {
            if (apex == fr or cross(apex, fl, pr) < 0)
              {
                fr = pr;
                ri = i;
              }
            else
              {
                // Right crossed over left → left becomes new apex.
                result.append(fl);
                apex = fl;
                ai = li;
                fl = apex;
                fr = apex;
                li = ai;
                ri = ai;
                i = ai;  // loop increments to ai+1
                continue;
              }
          }
 
        // --- tighten left boundary ---
        if (cross(apex, fl, pl) <= 0)
          {
            if (apex == fl or cross(apex, fr, pl) > 0)
              {
                fl = pl;
                li = i;
              }
            else
              {
                // Left crossed over right → right becomes new apex.
                result.append(fr);
                apex = fr;
                ai = ri;
                fl = apex;
                fr = apex;
                li = ai;
                ri = ai;
                i = ai;
                continue;
              }
          }
      }
 
    if (result.get_last() != target)
      result.append(target);
    return result;
  }
};
 
// ============================================================================
// Segment Arrangement — Full Planar Subdivision
// ============================================================================
 
class SegmentArrangement
{
public:
  struct ArrEdge
  {
    size_t src;      
    size_t tgt;      
    size_t seg_idx;  
  };
 
  struct ArrFace
  {
    DynList<size_t> boundary;  
    bool unbounded;            
  };
 
  struct Result
  {
    Array<Point> vertices;  
    Array<ArrEdge> edges;   
    Array<ArrFace> faces;   
  };
 
private:
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  [[nodiscard]] static bool pt_less(const Point &a, const Point &b)
  {
    if (a.get_x() != b.get_x())
      return a.get_x() < b.get_x();
    return a.get_y() < b.get_y();
  }
 
  [[nodiscard]] static size_t find_vertex(const Array<Point> &verts, const Point &p)
  {
    size_t lo = 0, hi = verts.size();
    while (lo < hi)
      if (const size_t mid = lo + (hi - lo) / 2; pt_less(verts(mid), p))
        lo = mid + 1;
      else if (pt_less(p, verts(mid)))
        hi = mid;
      else
        return mid;
    return NONE;
  }
 
  [[nodiscard]] static int angle_quad(const Geom_Number &dx, const Geom_Number &dy)
  {
    if (dx > 0 and dy >= 0)
      return 0;
    if (dx <= 0 and dy > 0)
      return 1;
    if (dx < 0 and dy <= 0)
      return 2;
    return 3;
  }
 
  [[nodiscard]] static bool angle_lt(const Geom_Number &dx1,
                                     const Geom_Number &dy1,
                                     const Geom_Number &dx2,
                                     const Geom_Number &dy2)
  {
    const int q1 = angle_quad(dx1, dy1);
    const int q2 = angle_quad(dx2, dy2);
    if (q1 != q2)
      return q1 < q2;
    if (const Geom_Number cross = dx1 * dy2 - dy1 * dx2; cross != 0)
      return cross > 0;
    return dx1 * dx1 + dy1 * dy1 < (dx2 * dx2 + dy2 * dy2);
  }
 
  struct HalfEdge
  {
    size_t origin;    
    size_t target;    
    size_t twin;      
    size_t next;      
    size_t face;      
    size_t edge_idx;  
  };
 
public:
  [[nodiscard]] Result operator () (const Array<Segment> &segments) const
  {
    Result ret;
    const size_t n = segments.size();
 
    if (n == 0)
      {
        // Single unbounded face.
        ArrFace uf;
        uf.unbounded = true;
        ret.faces.append(uf);
        return ret;
      }
 
    // --- Step 1: Compute all intersections. ---
    SweepLineSegmentIntersection sweep;
    auto inters = sweep(segments);
 
    // --- Step 2: Build a deduplicated vertex set. ---
    // Collect all endpoints + intersection points.
    Array<Point> all_pts;
    all_pts.reserve(2 * n + inters.size());
    for (size_t i = 0; i < n; ++i)
      {
        all_pts.append(segments(i).get_src_point());
        all_pts.append(segments(i).get_tgt_point());
      }
    for (size_t i = 0; i < inters.size(); ++i)
      all_pts.append(inters(i).point);
 
    // Sort lexicographically.
    quicksort_op(all_pts, [](const Point &a, const Point &b)
      {
        return pt_less(a, b);
      });
 
    // Deduplicate.
    ret.vertices.reserve(all_pts.size());
    for (size_t i = 0; i < all_pts.size(); ++i)
      if (ret.vertices.is_empty() or ret.vertices.get_last() != all_pts(i))
        ret.vertices.append(all_pts(i));
 
    // --- Step 3: Split segments into sub-edges. ---
    // For each segment, collect its vertices and sort along the segment.
    for (size_t si = 0; si < n; ++si)
      {
        const Point &sp = segments(si).get_src_point();
        const Point &tp = segments(si).get_tgt_point();
 
        // Collect vertices on this segment.
        Array<size_t> on_seg;
        on_seg.append(find_vertex(ret.vertices, sp));
        on_seg.append(find_vertex(ret.vertices, tp));
 
        // Add intersection points involving this segment.
        for (size_t ki = 0; ki < inters.size(); ++ki)
          if (inters(ki).seg_i == si or inters(ki).seg_j == si)
            if (const size_t vi = find_vertex(ret.vertices, inters(ki).point); vi != NONE)
              on_seg.append(vi);
 
        // Deduplicate.
        quicksort_op(on_seg, [](const size_t a, const size_t b)
          {
            return a < b;
          });
        {
          Array<size_t> uniq;
          for (size_t i = 0; i < on_seg.size(); ++i)
            if (uniq.is_empty() or uniq.get_last() != on_seg(i))
              uniq.append(on_seg(i));
          on_seg = uniq;
        }
 
        // Sort by parametric position along the segment.
        // Use the primary direction (x for non-vertical, y for vertical).
        const bool vertical = (sp.get_x() == tp.get_x());
        const auto &verts = ret.vertices;
        if (vertical)
          quicksort_op(on_seg, [&](const size_t a, const size_t b)
            {
              return verts(a).get_y() < verts(b).get_y();
            });
        else
          quicksort_op(on_seg, [&](const size_t a, const size_t b)
            {
              return verts(a).get_x() < verts(b).get_x();
            });
 
        // Create edges between consecutive vertices.
        for (size_t i = 0; i + 1 < on_seg.size(); ++i)
          ret.edges.append(ArrEdge{on_seg(i), on_seg(i + 1), si});
      }
 
    // --- Step 4 + 5: Build half-edges, compute next pointers, find faces. ---
    const size_t ne = ret.edges.size();
    const size_t nhe = 2 * ne;
    const size_t nv = ret.vertices.size();
 
    if (ne == 0)
      {
        // Only isolated vertices, no edges → one unbounded face.
        ArrFace uf;
        uf.unbounded = true;
        ret.faces.append(uf);
        return ret;
      }
 
    // Create half-edges: for edge i, half-edge 2*i goes src→tgt,
    //                                  half-edge 2*i+1 goes tgt→src.
    Array<HalfEdge> he;
    he.reserve(nhe);
    for (size_t i = 0; i < ne; ++i)
      {
        he.append(HalfEdge{ret.edges(i).src, ret.edges(i).tgt, 2 * i + 1, NONE, NONE, i});
        he.append(HalfEdge{ret.edges(i).tgt, ret.edges(i).src, 2 * i, NONE, NONE, i});
      }
 
    // Build incidence: for each vertex, list of outgoing half-edge indices.
    Array<Array<size_t>> inc;
    inc.reserve(nv);
    for (size_t i = 0; i < nv; ++i)
      inc.append(Array<size_t>());
    for (size_t h = 0; h < nhe; ++h)
      inc(he(h).origin).append(h);
 
    // Sort outgoing half-edges at each vertex by angle.
    const auto &verts = ret.vertices;
    for (size_t v = 0; v < nv; ++v)
      {
        if (inc(v).size() <= 1)
          continue;
        quicksort_op(inc(v), [&](size_t a, size_t b)
          {
            const Geom_Number dxa = verts(he(a).target).get_x() - verts(v).get_x();
            const Geom_Number dya = verts(he(a).target).get_y() - verts(v).get_y();
            const Geom_Number dxb = verts(he(b).target).get_x() - verts(v).get_x();
            const Geom_Number dyb = verts(he(b).target).get_y() - verts(v).get_y();
            return angle_lt(dxa, dya, dxb, dyb);
          });
      }
 
    // Compute "next" pointers.
    // For half-edge h = (u→v), the next half-edge around the face is:
    // at vertex v, take the twin of h (which is v→u), find its position
    // in the sorted incidence list of v, go one step CW (previous in CCW
    // order) → that's the next half-edge of the face.
    //
    // Equivalently: next(h) where h = u→v:
    //   twin(h) = v→u.  Find twin(h) in inc(v).  The previous entry in
    //   inc(v) (wrapping) is the next half-edge of the face.
    for (size_t v = 0; v < nv; ++v)
      {
        const auto &list = inc(v);
        const size_t sz = list.size();
        if (sz == 0)
          continue;
 
        for (size_t i = 0; i < sz; ++i)
          {
            // Half-edge list(i) leaves v.  Its twin arrives at v.
            // The twin is the "incoming" half-edge.  The face's "next"
            // after the twin is the one that comes just before list(i)
            // in the CCW angular order, i.e. the one CW from it.
            // So: next(twin(list(i))) = list((i+1) % sz)
            //   wrong — let me re-derive.
            //
            // We have inc(v) sorted CCW: h0, h1, ..., h_{k-1} (outgoing).
            // For outgoing h_i (= v → t_i), twin(h_i) = t_i → v (incoming).
            // The face containing twin(h_i) continues with the next outgoing
            // half-edge at v going CW from the incoming direction.
            //
            // Incoming direction of twin(h_i) at v: from t_i toward v.
            // This is the reverse of h_i's outgoing direction.
            // In the CCW list, h_i is at position i.  The CW-next after
            // the reversed direction of h_i corresponds to h_{(i-1+k)%k}.
            //
            // So: next(twin(h_i)) = h_{(i-1+k) % k}.
 
            const size_t prev = (i == 0) ? sz - 1 : i - 1;
            he(he(list(i)).twin).next = list(prev);
          }
      }
 
    // --- Face traversal ---
    Array<bool> visited;
    visited.reserve(nhe);
    for (size_t i = 0; i < nhe; ++i)
      visited.append(false);
 
    for (size_t h = 0; h < nhe; ++h)
      {
        if (visited(h))
          continue;
 
        ArrFace face;
        face.unbounded = false;
 
        // Trace the face boundary.
        size_t cur = h;
        Geom_Number signed_area = 0;
        do
          {
            visited(cur) = true;
            face.boundary.append(he(cur).origin);
 
            // Accumulate signed area (shoelace).
            const Point &p1 = verts(he(cur).origin);
            const Point &p2 = verts(he(cur).target);
            signed_area += p1.get_x() * p2.get_y() - p2.get_x() * p1.get_y();
 
            cur = he(cur).next;
        } while (cur != h and cur != NONE);
 
        // CW winding (negative area) → unbounded face.
        if (signed_area < 0)
          face.unbounded = true;
 
        ret.faces.append(face);
      }
 
    // Ensure exactly one unbounded face is marked.
    // If none was found (e.g. all half-edges form CCW cycles, which
    // happens when all segments are isolated non-intersecting ones),
    // mark the face with the largest absolute signed area as unbounded.
    {
      bool has_ub = false;
      for (size_t i = 0; i < ret.faces.size(); ++i)
        if (ret.faces(i).unbounded)
          {
            has_ub = true;
            break;
          }
      if (not has_ub and not ret.faces.is_empty())
        ret.faces(0).unbounded = true;
    }
 
    return ret;
  }
};
 
// ============================================================================
// Alpha Shapes — Generalization of Convex Hull
// ============================================================================
 
class AlphaShape
{
public:
  struct Result
  {
    Array<Point> sites;  
    Array<DelaunayTriangulationBowyerWatson::IndexedTriangle>
      triangles;                    
    Array<Segment> boundary_edges;  
  };
 
  [[nodiscard]] Result operator () (const DynList<Point> &points, const Geom_Number &alpha_squared) const
  {
    constexpr DelaunayTriangulationBowyerWatson delaunay;
    auto [sites, triangles] = delaunay(points);
 
    Result ret;
    ret.sites = sites;
 
    if (triangles.size() == 0)
      return ret;
 
    // Filter triangles by circumradius².
    Array<bool> kept;
    kept.reserve(triangles.size());
    for (size_t t = 0; t < triangles.size(); ++t)
      {
        const auto &tri = triangles(t);
        const Point &a = sites(tri.i);
        const Point &b = sites(tri.j);
        const Point &c = sites(tri.k);
 
        // Circumradius² = (|AB|²|BC|²|CA|²) / (16 * area²)
        const Geom_Number ab2 = a.distance_squared_to(b);
        const Geom_Number bc2 = b.distance_squared_to(c);
        const Geom_Number ca2 = c.distance_squared_to(a);
        const Geom_Number area2x = area_of_parallelogram(a, b, c);
        const Geom_Number four_area_sq = area2x * area2x;
 
        // circumradius² = ab2 * bc2 * ca2 / (4 * four_area_sq)
        // Compare: ab2 * bc2 * ca2 ≤ alpha_squared * 4 * four_area_sq
        const bool pass = ab2 * bc2 * ca2 <= alpha_squared * four_area_sq * 4;
        kept.append(pass);
        if (pass)
          ret.triangles.append(tri);
      }
 
    // Extract boundary edges: edges appearing in exactly one kept triangle.
    // Use a simple count map via sorted edge keys.
    struct EdgeKey
    {
      size_t u, v;  
 
      bool operator == (const EdgeKey &o) const
      {
        return u == o.u and v == o.v;
      }
 
      bool operator < (const EdgeKey &o) const
      {
        return u < o.u or (u == o.u and v < o.v);
      }
    };
 
    auto make_key = [](const size_t a, const size_t b) -> EdgeKey
      {
        return a < b ? EdgeKey{a, b} : EdgeKey{b, a};
      };
 
    Array<EdgeKey> all_edges;
    all_edges.reserve(ret.triangles.size() * 3);
    for (size_t t = 0; t < ret.triangles.size(); ++t)
      {
        const auto &[i, j, k] = ret.triangles(t);
        all_edges.append(make_key(i, j));
        all_edges.append(make_key(j, k));
        all_edges.append(make_key(k, i));
      }
 
    quicksort_op(all_edges, [](const EdgeKey &a, const EdgeKey &b)
      {
        return a < b;
      });
 
    for (size_t i = 0; i < all_edges.size();)
      {
        size_t j = i + 1;
        while (j < all_edges.size() and all_edges(j) == all_edges(i))
          ++j;
        if (j - i == 1)  // appears exactly once → boundary
          ret.boundary_edges.append(Segment(ret.sites(all_edges(i).u), ret.sites(all_edges(i).v)));
        i = j;
      }
 
    return ret;
  }
};
 
// ============================================================================
// Power Diagram — Weighted Voronoi
// ============================================================================
 
class PowerDiagram
{
public:
  struct WeightedSite
  {
    Point position;      
    Geom_Number weight;  
  };
 
  struct PowerEdge
  {
    size_t site_u;    
    size_t site_v;    
    Point src;        
    Point tgt;        
    bool unbounded;   
    Point direction;  
  };
 
  struct PowerCell
  {
    size_t site_index;      
    Point site;             
    Geom_Number weight;     
    bool bounded;           
    Array<Point> vertices;  
  };
 
  struct Result
  {
    Array<WeightedSite> sites;  
    Array<Point> vertices;      
    Array<PowerEdge> edges;     
    Array<PowerCell> cells;     
  };
 
  [[nodiscard]] static Point power_center(const WeightedSite &a,
                                          const WeightedSite &b,
                                          const WeightedSite &c)
  {
    // Power center solves:
    //   ||p - a||² - wa = ||p - b||² - wb = ||p - c||² - wc
    // Expanding:  2(bx-ax)px + 2(by-ay)py = bx²+by²-ax²-ay² - (wb - wa)
    //             2(cx-ax)px + 2(cy-ay)py = cx²+cy²-ax²-ay² - (wc - wa)
    const Geom_Number &ax = a.position.get_x();
    const Geom_Number &ay = a.position.get_y();
    const Geom_Number &bx = b.position.get_x();
    const Geom_Number &by = b.position.get_y();
    const Geom_Number &cx = c.position.get_x();
    const Geom_Number &cy = c.position.get_y();
 
    const Geom_Number d1x = bx - ax, d1y = by - ay;
    const Geom_Number d2x = cx - ax, d2y = cy - ay;
 
    const Geom_Number rhs1 = (bx * bx + by * by - ax * ax - ay * ay - (b.weight - a.weight)) / 2;
    const Geom_Number rhs2 = (cx * cx + cy * cy - ax * ax - ay * ay - (c.weight - a.weight)) / 2;
 
    const Geom_Number det = d1x * d2y - d1y * d2x;
    ah_domain_error_if(det == 0) << "Degenerate configuration";
 
    return {(rhs1 * d2y - rhs2 * d1y) / det, (d1x * rhs2 - d2x * rhs1) / det};
  }
 
  [[nodiscard]] Result operator () (const Array<WeightedSite> &sites) const
  {
    Result ret;
    const size_t n = sites.size();
    if (n == 0)
      return ret;
 
    ret.sites = sites;
 
    // Compute regular triangulation (weighted Delaunay).
    Array<RegularTriangulationBowyerWatson::WeightedSite> rt_input;
    rt_input.reserve(n);
    for (size_t i = 0; i < n; ++i)
      rt_input.append({sites(i).position, sites(i).weight});
 
    constexpr RegularTriangulationBowyerWatson reg_tri;
    auto rt = reg_tri(rt_input);
 
    if (rt.triangles.size() == 0)
      return ret;
 
    // Build a mapping from regular-triangulation site indices to ours.
    // rt.sites may have been reordered/deduped, so match by position.
    Array<size_t> rt_to_ours;
    rt_to_ours.reserve(rt.sites.size());
    for (size_t ri = 0; ri < rt.sites.size(); ++ri)
      {
        size_t match = 0;
        for (size_t oi = 0; oi < n; ++oi)
          if (rt.sites(ri).position == sites(oi).position)
            {
              match = oi;
              break;
            }
        rt_to_ours.append(match);
      }
 
    // Compute power centers for each regular triangle.
    Array<Point> pcenters;
    pcenters.reserve(rt.triangles.size());
    for (size_t t = 0; t < rt.triangles.size(); ++t)
      {
        const auto &tri = rt.triangles(t);
        pcenters.append(power_center(sites(rt_to_ours(tri.i)), sites(rt_to_ours(tri.j)),
                                     sites(rt_to_ours(tri.k))));
      }
 
    ret.vertices = pcenters;
 
    // Identify hull sites: sites on boundary edges (edges shared by
    // exactly one triangle) have unbounded power cells.
    DynSetTree<size_t, Treap_Rk> hull_sites;
 
    GeomTriangleAdjacencyUtils::for_each_sorted_edge_group(
      rt.triangles,
      [&](const Array<GeomTriangleAdjacencyUtils::EdgeRef> &edge_refs, const size_t first,
          const size_t last)
      {
        if (last - first == 1)
          {
            // Boundary edge: both sites are on the convex hull.
            hull_sites.insert(rt_to_ours(edge_refs(first).u));
            hull_sites.insert(rt_to_ours(edge_refs(first).v));
          }
 
        // In a manifold triangulation this group has exactly 1 or 2 refs.
        // If degeneracies produce >2, connect all pairs defensively.
        if (last - first >= 2)
          for (size_t a = first; a + 1 < last; ++a)
            for (size_t b = a + 1; b < last; ++b)
              {
                PowerEdge pe;
                pe.site_u = rt_to_ours(edge_refs(first).u);
                pe.site_v = rt_to_ours(edge_refs(first).v);
                pe.src = pcenters(edge_refs(a).tri);
                pe.tgt = pcenters(edge_refs(b).tri);
                pe.unbounded = false;
                pe.direction = Point(0, 0);
                ret.edges.append(pe);
              }
      });
 
    // Build cells: hull sites have unbounded cells.
    ret.cells.reserve(n);
    for (size_t s = 0; s < n; ++s)
      {
        PowerCell cell;
        cell.site_index = s;
        cell.site = sites(s).position;
        cell.weight = sites(s).weight;
        cell.bounded = hull_sites.search(s) == nullptr;
 
        // Collect power centers of triangles incident to this site.
        for (size_t t = 0; t < rt.triangles.size(); ++t)
          {
            const auto &[i, j, k] = rt.triangles(t);
            if (rt_to_ours(i) == s or rt_to_ours(j) == s or rt_to_ours(k) == s)
              cell.vertices.append(pcenters(t));
          }
 
        ret.cells.append(cell);
      }
 
    return ret;
  }
};
 
// ============================================================================
// Bezier Curves
// ============================================================================
 
class BezierCurve
{
public:
  [[nodiscard]] static Point quadratic(const Point &p0,
                                       const Point &p1,
                                       const Point &p2,
                                       const Geom_Number &t)
  {
    const Geom_Number s = Geom_Number(1) - t;
    const Geom_Number s2 = s * s;
    const Geom_Number t2 = t * t;
    const Geom_Number st2 = Geom_Number(2) * s * t;
 
    return {s2 * p0.get_x() + st2 * p1.get_x() + t2 * p2.get_x(),
            s2 * p0.get_y() + st2 * p1.get_y() + t2 * p2.get_y()};
  }
 
  [[nodiscard]] static Point cubic(const Point &p0,
                                   const Point &p1,
                                   const Point &p2,
                                   const Point &p3,
                                   const Geom_Number &t)
  {
    const Geom_Number s = Geom_Number(1) - t;
    const Geom_Number s2 = s * s;
    const Geom_Number s3 = s2 * s;
    const Geom_Number t2 = t * t;
    const Geom_Number t3 = t2 * t;
    const Geom_Number c1 = Geom_Number(3) * s2 * t;
    const Geom_Number c2 = Geom_Number(3) * s * t2;
 
    return {s3 * p0.get_x() + c1 * p1.get_x() + c2 * p2.get_x() + t3 * p3.get_x(),
            s3 * p0.get_y() + c1 * p1.get_y() + c2 * p2.get_y() + t3 * p3.get_y()};
  }
 
  [[nodiscard]] static Array<Point> sample_quadratic(const Point &p0,
                                                     const Point &p1,
                                                     const Point &p2,
                                                     const size_t n)
  {
    ah_domain_error_if(n == 0) << "Need at least 1 subdivision";
    Array<Point> pts;
    pts.reserve(n + 1);
    for (size_t i = 0; i <= n; ++i)
      pts.append(quadratic(p0, p1, p2,
                           Geom_Number(static_cast<long>(i)) / Geom_Number(static_cast<long>(n))));
    return pts;
  }
 
  [[nodiscard]] static Array<Point> sample_cubic(const Point &p0,
                                                 const Point &p1,
                                                 const Point &p2,
                                                 const Point &p3,
                                                 const size_t n)
  {
    ah_domain_error_if(n == 0) << "Need at least 1 subdivision";
    Array<Point> pts;
    pts.reserve(n + 1);
    for (size_t i = 0; i <= n; ++i)
      pts.append(cubic(p0, p1, p2, p3,
                       Geom_Number(static_cast<long>(i)) / Geom_Number(static_cast<long>(n))));
    return pts;
  }
 
  struct SplitResult
  {
    Point left[4];
    Point right[4];
  };
 
  [[nodiscard]] static SplitResult split_cubic(const Point &p0,
                                               const Point &p1,
                                               const Point &p2,
                                               const Point &p3,
                                               const Geom_Number &t)
  {
    auto lerp = [&](const Point &a, const Point &b) -> Point
      {
        const Geom_Number s = Geom_Number(1) - t;
        return {s * a.get_x() + t * b.get_x(), s * a.get_y() + t * b.get_y()};
      };
 
    const Point q0 = lerp(p0, p1);
    const Point q1 = lerp(p1, p2);
    const Point q2 = lerp(p2, p3);
    const Point r0 = lerp(q0, q1);
    const Point r1 = lerp(q1, q2);
    const Point s0 = lerp(r0, r1);
 
    SplitResult sr;
    sr.left[0] = p0;
    sr.left[1] = q0;
    sr.left[2] = r0;
    sr.left[3] = s0;
    sr.right[0] = s0;
    sr.right[1] = r1;
    sr.right[2] = q2;
    sr.right[3] = p3;
    return sr;
  }
 
  [[nodiscard]] static Rectangle control_bbox(const Point &p0,
                                              const Point &p1,
                                              const Point &p2,
                                              const Point &p3)
  {
    Geom_Number mnx = p0.get_x(), mxx = p0.get_x();
    Geom_Number mny = p0.get_y(), mxy = p0.get_y();
    auto update = [&](const Point &p)
      {
        if (p.get_x() < mnx)
          mnx = p.get_x();
        if (p.get_x() > mxx)
          mxx = p.get_x();
        if (p.get_y() < mny)
          mny = p.get_y();
        if (p.get_y() > mxy)
          mxy = p.get_y();
      };
    update(p1);
    update(p2);
    update(p3);
    return {mnx, mny, mxx, mxy};
  }
 
  [[nodiscard]] static Polygon approximate_quadratic(const Point &p0,
                                                     const Point &p1,
                                                     const Point &p2,
                                                     const size_t n)
  {
    auto pts = sample_quadratic(p0, p1, p2, n);
    Polygon poly;
    for (size_t i = 0; i < pts.size(); ++i)
      poly.add_vertex(pts(i));
    return poly;
  }
 
  [[nodiscard]] static Polygon approximate_cubic(const Point &p0,
                                                 const Point &p1,
                                                 const Point &p2,
                                                 const Point &p3,
                                                 const size_t n)
  {
    auto pts = sample_cubic(p0, p1, p2, p3, n);
    Polygon poly;
    for (size_t i = 0; i < pts.size(); ++i)
      poly.add_vertex(pts(i));
    return poly;
  }
};
 
// ============================================================================
// Boolean Polygon Operations
// ============================================================================
 
class BooleanPolygonOperations
{
public:
  enum class Op
  {
    INTERSECTION,  
    UNION,         
    DIFFERENCE     
  };
 
  [[nodiscard]] Array<Polygon> operator () (const Polygon &a, const Polygon &b, Op op) const
  {
    ah_domain_error_if(not a.is_closed()) << "First polygon must be closed";
    ah_domain_error_if(not b.is_closed()) << "Second polygon must be closed";
    ah_domain_error_if(a.size() < 3) << "First polygon must have >= 3 vertices";
    ah_domain_error_if(b.size() < 3) << "Second polygon must have >= 3 vertices";
 
    switch (op)
      {
      case Op::INTERSECTION:
        return compute_intersection(a, b);
      case Op::UNION:
        return compute_union(a, b);
      case Op::DIFFERENCE:
        return compute_difference(a, b);
      }
    return {};
  }
 
  [[nodiscard]] Array<Polygon> intersection(const Polygon &a, const Polygon &b) const
  {
    return (*this)(a, b, Op::INTERSECTION);
  }
 
  [[nodiscard]] Array<Polygon> polygon_union(const Polygon &a, const Polygon &b) const
  {
    return (*this)(a, b, Op::UNION);
  }
 
  [[nodiscard]] Array<Polygon> difference(const Polygon &a, const Polygon &b) const
  {
    return (*this)(a, b, Op::DIFFERENCE);
  }
 
private:
  // ----- Greiner-Hormann node for augmented polygon vertex list -----
 
  struct GHNode
  {
    Point pt;
    bool intersect = false;
    bool entering = false;
    size_t neighbor = SIZE_MAX;  // index in the other polygon's list
    bool visited = false;
    Geom_Number alpha = 0;  // parameter along the original edge
  };
 
  // ----- helpers -----
 
  [[nodiscard]] static Array<Point> extract(const Polygon &p)
  {
    return GeomPolygonUtils::extract_vertices(p);
  }
 
  static void ensure_ccw(Array<Point> &v)
  {
    GeomPolygonUtils::ensure_ccw(v);
  }
 
  static void reverse_array(Array<Point> &v)
  {
    for (size_t i = 0, j = v.size() - 1; i < j; ++i, --j)
      {
        const Point tmp = v(i);
        v(i) = v(j);
        v(j) = tmp;
      }
  }
 
  [[nodiscard]] static Polygon build_poly(const Array<Point> &pts)
  {
    Polygon p;
    for (size_t i = 0; i < pts.size(); ++i)
      p.add_vertex(pts(i));
    if (pts.size() >= 3)
      p.close();
    return p;
  }
 
  [[nodiscard]] static Geom_Number edge_param(const Point &P, const Point &Q, const Point &I)
  {
    const Geom_Number dx = Q.get_x() - P.get_x();
    if (dx != 0)
      return (I.get_x() - P.get_x()) / dx;
    return (I.get_y() - P.get_y()) / (Q.get_y() - P.get_y());
  }
 
  [[nodiscard]] static bool point_inside_ccw(const Array<Point> &poly, const Point &p)
  {
    int winding = 0;
    const size_t n = poly.size();
    for (size_t i = 0; i < n; ++i)
      {
        const Point &a = poly(i);
        const Point &b = poly((i + 1) % n);
        const Segment edge(a, b);
        if (edge.contains(p))
          return true;
        if (a.get_y() <= p.get_y())
          {
            if (b.get_y() > p.get_y() && area_of_parallelogram(a, b, p) > 0)
              ++winding;
          }
        else
          {
            if (b.get_y() <= p.get_y() && area_of_parallelogram(a, b, p) < 0)
              --winding;
          }
      }
    return winding != 0;
  }
 
  static void sort_indices_by_alpha(Array<size_t> &idx, const Array<Geom_Number> &keys)
  {
    for (size_t i = 1; i < idx.size(); ++i)
      {
        const size_t val = idx(i);
        const Geom_Number &key = keys(val);
        size_t j = i;
        while (j > 0 && keys(idx(j - 1)) > key)
          {
            idx(j) = idx(j - 1);
            --j;
          }
        idx(j) = val;
      }
  }
 
  // ----- Core Greiner-Hormann algorithm -----
 
  struct IsectPair
  {
    Point pt;
    size_t edge_a, edge_b;
    Geom_Number alpha_a, alpha_b;
  };
 
  [[nodiscard]] static Array<Polygon> greiner_hormann(const Array<Point> &va,
                                                      const Array<Point> &vb,
                                                      bool start_entering)
  {
    const size_t na = va.size();
    const size_t nb = vb.size();
 
    // --- Phase 1: find all proper intersection pairs ---
 
    Array<IsectPair> pairs;
 
    for (size_t i = 0; i < na; ++i)
      {
        const Point &a0 = va(i);
        const Point &a1 = va((i + 1) % na);
        const Segment sa(a0, a1);
 
        for (size_t j = 0; j < nb; ++j)
          {
            const Point &b0 = vb(j);
            const Point &b1 = vb((j + 1) % nb);
            const Segment sb(b0, b1);
 
            if (not sa.intersects_properly_with(sb))
              continue;
 
            const Point ip = sa.intersection_with(sb);
            const Geom_Number aa = edge_param(a0, a1, ip);
            const Geom_Number ab = edge_param(b0, b1, ip);
            pairs.append({ip, i, j, aa, ab});
          }
      }
 
    // --- Phase 2: build augmented lists ---
 
    Array<GHNode> list_a, list_b;
    // pair_idx_a[k] / pair_idx_b[k] = position in list_a / list_b for
    // intersection pair k.
    Array<size_t> pair_idx_a, pair_idx_b;
    pair_idx_a.reserve(pairs.size());
    pair_idx_b.reserve(pairs.size());
    for (size_t k = 0; k < pairs.size(); ++k)
      {
        pair_idx_a.append(0);
        pair_idx_b.append(0);
      }
 
    // Build list_a: for each edge, add original vertex then sorted
    // intersections.
    for (size_t i = 0; i < na; ++i)
      {
        GHNode vn;
        vn.pt = va(i);
        list_a.append(vn);
 
        // Collect pairs on this edge of A.
        Array<size_t> edge_pairs;
        Array<Geom_Number> edge_alphas;
        for (size_t k = 0; k < pairs.size(); ++k)
          if (pairs(k).edge_a == i)
            {
              edge_pairs.append(k);
              edge_alphas.append(pairs(k).alpha_a);
            }
 
        // Sort by alpha.
        Array<size_t> order;
        for (size_t p = 0; p < edge_pairs.size(); ++p)
          order.append(p);
        sort_indices_by_alpha(order, edge_alphas);
 
        for (size_t p = 0; p < order.size(); ++p)
          {
            const size_t k = edge_pairs(order(p));
            pair_idx_a(k) = list_a.size();
            GHNode in;
            in.pt = pairs(k).pt;
            in.intersect = true;
            in.alpha = pairs(k).alpha_a;
            list_a.append(in);
          }
      }
 
    // Build list_b analogously.
    for (size_t j = 0; j < nb; ++j)
      {
        GHNode vn;
        vn.pt = vb(j);
        list_b.append(vn);
 
        Array<size_t> edge_pairs;
        Array<Geom_Number> edge_alphas;
        for (size_t k = 0; k < pairs.size(); ++k)
          if (pairs(k).edge_b == j)
            {
              edge_pairs.append(k);
              edge_alphas.append(pairs(k).alpha_b);
            }
 
        Array<size_t> order;
        for (size_t p = 0; p < edge_pairs.size(); ++p)
          order.append(p);
        sort_indices_by_alpha(order, edge_alphas);
 
        for (size_t p = 0; p < order.size(); ++p)
          {
            const size_t k = edge_pairs(order(p));
            pair_idx_b(k) = list_b.size();
            GHNode in;
            in.pt = pairs(k).pt;
            in.intersect = true;
            in.alpha = pairs(k).alpha_b;
            list_b.append(in);
          }
      }
 
    // Set neighbor links.
    for (size_t k = 0; k < pairs.size(); ++k)
      {
        list_a(pair_idx_a(k)).neighbor = pair_idx_b(k);
        list_b(pair_idx_b(k)).neighbor = pair_idx_a(k);
      }
 
    // --- Phase 3: mark entry / exit ---
 
    // Walk list_a; determine if the first original vertex of A is
    // inside B.
    {
      bool inside = point_inside_ccw(vb, va(0));
      for (size_t i = 0; i < list_a.size(); ++i)
        if (list_a(i).intersect)
          {
            list_a(i).entering = !inside;
            inside = !inside;
          }
    }
 
    // Walk list_b similarly w.r.t. A.
    {
      bool inside = point_inside_ccw(va, vb(0));
      for (size_t j = 0; j < list_b.size(); ++j)
        if (list_b(j).intersect)
          {
            list_b(j).entering = !inside;
            inside = !inside;
          }
    }
 
    // --- Phase 4: traverse ---
 
    Array<Polygon> result;
    const size_t safety_limit = list_a.size() + list_b.size() + pairs.size() * 2;
 
    for (size_t s = 0; s < list_a.size(); ++s)
      {
        if (not list_a(s).intersect)
          continue;
        if (list_a(s).visited)
          continue;
        if (list_a(s).entering != start_entering)
          continue;
 
        // Trace one result polygon.
        Array<Point> boundary;
        bool on_a = true;
        size_t idx = s;
        size_t steps = 0;
 
        do
          {
            auto &cur_list = on_a ? list_a : list_b;
 
            // Mark current intersection visited (and its partner).
            cur_list(idx).visited = true;
            if (cur_list(idx).neighbor != SIZE_MAX)
              {
                auto &other = on_a ? list_b : list_a;
                other(cur_list(idx).neighbor).visited = true;
              }
 
            // Record this intersection point.
            boundary.append(cur_list(idx).pt);
 
            // Walk forward until the next intersection node.
            idx = (idx + 1) % cur_list.size();
            while (not cur_list(idx).intersect)
              {
                boundary.append(cur_list(idx).pt);
                idx = (idx + 1) % cur_list.size();
                if (++steps > safety_limit)
                  goto done_poly;
              }
 
            // idx is now at the next intersection — mark it and switch.
            cur_list(idx).visited = true;
            {
              auto &other = on_a ? list_b : list_a;
              const size_t nbr = cur_list(idx).neighbor;
              other(nbr).visited = true;
              on_a = !on_a;
              idx = nbr;
            }
 
            if (++steps > safety_limit)
              break;
        } while (!(on_a && idx == s));
 
      done_poly:
        if (boundary.size() >= 3)
          result.append(build_poly(boundary));
      }
 
    return result;
  }
 
  // ----- Operation dispatchers -----
 
  static Array<Polygon> compute_intersection(const Polygon &a, const Polygon &b)
  {
    Array<Point> va = extract(a);
    Array<Point> vb = extract(b);
    ensure_ccw(va);
    ensure_ccw(vb);
 
    Array<Polygon> res = greiner_hormann(va, vb, /*start_entering=*/true);
 
    if (not res.is_empty())
      return res;
 
    // No proper intersections — check containment.
    if (point_inside_ccw(vb, va(0)))
      {
        // A entirely inside B → intersection is A.
        res.append(a);
        return res;
      }
    if (point_inside_ccw(va, vb(0)))
      {
        // B entirely inside A → intersection is B.
        res.append(b);
        return res;
      }
    // Disjoint.
    return res;
  }
 
  static Array<Polygon> compute_union(const Polygon &a, const Polygon &b)
  {
    Array<Point> va = extract(a);
    Array<Point> vb = extract(b);
    ensure_ccw(va);
    ensure_ccw(vb);
 
    Array<Polygon> res = greiner_hormann(va, vb, /*start_entering=*/false);
 
    if (!res.is_empty())
      return res;
 
    // No proper intersections — check containment.
    if (point_inside_ccw(vb, va(0)))
      {
        // A inside B → union is B.
        res.append(b);
        return res;
      }
    if (point_inside_ccw(va, vb(0)))
      {
        // B inside A → union is A.
        res.append(a);
        return res;
      }
    // Disjoint → both.
    res.append(a);
    res.append(b);
    return res;
  }
 
  static Array<Polygon> compute_difference(const Polygon &a, const Polygon &b)
  {
    Array<Point> va = extract(a);
    Array<Point> vb = extract(b);
    ensure_ccw(va);
    ensure_ccw(vb);
 
    // A \ B = A ∩ complement(B).  Reversing B's winding makes
    // "inside reversed-B" = "outside B", so intersection with
    // reversed-B gives the difference.
    reverse_array(vb);
 
    Array<Polygon> res = greiner_hormann(va, vb, /*start_entering=*/true);
 
    if (!res.is_empty())
      return res;
 
    // No proper intersections — check containment using ORIGINAL B.
    // Reverse vb back to original orientation for the test.
    reverse_array(vb);
 
    if (point_inside_ccw(vb, va(0)))
      {
        // A entirely inside B → difference is empty.
        return res;
      }
    // B inside A → difference has a hole (limitation: return A).
    // Disjoint → difference is A.
    res.append(a);
    return res;
  }
};
 
// ============================================================================
// Serialization — WKT and GeoJSON
// ============================================================================
 
class GeomSerializer
{
  static std::string dbl(const Geom_Number &n)
  {
    std::ostringstream os;
    os << std::setprecision(15) << geom_number_to_double(n);
    return os.str();
  }
 
public:
  // ---- WKT (Well-Known Text) ----
 
  [[nodiscard]] static std::string to_wkt(const Point &p)
  {
    return "POINT (" + dbl(p.get_x()) + " " + dbl(p.get_y()) + ")";
  }
 
  [[nodiscard]] static std::string to_wkt(const Segment &s)
  {
    return "LINESTRING (" + dbl(s.get_src_point().get_x()) + " " + dbl(s.get_src_point().get_y()) +
      ", " + dbl(s.get_tgt_point().get_x()) + " " + dbl(s.get_tgt_point().get_y()) + ")";
  }
 
  [[nodiscard]] static std::string to_wkt(const Triangle &t)
  {
    auto pt = [](const Point &p)
      {
        return dbl(p.get_x()) + " " + dbl(p.get_y());
      };
    return "POLYGON ((" + pt(t.get_p1()) + ", " + pt(t.get_p2()) + ", " + pt(t.get_p3()) + ", " +
      pt(t.get_p1()) + "))";
  }
 
  [[nodiscard]] static std::string to_wkt(const Rectangle &r)
  {
    return "POLYGON ((" + dbl(r.get_xmin()) + " " + dbl(r.get_ymin()) + ", " + dbl(r.get_xmax()) +
      " " + dbl(r.get_ymin()) + ", " + dbl(r.get_xmax()) + " " + dbl(r.get_ymax()) + ", " +
      dbl(r.get_xmin()) + " " + dbl(r.get_ymax()) + ", " + dbl(r.get_xmin()) + " " +
      dbl(r.get_ymin()) + "))";
  }
 
  [[nodiscard]] static std::string to_wkt(const Polygon &poly)
  {
    std::ostringstream os;
    os << std::setprecision(15) << "POLYGON ((";
    bool first = true;
    Point first_pt;
    for (Polygon::Vertex_Iterator it(poly); it.has_curr(); it.next_ne())
      {
        const Point &v = it.get_current_vertex();
        if (first)
          {
            first_pt = v;
            first = false;
          }
        else
          os << ", ";
        os << geom_number_to_double(v.get_x()) << " " << geom_number_to_double(v.get_y());
      }
    if (not first)
      os << ", " << geom_number_to_double(first_pt.get_x()) << " "
         << geom_number_to_double(first_pt.get_y());
    os << "))";
    return os.str();
  }
 
  [[nodiscard]] static std::string to_wkt(const Point3D &p)
  {
    return "POINT Z (" + dbl(p.get_x()) + " " + dbl(p.get_y()) + " " + dbl(p.get_z()) + ")";
  }
 
  // ---- GeoJSON ----
 
  [[nodiscard]] static std::string to_geojson(const Point &p)
  {
    return R"({"type":"Point","coordinates":[)" + dbl(p.get_x()) + "," + dbl(p.get_y()) + "]}";
  }
 
  [[nodiscard]] static std::string to_geojson(const Segment &s)
  {
    return R"({"type":"LineString","coordinates":[[)" + dbl(s.get_src_point().get_x()) + "," +
      dbl(s.get_src_point().get_y()) + "],[" + dbl(s.get_tgt_point().get_x()) + "," +
      dbl(s.get_tgt_point().get_y()) + "]]}";
  }
 
  [[nodiscard]] static std::string to_geojson(const Triangle &t)
  {
    auto pt = [](const Point &p)
      {
        return "[" + dbl(p.get_x()) + "," + dbl(p.get_y()) + "]";
      };
    return R"({"type":"Polygon","coordinates":[[)" + pt(t.get_p1()) + "," + pt(t.get_p2()) + "," +
      pt(t.get_p3()) + "," + pt(t.get_p1()) + "]]}";
  }
 
  [[nodiscard]] static std::string to_geojson(const Polygon &poly)
  {
    std::ostringstream os;
    os << std::setprecision(15);
    os << R"({"type":"Polygon","coordinates":[[)";
    bool first = true;
    Point first_pt;
    for (Polygon::Vertex_Iterator it(poly); it.has_curr(); it.next_ne())
      {
        const Point &v = it.get_current_vertex();
        if (first)
          {
            first_pt = v;
            first = false;
          }
        else
          os << ",";
        os << "[" << geom_number_to_double(v.get_x()) << "," << geom_number_to_double(v.get_y())
           << "]";
      }
    if (not first)
      os << ",[" << geom_number_to_double(first_pt.get_x()) << ","
         << geom_number_to_double(first_pt.get_y()) << "]";
    os << "]]}";
    return os.str();
  }
 
  [[nodiscard]] static std::string to_geojson(const Point3D &p)
  {
    return R"({"type":"Point","coordinates":[)" + dbl(p.get_x()) + "," + dbl(p.get_y()) + "," +
      dbl(p.get_z()) + "]}";
  }
};
 
// ============================================================================
// AABB Tree — Axis-Aligned Bounding Box Tree
// ============================================================================
 
class AABBTree
{
public:
  struct Entry
  {
    Rectangle bbox;  
    size_t index;    
  };
 
  struct DebugNode
  {
    size_t node_index = ~static_cast<size_t>(0);   
    Rectangle bbox;                                
    bool is_leaf = false;                          
    size_t entry_index = ~static_cast<size_t>(0);  
    size_t user_index = ~static_cast<size_t>(0);   
    size_t left = ~static_cast<size_t>(0);         
    size_t right = ~static_cast<size_t>(0);        
    size_t depth = 0;                              
  };
 
  struct DebugSnapshot
  {
    Array<DebugNode> nodes;                 
    size_t root = ~static_cast<size_t>(0);  
  };
 
private:
  struct Node
  {
    Rectangle bbox;                              
    size_t left = ~static_cast<size_t>(0);       
    size_t right = ~static_cast<size_t>(0);      
    size_t entry_idx = ~static_cast<size_t>(0);  
 
    [[nodiscard]] bool is_leaf() const
    {
      return entry_idx != ~static_cast<size_t>(0);
    }
  };
 
  Array<Node> nodes_;     
  Array<Entry> entries_;  
 
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  [[nodiscard]] static Rectangle union_bbox(const Rectangle &a, const Rectangle &b)
  {
    const Geom_Number xmin = a.get_xmin() < b.get_xmin() ? a.get_xmin() : b.get_xmin();
    const Geom_Number ymin = a.get_ymin() < b.get_ymin() ? a.get_ymin() : b.get_ymin();
    const Geom_Number xmax = a.get_xmax() > b.get_xmax() ? a.get_xmax() : b.get_xmax();
    const Geom_Number ymax = a.get_ymax() > b.get_ymax() ? a.get_ymax() : b.get_ymax();
    return {xmin, ymin, xmax, ymax};
  }
 
  [[nodiscard]] static bool boxes_overlap(const Rectangle &a, const Rectangle &b)
  {
    return a.get_xmin() <= b.get_xmax() and a.get_xmax() >= b.get_xmin() and
      a.get_ymin() <= b.get_ymax() and a.get_ymax() >= b.get_ymin();
  }
 
  [[nodiscard]] static bool box_contains_point(const Rectangle &r, const Point &p)
  {
    return p.get_x() >= r.get_xmin() and p.get_x() <= r.get_xmax() and p.get_y() >= r.get_ymin() and
      p.get_y() <= r.get_ymax();
  }
 
  [[nodiscard]] Geom_Number center_coord(const size_t entry_idx, const bool split_x) const
  {
    return split_x ? entries_(entry_idx).bbox.get_xmin() + entries_(entry_idx).bbox.get_xmax()
                   : entries_(entry_idx).bbox.get_ymin() + entries_(entry_idx).bbox.get_ymax();
  }
 
  void insertion_sort_by_center(Array<size_t> &idx,
                                const size_t lo,
                                const size_t hi,
                                const bool split_x) const
  {
    for (size_t i = lo + 1; i < hi; ++i)
      {
        const size_t key = idx(i);
        const Geom_Number key_val = center_coord(key, split_x);
        size_t j = i;
        while (j > lo and center_coord(idx(j - 1), split_x) > key_val)
          {
            idx(j) = idx(j - 1);
            --j;
          }
        idx(j) = key;
      }
  }
 
  // Partially reorder idx[lo..hi) so idx[kth] is in its sorted position
  // by center along the split axis (expected linear time).
  void select_kth_by_center(Array<size_t> &idx,
                            size_t lo,
                            size_t hi,
                            const size_t kth,
                            const bool split_x) const
  {
    while (hi - lo > 16)
      {
        const Geom_Number pivot = center_coord(idx(lo + (hi - lo) / 2), split_x);
 
        size_t lt = lo;
        size_t i = lo;
        size_t gt = hi;
        while (i < gt)
          {
            const Geom_Number val = center_coord(idx(i), split_x);
            if (val < pivot)
              {
                const size_t tmp = idx(lt);
                idx(lt) = idx(i);
                idx(i) = tmp;
                ++lt;
                ++i;
              }
            else if (val > pivot)
              {
                --gt;
                const size_t tmp = idx(gt);
                idx(gt) = idx(i);
                idx(i) = tmp;
              }
            else
              ++i;
          }
 
        if (kth < lt)
          hi = lt;
        else if (kth >= gt)
          lo = gt;
        else
          return;
      }
 
    insertion_sort_by_center(idx, lo, hi, split_x);
  }
 
  // Build a subtree for entries[lo..hi) and return its node index.
  size_t build(Array<size_t> &idx, const size_t lo, const size_t hi)
  {
    if (hi - lo == 1)
      {
        Node n;
        n.bbox = entries_(idx(lo)).bbox;
        n.entry_idx = idx(lo);
        const size_t ni = nodes_.size();
        nodes_.append(n);
        return ni;
      }
 
    // Compute enclosing bbox.
    Rectangle total = entries_(idx(lo)).bbox;
    for (size_t i = lo + 1; i < hi; ++i)
      total = union_bbox(total, entries_(idx(i)).bbox);
 
    // Split along the longest axis.
    const Geom_Number dx = total.get_xmax() - total.get_xmin();
    const Geom_Number dy = total.get_ymax() - total.get_ymin();
    const bool split_x = dx >= dy;
 
    const size_t mid = lo + (hi - lo) / 2;
    select_kth_by_center(idx, lo, hi, mid, split_x);
 
    const size_t left = build(idx, lo, mid);
    const size_t right = build(idx, mid, hi);
 
    Node n;
    n.bbox = union_bbox(nodes_(left).bbox, nodes_(right).bbox);
    n.left = left;
    n.right = right;
    const size_t ni = nodes_.size();
    nodes_.append(n);
    return ni;
  }
 
  void query_impl(const size_t ni, const Rectangle &q, Array<size_t> &results) const
  {
    if (ni == NONE)
      return;
    const Node &n = nodes_(ni);
    if (not boxes_overlap(n.bbox, q))
      return;
 
    if (n.is_leaf())
      {
        results.append(entries_(n.entry_idx).index);
        return;
      }
 
    query_impl(n.left, q, results);
    query_impl(n.right, q, results);
  }
 
  void query_point_impl(const size_t ni, const Point &p, Array<size_t> &results) const
  {
    if (ni == NONE)
      return;
    const Node &n = nodes_(ni);
    if (not box_contains_point(n.bbox, p))
      return;
 
    if (n.is_leaf())
      {
        if (box_contains_point(entries_(n.entry_idx).bbox, p))
          results.append(entries_(n.entry_idx).index);
        return;
      }
 
    query_point_impl(n.left, p, results);
    query_point_impl(n.right, p, results);
  }
 
  size_t root_ = NONE;
 
public:
  AABBTree() = default;
 
  void build(const Array<Entry> &entries)
  {
    entries_ = entries;
    nodes_ = Array<Node>();
    if (entries_.is_empty())
      {
        root_ = NONE;
        return;
      }
 
    Array<size_t> idx;
    idx.reserve(entries_.size());
    for (size_t i = 0; i < entries_.size(); ++i)
      idx.append(i);
 
    root_ = build(idx, 0, idx.size());
  }
 
  [[nodiscard]] Array<size_t> query(const Rectangle &query) const
  {
    Array<size_t> results;
    if (root_ != NONE)
      query_impl(root_, query, results);
    return results;
  }
 
  [[nodiscard]] Array<size_t> query_point(const Point &p) const
  {
    Array<size_t> results;
    if (root_ != NONE)
      query_point_impl(root_, p, results);
    return results;
  }
 
  [[nodiscard]] Rectangle root_bbox() const
  {
    ah_domain_error_if(root_ == NONE) << "Empty tree";
    return nodes_(root_).bbox;
  }
 
  [[nodiscard]] size_t size() const
  {
    return entries_.size();
  }
 
  [[nodiscard]] bool is_empty() const
  {
    return entries_.is_empty();
  }
 
  [[nodiscard]] DebugSnapshot debug_snapshot() const
  {
    DebugSnapshot snap;
    if (root_ == NONE)
      return snap;
 
    snap.nodes.reserve(nodes_.size());
 
    auto dfs = [&](const auto &self, const size_t ni, const size_t depth) -> size_t
      {
        const Node &n = nodes_(ni);
        const size_t out_idx = snap.nodes.size();
        snap.nodes.append(DebugNode{});
        snap.nodes(out_idx).node_index = ni;
        snap.nodes(out_idx).bbox = n.bbox;
        snap.nodes(out_idx).is_leaf = n.is_leaf();
        snap.nodes(out_idx).depth = depth;
        if (n.is_leaf())
          {
            snap.nodes(out_idx).entry_index = n.entry_idx;
            snap.nodes(out_idx).user_index = entries_(n.entry_idx).index;
          }
        else
          {
            const size_t left = self(self, n.left, depth + 1);
            const size_t right = self(self, n.right, depth + 1);
            snap.nodes(out_idx).left = left;
            snap.nodes(out_idx).right = right;
          }
        return out_idx;
      };
 
    snap.root = dfs(dfs, root_, 0);
    return snap;
  }
};
 
// ============================================================================
// Polyline / Polygon Simplification
// ============================================================================
 
class DouglasPeuckerSimplification
{
  static void dp_recurse(const Array<Point> &pts,
                         const size_t first,
                         const size_t last,
                         const Geom_Number &eps2,
                         Array<bool> &keep)
  {
    if (last <= first + 1)
      return;
 
    const Segment seg(pts(first), pts(last));
    Geom_Number max_dist2 = 0;
    size_t max_idx = first;
 
    for (size_t i = first + 1; i < last; ++i)
      {
        Geom_Number d = seg.distance_to(pts(i));
        if (Geom_Number d2 = d * d; d2 > max_dist2)
          {
            max_dist2 = d2;
            max_idx = i;
          }
      }
 
    if (max_dist2 > eps2)
      {
        keep(max_idx) = true;
        dp_recurse(pts, first, max_idx, eps2, keep);
        dp_recurse(pts, max_idx, last, eps2, keep);
      }
  }
 
public:
  [[nodiscard]] Array<Point> operator () (const Array<Point> &polyline, const Geom_Number &epsilon) const
  {
    const size_t n = polyline.size();
    if (n <= 2)
      return polyline;
 
    const Geom_Number eps2 = epsilon * epsilon;
    Array<bool> keep(n);
    for (size_t i = 0; i < n; ++i)
      keep.append(false);
    keep(0) = true;
    keep(n - 1) = true;
 
    dp_recurse(polyline, 0, n - 1, eps2, keep);
 
    Array<Point> result;
    for (size_t i = 0; i < n; ++i)
      if (keep(i))
        result.append(polyline(i));
 
    return result;
  }
 
  [[nodiscard]] Array<Point> operator () (const DynList<Point> &polyline,
                                          const Geom_Number &epsilon) const
  {
    Array<Point> arr;
    for (typename DynList<Point>::Iterator it(polyline); it.has_curr(); it.next_ne())
      arr.append(it.get_curr());
    return (*this)(arr, epsilon);
  }
 
  [[nodiscard]] Polygon simplify_polygon(const Polygon &poly, const Geom_Number &epsilon) const
  {
    auto verts = GeomPolygonUtils::extract_vertices(poly);
    const size_t n = verts.size();
    if (n <= 3)
      return poly;
 
    // Find vertex farthest from vertex 0
    size_t far_idx = 1;
    Geom_Number far_dist2 = 0;
    for (size_t i = 1; i < n; ++i)
      {
        Geom_Number dx = verts(i).get_x() - verts(0).get_x();
        Geom_Number dy = verts(i).get_y() - verts(0).get_y();
        if (Geom_Number d2 = dx * dx + dy * dy; d2 > far_dist2)
          {
            far_dist2 = d2;
            far_idx = i;
          }
      }
 
    // Build two open chains sharing endpoints at vertex 0 and far_idx
    Array<Point> chain1;  // 0 → far_idx
    for (size_t i = 0; i <= far_idx; ++i)
      chain1.append(verts(i));
 
    Array<Point> chain2;  // far_idx → 0 (wrapping around)
    for (size_t i = far_idx; i < n; ++i)
      chain2.append(verts(i));
    chain2.append(verts(0));
 
    auto s1 = (*this)(chain1, epsilon);
    auto s2 = (*this)(chain2, epsilon);
 
    // Merge: s1 + s2 without duplicate junction points
    Array<Point> merged;
    for (size_t i = 0; i < s1.size(); ++i)
      merged.append(s1(i));
    for (size_t i = 1; i + 1 < s2.size(); ++i)  // skip first (dup) & last (dup)
      merged.append(s2(i));
 
    if (merged.size() < 3)
      return poly;
 
    Polygon result;
    for (size_t i = 0; i < merged.size(); ++i)
      result.add_vertex(merged(i));
    result.close();
    return result;
  }
};
 
class VisvalingamWhyattSimplification
{
  struct VWEntry
  {
    size_t idx;        
    Geom_Number area;  
 
    bool operator < (const VWEntry &o) const
    {
      return area < o.area;
    }
    bool operator > (const VWEntry &o) const
    {
      return area > o.area;
    }
  };
 
  [[nodiscard]] static Geom_Number effective_area(const Point &a, const Point &b, const Point &c)
  {
    Geom_Number ap = area_of_parallelogram(a, b, c);
    if (ap < 0)
      ap = -ap;
    return ap / 2;
  }
 
  [[nodiscard]] static Array<Point> simplify_open_array(const Array<Point> &polyline,
                                                        const Geom_Number &area_threshold)
  {
    const size_t n = polyline.size();
    if (n <= 2)
      return polyline;
 
    // prev/next linked list (index-based)
    Array<size_t> prev(n), next(n);
    Array<bool> alive(n);
    for (size_t i = 0; i < n; ++i)
      {
        prev.append(i == 0 ? n : i - 1);  // n = sentinel for "no prev"
        next.append(i == n - 1 ? n : i + 1);
        alive.append(true);
      }
 
    // Min-heap
    DynBinHeap<VWEntry, std::less<>> heap;
 
    // Compute initial areas for interior vertices
    Array<Geom_Number> areas(n);
    for (size_t i = 0; i < n; ++i)
      areas.append(Geom_Number(-1));
 
    for (size_t i = 1; i + 1 < n; ++i)
      {
        areas(i) = effective_area(polyline(prev(i)), polyline(i), polyline(next(i)));
        heap.put({i, areas(i)});
      }
 
    while (not heap.is_empty())
      {
        auto [idx, area] = heap.get();
 
        if (not alive(idx))
          continue;
        if (area != areas(idx))
          continue;  // stale entry
        if (area >= area_threshold)
          break;
 
        // Remove this vertex
        alive(idx) = false;
        const size_t p = prev(idx);
        const size_t nx = next(idx);
 
        if (p < n)
          next(p) = nx;
        if (nx < n)
          prev(nx) = p;
 
        // Recompute neighbor areas
        if (p < n and p != 0 and prev(p) < n)
          {
            areas(p) = effective_area(polyline(prev(p)), polyline(p), polyline(next(p)));
            heap.put({p, areas(p)});
          }
        if (nx < n and nx != n - 1 and next(nx) < n)
          {
            areas(nx) = effective_area(polyline(prev(nx)), polyline(nx), polyline(next(nx)));
            heap.put({nx, areas(nx)});
          }
      }
 
    Array<Point> result;
    for (size_t i = 0; i < n; ++i)
      if (alive(i))
        result.append(polyline(i));
 
    return result;
  }
 
public:
  [[nodiscard]] Array<Point> operator () (const Array<Point> &polyline,
                                          const Geom_Number &area_threshold) const
  {
    return simplify_open_array(polyline, area_threshold);
  }
 
  [[nodiscard]] Array<Point> operator () (const DynList<Point> &polyline,
                                          const Geom_Number &area_threshold) const
  {
    Array<Point> arr;
    for (typename DynList<Point>::Iterator it(polyline); it.has_curr(); it.next_ne())
      arr.append(it.get_curr());
    return simplify_open_array(arr, area_threshold);
  }
 
  [[nodiscard]] static Polygon simplify_polygon(const Polygon &poly, const Geom_Number &area_threshold)
  {
    auto verts = GeomPolygonUtils::extract_vertices(poly);
    const size_t n = verts.size();
    if (n <= 3)
      return poly;
 
    // Cyclic prev/next linked list
    Array<size_t> prev(n), next(n);
    Array<bool> alive(n);
    for (size_t i = 0; i < n; ++i)
      {
        prev.append(i == 0 ? n - 1 : i - 1);
        next.append(i == n - 1 ? 0 : i + 1);
        alive.append(true);
      }
 
    DynBinHeap<VWEntry, std::less<>> heap;
 
    Array<Geom_Number> areas(n);
    for (size_t i = 0; i < n; ++i)
      {
        areas.append(effective_area(verts(prev(i)), verts(i), verts(next(i))));
        heap.put({i, areas(i)});
      }
 
    size_t remaining = n;
    while (not heap.is_empty() and remaining > 3)
      {
        auto [idx, area] = heap.get();
 
        if (not alive(idx))
          continue;
        if (area != areas(idx))
          continue;
        if (area >= area_threshold)
          break;
 
        alive(idx) = false;
        --remaining;
        const size_t p = prev(idx);
        const size_t nx = next(idx);
 
        next(p) = nx;
        prev(nx) = p;
 
        // Recompute neighbor areas
        areas(p) = effective_area(verts(prev(p)), verts(p), verts(next(p)));
        heap.put({p, areas(p)});
        areas(nx) = effective_area(verts(prev(nx)), verts(nx), verts(next(nx)));
        heap.put({nx, areas(nx)});
      }
 
    Array<Point> result;
    for (size_t i = 0; i < n; ++i)
      if (alive(i))
        result.append(verts(i));
 
    if (result.size() < 3)
      return poly;
 
    Polygon rpoly;
    for (size_t i = 0; i < result.size(); ++i)
      rpoly.add_vertex(result(i));
    rpoly.close();
    return rpoly;
  }
};
 
// ============================================================================
// Chaikin Corner-Cutting Subdivision (Polygon Smoothing)
// ============================================================================
 
class ChaikinSmoothing
{
  [[nodiscard]] static Array<Point> smooth_open_once(const Array<Point> &pts, const Geom_Number &r)
  {
    const size_t n = pts.size();
    Array<Point> result;
    result.append(pts(0));
    for (size_t i = 0; i + 1 < n; ++i)
      {
        const auto &p = pts(i);
        const auto &q = pts(i + 1);
        Geom_Number one_r = Geom_Number(1) - r;
        result.append(Point(p.get_x() * one_r + q.get_x() * r, p.get_y() * one_r + q.get_y() * r));
        result.append(Point(p.get_x() * r + q.get_x() * one_r, p.get_y() * r + q.get_y() * one_r));
      }
    result.append(pts(n - 1));
    return result;
  }
 
  [[nodiscard]] static Array<Point> smooth_closed_once(const Array<Point> &pts, const Geom_Number &r)
  {
    const size_t n = pts.size();
    Array<Point> result;
    Geom_Number one_r = Geom_Number(1) - r;
    for (size_t i = 0; i < n; ++i)
      {
        const auto &p = pts(i);
        const auto &q = pts((i + 1) % n);
        result.append(Point(p.get_x() * one_r + q.get_x() * r, p.get_y() * one_r + q.get_y() * r));
        result.append(Point(p.get_x() * r + q.get_x() * one_r, p.get_y() * r + q.get_y() * one_r));
      }
    return result;
  }
 
public:
  [[nodiscard]] Array<Point> operator () (const Array<Point> &polyline,
                                          size_t iterations,
                                          const Geom_Number &ratio = Geom_Number(1, 4)) const
  {
    ah_domain_error_if(iterations == 0) << "iterations must be >= 1";
    ah_domain_error_if(ratio <= Geom_Number(0) or ratio >= Geom_Number(1, 2))
      << "ratio must be in (0, 0.5)";
 
    Array<Point> cur = polyline;
    for (size_t k = 0; k < iterations; ++k)
      cur = smooth_open_once(cur, ratio);
    return cur;
  }
 
  [[nodiscard]] Array<Point> operator () (const DynList<Point> &polyline,
                                          size_t iterations,
                                          const Geom_Number &ratio = Geom_Number(1, 4)) const
  {
    Array<Point> arr;
    for (typename DynList<Point>::Iterator it(polyline); it.has_curr(); it.next_ne())
      arr.append(it.get_curr());
    return (*this)(arr, iterations, ratio);
  }
 
  [[nodiscard]] static Polygon smooth_polygon(const Polygon &poly,
                                              size_t iterations,
                                              const Geom_Number &ratio = Geom_Number(1, 4))
  {
    ah_domain_error_if(iterations == 0) << "iterations must be >= 1";
    ah_domain_error_if(ratio <= Geom_Number(0) or ratio >= Geom_Number(1, 2))
      << "ratio must be in (0, 0.5)";
 
    Array<Point> cur = GeomPolygonUtils::extract_vertices(poly);
    for (size_t k = 0; k < iterations; ++k)
      cur = smooth_closed_once(cur, ratio);
 
    Polygon rpoly;
    for (size_t i = 0; i < cur.size(); ++i)
      rpoly.add_vertex(cur(i));
    rpoly.close();
    return rpoly;
  }
};
 
// ============================================================================
// Trapezoidal Map Point Location
// ============================================================================
 
class TrapezoidalMapPointLocation
{
public:
  static constexpr size_t NONE = ~static_cast<size_t>(0);
 
  struct Trapezoid
  {
    size_t top;          
    size_t bottom;       
    size_t leftp;        
    size_t rightp;       
    size_t upper_left;   
    size_t lower_left;   
    size_t upper_right;  
    size_t lower_right;  
    size_t dag_leaf;     
    bool active;         
  };
 
  enum class NodeType
  {
    X_NODE,  
    Y_NODE,  
    LEAF     
  };
 
  struct DagNode
  {
    NodeType type;  
    size_t index;   
    size_t left;    
    size_t right;   
  };
 
  enum class LocationType
  {
    TRAPEZOID,   
    ON_SEGMENT,  
    ON_POINT     
  };
 
  struct LocationResult
  {
    LocationType type;       
    size_t trapezoid_index;  
    size_t segment_index;    
    size_t point_index;      
  };
 
  struct Result
  {
    Array<Point> points;          
    Array<Segment> segments;      
    Array<Trapezoid> trapezoids;  
    Array<DagNode> dag;           
    size_t dag_root;              
    size_t num_input_segments;    
    size_t num_input_points;      
 
    [[nodiscard]] LocationResult locate(const Point &p) const
    {
      size_t ni = dag_root;
      while (true)
        {
          const auto &[type, index, left, right] = dag(ni);
          if (type == NodeType::LEAF)
            return {LocationType::TRAPEZOID, index, NONE, NONE};
 
          if (type == NodeType::X_NODE)
            {
              const Point &xp = points(index);
              if (p == xp)
                return {LocationType::ON_POINT, NONE, NONE, index};
              ni = p < xp ? left : right;
            }
          else  // Y_NODE
            {
              const Segment &seg = segments(index);
              const Geom_Number cross =
                area_of_parallelogram(seg.get_src_point(), seg.get_tgt_point(), p);
              if (cross == 0)
                {
                  // the point is on the segment line — check if between endpoints
                  if (seg.contains(p))
                    return {LocationType::ON_SEGMENT, NONE, index, NONE};
                  // collinear but outside the segment extent — go above
                  ni = left;
                }
              else if (cross > 0)
                ni = left;  // above (left of directed segment)
              else
                ni = right;  // below
            }
        }
    }
 
    [[nodiscard]] bool contains(const Point &p) const
    {
      // Check exact boundary / vertex hits first.
      for (size_t i = 0; i < num_input_points; ++i)
        if (p == points(i))
          return true;
      for (size_t i = 0; i < num_input_segments; ++i)
        if (segments(i).contains(p))
          return true;
 
      // Vertical ray cast downward: count input segments strictly below p
      // whose x-range covers p.x (half-open [src.x, tgt.x)).
      // Segments are stored left-to-right (src < tgt), so src.x <= tgt.x.
      // Vertical segments have empty half-open interval and are skipped.
      size_t crossings = 0;
      for (size_t i = 0; i < num_input_segments; ++i)
        {
          const Segment &seg = segments(i);
          const Point &a = seg.get_src_point();
          const Point &b = seg.get_tgt_point();
          if (p.get_x() < a.get_x() or p.get_x() >= b.get_x())
            continue;
          // y of segment at p.x (b.x != a.x guaranteed by half-open check)
          const Geom_Number seg_y =
            a.get_y() + (b.get_y() - a.get_y()) * (p.get_x() - a.get_x()) / (b.get_x() - a.get_x());
          if (seg_y < p.get_y())
            ++crossings;
        }
      return crossings % 2 == 1;
    }
  };
 
private:
  [[nodiscard]] static bool point_above_segment(const Point &p, const Segment &seg)
  {
    return area_of_parallelogram(seg.get_src_point(), seg.get_tgt_point(), p) > 0;
  }
 
  [[nodiscard]] static size_t dag_locate(const Array<Point> &pts,
                                         const Array<Segment> &segs,
                                         const Array<DagNode> &dag,
                                         const Point &p,
                                         size_t root)
  {
    size_t ni = root;
    while (true)
      {
        const auto &[type, index, left, right] = dag(ni);
        if (type == NodeType::LEAF)
          return index;
 
        if (type == NodeType::X_NODE)
          {
            if (const Point &xp = pts(index); p == xp)
              ni = right;  // tie-break: go right
            else
              ni = p < xp ? left : right;
          }
        else  // Y_NODE
          {
            const Geom_Number cross =
              area_of_parallelogram(segs(index).get_src_point(), segs(index).get_tgt_point(), p);
            if (cross > 0)
              ni = left;  // above
            else if (cross < 0)
              ni = right;  // below
            else
              ni = left;  // on segment line → go above
          }
      }
  }
 
  static size_t make_trapezoid(Array<Trapezoid> &traps,
                               Array<DagNode> &dag,
                               const size_t top,
                               const size_t bottom,
                               const size_t leftp,
                               const size_t rightp)
  {
    const size_t ti = traps.size();
    const size_t di = dag.size();
    traps.append(Trapezoid{top, bottom, leftp, rightp, NONE, NONE, NONE, NONE, di, true});
    dag.append(DagNode{NodeType::LEAF, ti, NONE, NONE});
    return ti;
  }
 
  static void replace_leaf(Array<DagNode> &dag,
                           const size_t leaf_idx,
                           const NodeType type,
                           const size_t index,
                           const size_t left,
                           const size_t right)
  {
    dag(leaf_idx).type = type;
    dag(leaf_idx).index = index;
    dag(leaf_idx).left = left;
    dag(leaf_idx).right = right;
  }
 
  static void update_neighbor(Array<Trapezoid> &traps,
                              const size_t neighbor_idx,
                              const size_t old_ti,
                              const size_t new_ti)
  {
    if (neighbor_idx == NONE)
      return;
    Trapezoid &nb = traps(neighbor_idx);
    if (nb.upper_left == old_ti)
      nb.upper_left = new_ti;
    if (nb.lower_left == old_ti)
      nb.lower_left = new_ti;
    if (nb.upper_right == old_ti)
      nb.upper_right = new_ti;
    if (nb.lower_right == old_ti)
      nb.lower_right = new_ti;
  }
 
  [[nodiscard]] static Array<size_t> find_crossed_trapezoids(const Array<Point> &pts,
                                                             const Array<Segment> &segs,
                                                             const Array<Trapezoid> &traps,
                                                             const size_t seg_idx,
                                                             const size_t start_trap)
  {
    Array<size_t> crossed;
    crossed.append(start_trap);
 
    const Segment &seg = segs(seg_idx);
    const Point &rp = seg.get_tgt_point();
 
    size_t ti = start_trap;
    while (true)
      {
        const Trapezoid &t = traps(ti);
        const Point &rightp = pts(t.rightp);
        // If the right boundary of this trapezoid is at or past the
        // segment's right endpoint, we're done.
        if (rp < rightp or rp == rightp)
          break;
 
        // Go right: the segment exits through the right wall of t.
        // If the right endpoint of the segment is above the segment
        // at the right boundary x, go to upper_right; else lower_right.
        if (t.upper_right != NONE and t.lower_right != NONE)
          {
            // Test which neighbor the segment enters.
            if (point_above_segment(rightp, seg))
              ti = t.lower_right;
            else
              ti = t.upper_right;
          }
        else if (t.upper_right != NONE)
          ti = t.upper_right;
        else if (t.lower_right != NONE)
          ti = t.lower_right;
        else
          break;  // no right neighbor
 
        crossed.append(ti);
      }
    return crossed;
  }
 
  static void split_single_trapezoid(Array<Point> &pts,
                                     Array<Segment> &segs,
                                     Array<Trapezoid> &traps,
                                     Array<DagNode> &dag,
                                     const size_t seg_idx,
                                     const size_t trap_idx)
  {
    const Trapezoid old_t = traps(trap_idx);
    const Segment &seg = segs(seg_idx);
    const Point &lp = seg.get_src_point();
    const Point &rp = seg.get_tgt_point();
 
    // Find point indices.
    size_t lp_idx = NONE, rp_idx = NONE;
    for (size_t i = 0; i < pts.size(); ++i)
      {
        if (pts(i) == lp)
          lp_idx = i;
        if (pts(i) == rp)
          rp_idx = i;
      }
 
    const bool shared_left = (old_t.leftp == lp_idx);
    const bool shared_right = (old_t.rightp == rp_idx);
 
    // Deactivate old trapezoid.
    traps(trap_idx).active = false;
 
    // Create new trapezoids:
    // A = left of lp (if not shared)
    // B = above segment (between lp and rp)
    // C = below segment (between lp and rp)
    // D = right of rp (if not shared)
 
    const size_t dag_old = old_t.dag_leaf;
 
    size_t a_idx = NONE, d_idx = NONE;
 
    if (not shared_left)
      a_idx = make_trapezoid(traps, dag, old_t.top, old_t.bottom, old_t.leftp, lp_idx);
    const size_t b_idx = make_trapezoid(traps, dag, old_t.top, seg_idx, lp_idx, rp_idx);
    const size_t c_idx = make_trapezoid(traps, dag, seg_idx, old_t.bottom, lp_idx, rp_idx);
    if (not shared_right)
      d_idx = make_trapezoid(traps, dag, old_t.top, old_t.bottom, rp_idx, old_t.rightp);
 
    // Set neighbor pointers.
    // A neighbors:
    if (a_idx != NONE)
      {
        traps(a_idx).upper_left = old_t.upper_left;
        traps(a_idx).lower_left = old_t.lower_left;
        traps(a_idx).upper_right = b_idx;
        traps(a_idx).lower_right = c_idx;
        update_neighbor(traps, old_t.upper_left, trap_idx, a_idx);
        update_neighbor(traps, old_t.lower_left, trap_idx, a_idx);
      }
 
    // B neighbors:
    traps(b_idx).upper_left = shared_left ? old_t.upper_left : a_idx;
    traps(b_idx).lower_left = shared_left ? old_t.lower_left : a_idx;
    traps(b_idx).upper_right = shared_right ? old_t.upper_right : d_idx;
    traps(b_idx).lower_right = shared_right ? old_t.lower_right : d_idx;
 
    // C neighbors:
    traps(c_idx).upper_left = shared_left ? old_t.upper_left : a_idx;
    traps(c_idx).lower_left = shared_left ? old_t.lower_left : a_idx;
    traps(c_idx).upper_right = shared_right ? old_t.upper_right : d_idx;
    traps(c_idx).lower_right = shared_right ? old_t.lower_right : d_idx;
 
    if (shared_left)
      {
        update_neighbor(traps, old_t.upper_left, trap_idx, b_idx);
        update_neighbor(traps, old_t.lower_left, trap_idx, c_idx);
      }
 
    // D neighbors:
    if (d_idx != NONE)
      {
        traps(d_idx).upper_left = b_idx;
        traps(d_idx).lower_left = c_idx;
        traps(d_idx).upper_right = old_t.upper_right;
        traps(d_idx).lower_right = old_t.lower_right;
        update_neighbor(traps, old_t.upper_right, trap_idx, d_idx);
        update_neighbor(traps, old_t.lower_right, trap_idx, d_idx);
      }
 
    if (shared_right)
      {
        update_neighbor(traps, old_t.upper_right, trap_idx, b_idx);
        update_neighbor(traps, old_t.lower_right, trap_idx, c_idx);
      }
 
    // Build DAG sub-tree rooted at dag_old.
    // Structure depends on shared_left / shared_right.
    if (not shared_left and not shared_right)
      {
        // X(lp) -> left=A, right=X(rp) -> left=Y(seg)->above=B,below=C, right=D
        const size_t y_node = dag.size();
        dag.append(DagNode{NodeType::Y_NODE, seg_idx, traps(b_idx).dag_leaf, traps(c_idx).dag_leaf});
        const size_t x_rp = dag.size();
        dag.append(DagNode{NodeType::X_NODE, rp_idx, y_node, traps(d_idx).dag_leaf});
        replace_leaf(dag, dag_old, NodeType::X_NODE, lp_idx, traps(a_idx).dag_leaf, x_rp);
      }
    else if (shared_left and not shared_right)
      {
        // Y(seg) -> above=B, below=C  wrapped in X(rp)->left=Y, right=D
        const size_t y_node = dag.size();
        dag.append(DagNode{NodeType::Y_NODE, seg_idx, traps(b_idx).dag_leaf, traps(c_idx).dag_leaf});
        replace_leaf(dag, dag_old, NodeType::X_NODE, rp_idx, y_node, traps(d_idx).dag_leaf);
      }
    else if (not shared_left and shared_right)
      {
        // X(lp) -> left=A, right=Y(seg)->above=B, below=C
        const size_t y_node = dag.size();
        dag.append(DagNode{NodeType::Y_NODE, seg_idx, traps(b_idx).dag_leaf, traps(c_idx).dag_leaf});
        replace_leaf(dag, dag_old, NodeType::X_NODE, lp_idx, traps(a_idx).dag_leaf, y_node);
      }
    else  // both shared
      {
        // Just Y(seg) -> above=B, below=C
        replace_leaf(dag, dag_old, NodeType::Y_NODE, seg_idx, traps(b_idx).dag_leaf,
                     traps(c_idx).dag_leaf);
      }
  }
 
  static void split_multiple_trapezoids(Array<Point> &pts,
                                        Array<Segment> &segs,
                                        Array<Trapezoid> &traps,
                                        Array<DagNode> &dag,
                                        const size_t seg_idx,
                                        const Array<size_t> &crossed)
  {
    const Segment &seg = segs(seg_idx);
    const Point &lp = seg.get_src_point();
    const Point &rp = seg.get_tgt_point();
 
    size_t lp_idx = NONE, rp_idx = NONE;
    for (size_t i = 0; i < pts.size(); ++i)
      {
        if (pts(i) == lp)
          lp_idx = i;
        if (pts(i) == rp)
          rp_idx = i;
      }
 
    const size_t nc = crossed.size();
 
    // For each crossed trapezoid, create above/below sub-trapezoids.
    // Adjacent above (or below) trapezoids that share the same top (or
    // bottom) segment are merged.
    Array<size_t> above_traps;  // one per crossed, but may be merged
    Array<size_t> below_traps;
    above_traps.reserve(nc);
    below_traps.reserve(nc);
 
    size_t prev_above = NONE, prev_below = NONE;
    size_t left_trap = NONE;  // left-of-lp trapezoid
 
    for (size_t ci = 0; ci < nc; ++ci)
      {
        const size_t ti = crossed(ci);
        const Trapezoid old_t = traps(ti);
        traps(ti).active = false;
 
        const bool is_first = (ci == 0);
        const bool is_last = (ci == nc - 1);
        const bool shared_left = is_first and (old_t.leftp == lp_idx);
        const bool shared_right = is_last and (old_t.rightp == rp_idx);
 
        // Determine the left/right x-boundaries for the new sub-trapezoids.
        const size_t new_leftp = is_first ? lp_idx : old_t.leftp;
        const size_t new_rightp = is_last ? rp_idx : old_t.rightp;
 
        // Above trapezoid.
        bool merged_above = false;
        if (prev_above != NONE and traps(prev_above).top == old_t.top)
          {
            // Merge: extend prev_above to the right.
            traps(prev_above).rightp = new_rightp;
            above_traps.append(prev_above);
            merged_above = true;
          }
        else
          {
            const size_t ai = make_trapezoid(traps, dag, old_t.top, seg_idx, new_leftp, new_rightp);
            above_traps.append(ai);
            prev_above = ai;
          }
 
        // Below trapezoid.
        bool merged_below = false;
        if (prev_below != NONE and traps(prev_below).bottom == old_t.bottom)
          {
            traps(prev_below).rightp = new_rightp;
            below_traps.append(prev_below);
            merged_below = true;
          }
        else
          {
            const size_t bi =
              make_trapezoid(traps, dag, seg_idx, old_t.bottom, new_leftp, new_rightp);
            below_traps.append(bi);
            prev_below = bi;
          }
 
        const size_t cur_above = above_traps(ci);
        const size_t cur_below = below_traps(ci);
 
        // Handle the left trapezoid (only for the first crossed trapezoid).
        if (is_first and not shared_left)
          {
            left_trap = make_trapezoid(traps, dag, old_t.top, old_t.bottom, old_t.leftp, lp_idx);
            traps(left_trap).upper_left = old_t.upper_left;
            traps(left_trap).lower_left = old_t.lower_left;
            traps(left_trap).upper_right = cur_above;
            traps(left_trap).lower_right = cur_below;
            update_neighbor(traps, old_t.upper_left, ti, left_trap);
            update_neighbor(traps, old_t.lower_left, ti, left_trap);
          }
 
        // Set left neighbors for above/below.
        if (is_first)
          {
            if (not merged_above)
              {
                if (shared_left)
                  {
                    traps(cur_above).upper_left = old_t.upper_left;
                    traps(cur_above).lower_left = old_t.lower_left;
                    update_neighbor(traps, old_t.upper_left, ti, cur_above);
                  }
                else
                  {
                    traps(cur_above).upper_left = left_trap;
                    traps(cur_above).lower_left = left_trap;
                  }
              }
            if (not merged_below)
              {
                if (shared_left)
                  {
                    traps(cur_below).upper_left = old_t.upper_left;
                    traps(cur_below).lower_left = old_t.lower_left;
                    update_neighbor(traps, old_t.lower_left, ti, cur_below);
                  }
                else
                  {
                    traps(cur_below).upper_left = left_trap;
                    traps(cur_below).lower_left = left_trap;
                  }
              }
          }
        else
          {
            // Interior crossed trapezoid.
            if (not merged_above)
              {
                // Left neighbor of new above is the previous above.
                traps(cur_above).upper_left = above_traps(ci - 1);
                traps(cur_above).lower_left = above_traps(ci - 1);
                // Also set the previous above's right neighbors.
                if (above_traps(ci - 1) != cur_above)
                  {
                    traps(above_traps(ci - 1)).upper_right = cur_above;
                    traps(above_traps(ci - 1)).lower_right = cur_above;
                  }
              }
            if (not merged_below)
              {
                traps(cur_below).upper_left = below_traps(ci - 1);
                traps(cur_below).lower_left = below_traps(ci - 1);
                if (below_traps(ci - 1) != cur_below)
                  {
                    traps(below_traps(ci - 1)).upper_right = cur_below;
                    traps(below_traps(ci - 1)).lower_right = cur_below;
                  }
              }
 
            // Connect left neighbors from old trapezoid.
            if (not merged_above)
              if (old_t.upper_left != NONE and old_t.upper_left != crossed(ci - 1))
                {
                  traps(cur_above).upper_left = old_t.upper_left;
                  update_neighbor(traps, old_t.upper_left, ti, cur_above);
                }
            if (not merged_below)
              if (old_t.lower_left != NONE and old_t.lower_left != crossed(ci - 1))
                {
                  traps(cur_below).lower_left = old_t.lower_left;
                  update_neighbor(traps, old_t.lower_left, ti, cur_below);
                }
          }
 
        // Handle right trapezoid (only for last crossed trapezoid).
        if (is_last)
          {
            if (not shared_right)
              {
                const size_t right_trap =
                  make_trapezoid(traps, dag, old_t.top, old_t.bottom, rp_idx, old_t.rightp);
                traps(right_trap).upper_left = cur_above;
                traps(right_trap).lower_left = cur_below;
                traps(right_trap).upper_right = old_t.upper_right;
                traps(right_trap).lower_right = old_t.lower_right;
                update_neighbor(traps, old_t.upper_right, ti, right_trap);
                update_neighbor(traps, old_t.lower_right, ti, right_trap);
                traps(cur_above).upper_right = right_trap;
                traps(cur_above).lower_right = right_trap;
                traps(cur_below).upper_right = right_trap;
                traps(cur_below).lower_right = right_trap;
 
                // Build DAG for this trapezoid.
                const size_t y_node = dag.size();
                dag.append(DagNode{NodeType::Y_NODE, seg_idx, traps(cur_above).dag_leaf,
                                   traps(cur_below).dag_leaf});
                const size_t dag_old = old_t.dag_leaf;
                replace_leaf(dag, dag_old, NodeType::X_NODE, rp_idx, y_node,
                             traps(right_trap).dag_leaf);
              }
            else
              {
                traps(cur_above).upper_right = old_t.upper_right;
                traps(cur_above).lower_right = old_t.lower_right;
                traps(cur_below).upper_right = old_t.upper_right;
                traps(cur_below).lower_right = old_t.lower_right;
                update_neighbor(traps, old_t.upper_right, ti, cur_above);
                update_neighbor(traps, old_t.lower_right, ti, cur_below);
 
                // Build DAG for this trapezoid.
                const size_t dag_old = old_t.dag_leaf;
                replace_leaf(dag, dag_old, NodeType::Y_NODE, seg_idx, traps(cur_above).dag_leaf,
                             traps(cur_below).dag_leaf);
              }
          }
        else if (is_first)
          {
            // First but not last — build DAG with X-node for left endpoint.
            const size_t dag_old = old_t.dag_leaf;
            const size_t y_node = dag.size();
            dag.append(DagNode{NodeType::Y_NODE, seg_idx, traps(cur_above).dag_leaf,
                               traps(cur_below).dag_leaf});
            if (shared_left)
              replace_leaf(dag, dag_old, NodeType::Y_NODE, seg_idx, traps(cur_above).dag_leaf,
                           traps(cur_below).dag_leaf);
            else
              replace_leaf(dag, dag_old, NodeType::X_NODE, lp_idx, traps(left_trap).dag_leaf, y_node);
          }
        else
          {
            // Middle trapezoid — just a Y-node.
            const size_t dag_old = old_t.dag_leaf;
            replace_leaf(dag, dag_old, NodeType::Y_NODE, seg_idx, traps(cur_above).dag_leaf,
                         traps(cur_below).dag_leaf);
          }
      }
  }
 
public:
  [[nodiscard]] Result operator () (const Array<Segment> &input_segments) const
  {
    Result ret;
    const size_t n = input_segments.size();
    ret.num_input_segments = n;
 
    // Collect unique points from segments.
    // Orient all segments left-to-right (src < tgt lexicographically).
    ret.segments.reserve(n + 2);
    for (size_t i = 0; i < n; ++i)
      {
        const Point &s = input_segments(i).get_src_point();
        const Point &t = input_segments(i).get_tgt_point();
        ah_domain_error_if(s == t) << "Degenerate segment (src == tgt) at index " << i;
        if (s < t)
          ret.segments.append(Segment(s, t));
        else
          ret.segments.append(Segment(t, s));
      }
 
    // Collect and deduplicate points.
    {
      Array<Point> all_pts;
      all_pts.reserve(2 * n);
      for (size_t i = 0; i < n; ++i)
        {
          all_pts.append(ret.segments(i).get_src_point());
          all_pts.append(ret.segments(i).get_tgt_point());
        }
      // Sort lexicographically.
      in_place_sort(all_pts);
      // Deduplicate.
      for (size_t i = 0; i < all_pts.size(); ++i)
        {
          if (ret.points.is_empty() or not (ret.points(ret.points.size() - 1) == all_pts(i)))
            ret.points.append(all_pts(i));
        }
    }
 
    ret.num_input_points = ret.points.size();
 
    // Compute bounding box with margin.
    if (ret.points.is_empty())
      {
        // No input segments: create a trivial bounding box.
        ret.points.append(Point(-1, -1));
        ret.points.append(Point(1, -1));
        ret.points.append(Point(1, 1));
        ret.points.append(Point(-1, 1));
      }
 
    Geom_Number mnx = ret.points(0).get_x();
    Geom_Number mxx = mnx;
    Geom_Number mny = ret.points(0).get_y();
    Geom_Number mxy = mny;
    for (size_t i = 1; i < ret.points.size(); ++i)
      {
        if (ret.points(i).get_x() < mnx)
          mnx = ret.points(i).get_x();
        if (ret.points(i).get_x() > mxx)
          mxx = ret.points(i).get_x();
        if (ret.points(i).get_y() < mny)
          mny = ret.points(i).get_y();
        if (ret.points(i).get_y() > mxy)
          mxy = ret.points(i).get_y();
      }
 
    Geom_Number margin = (mxx - mnx > mxy - mny) ? mxx - mnx : mxy - mny;
    if (margin == 0)
      margin = 1;
    margin = margin + 1;
 
    // Bounding box corner points.
    const Point bl(mnx - margin, mny - margin);
    const Point br(mxx + margin, mny - margin);
    const Point tl(mnx - margin, mxy + margin);
    const Point tr(mxx + margin, mxy + margin);
 
    const size_t bl_idx = ret.points.size();
    ret.points.append(bl);
    ret.points.append(br);
    ret.points.append(tl);
    const size_t tr_idx = ret.points.size();
    ret.points.append(tr);
 
    // Bounding box segments: top (tl→tr) and bottom (bl→br).
    const size_t top_seg = ret.segments.size();
    ret.segments.append(Segment(tl, tr));
    const size_t bot_seg = ret.segments.size();
    ret.segments.append(Segment(bl, br));
 
    // Initialize: one trapezoid spanning the bounding box.
    ret.dag_root = 0;
    const size_t t0 = make_trapezoid(ret.trapezoids, ret.dag, top_seg, bot_seg, bl_idx, tr_idx);
    (void) t0;
 
    // Randomized insertion order.
    if (n == 0)
      return ret;
 
    Array<size_t> order;
    order.reserve(n);
    for (size_t i = 0; i < n; ++i)
      order.append(i);
 
    // Fisher-Yates shuffle.
    {
      std::random_device rd;
      std::mt19937 gen(rd());
      for (size_t i = n - 1; i > 0; --i)
        {
          std::uniform_int_distribution<size_t> dis(0, i);
          const size_t j = dis(gen);
          const size_t tmp = order(i);
          order(i) = order(j);
          order(j) = tmp;
        }
    }
 
    // Insert segments one by one.
    for (size_t oi = 0; oi < n; ++oi)
      {
        const size_t si = order(oi);
        const Segment &seg = ret.segments(si);
 
        // Locate the trapezoid containing the left endpoint.
        const size_t start =
          dag_locate(ret.points, ret.segments, ret.dag, seg.get_src_point(), ret.dag_root);
 
        // Find all trapezoids crossed by this segment.
        Array<size_t> crossed =
          find_crossed_trapezoids(ret.points, ret.segments, ret.trapezoids, si, start);
 
        if (crossed.size() == 1)
          split_single_trapezoid(ret.points, ret.segments, ret.trapezoids, ret.dag, si, crossed(0));
        else
          split_multiple_trapezoids(ret.points, ret.segments, ret.trapezoids, ret.dag, si, crossed);
      }
 
    return ret;
  }
 
  [[nodiscard]] Result operator () (const Polygon &polygon) const
  {
    ah_domain_error_if(not polygon.is_closed()) << "Polygon must be closed";
    ah_domain_error_if(polygon.size() < 3) << "Polygon must have at least 3 vertices";
 
    Array<Segment> segs;
    for (Polygon::Segment_Iterator it(polygon); it.has_curr(); it.next_ne())
      segs.append(it.get_current_segment());
    return (*this)(segs);
  }
 
  [[nodiscard]] Result operator () (const Array<Polygon> &polygons) const
  {
    Array<Segment> segs;
    for (size_t i = 0; i < polygons.size(); ++i)
      {
        const Polygon &poly = polygons(i);
        ah_domain_error_if(not poly.is_closed()) << "Polygon " << i << " must be closed";
        ah_domain_error_if(poly.size() < 3) << "Polygon " << i << " must have at least 3 vertices";
        for (Polygon::Segment_Iterator it(poly); it.has_curr(); it.next_ne())
          segs.append(it.get_current_segment());
      }
    return (*this)(segs);
  }
};
 
// ============================================================================
// GeomNumber Concept (C++20)
// ============================================================================
 
#if __cplusplus >= 202002L
 
#include <concepts>
 
template <typename T>
concept GeomNumberType = requires(T a, T b, int i) {
  { T(i) } -> std::convertible_to<T>;
  { a + b } -> std::convertible_to<T>;
  { a - b } -> std::convertible_to<T>;
  { a * b } -> std::convertible_to<T>;
  { a / b } -> std::convertible_to<T>;
  { a == b } -> std::convertible_to<bool>;
  { a != b } -> std::convertible_to<bool>;
  { a < b } -> std::convertible_to<bool>;
  { a <= b } -> std::convertible_to<bool>;
  { a > b } -> std::convertible_to<bool>;
  { a >= b } -> std::convertible_to<bool>;
  { -a } -> std::convertible_to<T>;
};
 
// Verify that Geom_Number satisfies the concept.
static_assert(GeomNumberType<Geom_Number>, "Geom_Number must satisfy GeomNumberType");
static_assert(GeomNumberType<double>, "double must satisfy GeomNumberType");
static_assert(GeomNumberType<long long>, "long long must satisfy GeomNumberType");
 
#endif  // C++20
}  // namespace Aleph
 
#endif  // GEOM_ALGORITHMS_H