/* -*- mode: C++; indent-tabs-mode: nil; -*-

 *

 * This file is a part of LEMON, a generic C++ optimization library.

 *

 * Copyright (C) 2003-2009

 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

 * (Egervary Research Group on Combinatorial Optimization, EGRES).

 *

 * Permission to use, modify and distribute this software is granted

 * provided that this copyright notice appears in all copies. For

 * precise terms see the accompanying LICENSE file.

 *

 * This software is provided "AS IS" with no warranty of any kind,

 * express or implied, and with no claim as to its suitability for any

 * purpose.

 *

 */

#ifndef LEMON_PLANARITY_H

#define LEMON_PLANARITY_H

/// \ingroup planar

/// \file

/// \brief Planarity checking, embedding, drawing and coloring

#include <vector>

#include <list>

#include <lemon/dfs.h>

#include <lemon/bfs.h>

#include <lemon/radix_sort.h>

#include <lemon/maps.h>

#include <lemon/path.h>

#include <lemon/bucket_heap.h>

#include <lemon/adaptors.h>

#include <lemon/edge_set.h>

#include <lemon/color.h>

#include <lemon/dim2.h>

namespace lemon {

  namespace _planarity_bits {

    template <typename Graph>

    struct PlanarityVisitor : DfsVisitor<Graph> {

      TEMPLATE_GRAPH_TYPEDEFS(Graph);

      typedef typename Graph::template NodeMap<Arc> PredMap;

      typedef typename Graph::template EdgeMap<bool> TreeMap;

      typedef typename Graph::template NodeMap<int> OrderMap;

      typedef std::vector<Node> OrderList;

      typedef typename Graph::template NodeMap<int> LowMap;

      typedef typename Graph::template NodeMap<int> AncestorMap;

      PlanarityVisitor(const Graph& graph,

                       PredMap& pred_map, TreeMap& tree_map,

                       OrderMap& order_map, OrderList& order_list,

                       AncestorMap& ancestor_map, LowMap& low_map)

        : _graph(graph), _pred_map(pred_map), _tree_map(tree_map),

          _order_map(order_map), _order_list(order_list),

          _ancestor_map(ancestor_map), _low_map(low_map) {}

      void reach(const Node& node) {

        _order_map[node] = _order_list.size();

        _low_map[node] = _order_list.size();

        _ancestor_map[node] = _order_list.size();

        _order_list.push_back(node);

      }

      void discover(const Arc& arc) {

        Node source = _graph.source(arc);

        Node target = _graph.target(arc);

        _tree_map[arc] = true;

        _pred_map[target] = arc;

      }

      void examine(const Arc& arc) {

        Node source = _graph.source(arc);

        Node target = _graph.target(arc);

        if (_order_map[target] < _order_map[source] && !_tree_map[arc]) {

          if (_low_map[source] > _order_map[target]) {

            _low_map[source] = _order_map[target];

          }

          if (_ancestor_map[source] > _order_map[target]) {

            _ancestor_map[source] = _order_map[target];

          }

        }

      }

      void backtrack(const Arc& arc) {

        Node source = _graph.source(arc);

        Node target = _graph.target(arc);

        if (_low_map[source] > _low_map[target]) {

          _low_map[source] = _low_map[target];

        }

      }

      const Graph& _graph;

      PredMap& _pred_map;

      TreeMap& _tree_map;

      OrderMap& _order_map;

      OrderList& _order_list;

      AncestorMap& _ancestor_map;

      LowMap& _low_map;

    };

    template <typename Graph, bool embedding = true>

    struct NodeDataNode {

      int prev, next;

      int visited;

      typename Graph::Arc first;

      bool inverted;

    };

    template <typename Graph>

    struct NodeDataNode<Graph, false> {

      int prev, next;

      int visited;

    };

    template <typename Graph>

    struct ChildListNode {

      typedef typename Graph::Node Node;

      Node first;

      Node prev, next;

    };

    template <typename Graph>

    struct ArcListNode {

      typename Graph::Arc prev, next;

    };

    template <typename Graph>

    class PlanarityChecking {

    private:

      TEMPLATE_GRAPH_TYPEDEFS(Graph);

      const Graph& _graph;

    private:

      typedef typename Graph::template NodeMap<Arc> PredMap;

      typedef typename Graph::template EdgeMap<bool> TreeMap;

      typedef typename Graph::template NodeMap<int> OrderMap;

      typedef std::vector<Node> OrderList;

      typedef typename Graph::template NodeMap<int> LowMap;

      typedef typename Graph::template NodeMap<int> AncestorMap;

      typedef _planarity_bits::NodeDataNode<Graph> NodeDataNode;

      typedef std::vector<NodeDataNode> NodeData;

      typedef _planarity_bits::ChildListNode<Graph> ChildListNode;

      typedef typename Graph::template NodeMap<ChildListNode> ChildLists;

      typedef typename Graph::template NodeMap<std::list<int> > MergeRoots;

      typedef typename Graph::template NodeMap<bool> EmbedArc;

    public:

      PlanarityChecking(const Graph& graph) : _graph(graph) {}

      bool run() {

        typedef _planarity_bits::PlanarityVisitor<Graph> Visitor;

        PredMap pred_map(_graph, INVALID);

        TreeMap tree_map(_graph, false);

        OrderMap order_map(_graph, -1);

        OrderList order_list;

        AncestorMap ancestor_map(_graph, -1);

        LowMap low_map(_graph, -1);

        Visitor visitor(_graph, pred_map, tree_map,

                        order_map, order_list, ancestor_map, low_map);

        DfsVisit<Graph, Visitor> visit(_graph, visitor);

        visit.run();

        ChildLists child_lists(_graph);

        createChildLists(tree_map, order_map, low_map, child_lists);

        NodeData node_data(2 * order_list.size());

        EmbedArc embed_arc(_graph, false);

        MergeRoots merge_roots(_graph);

        for (int i = order_list.size() - 1; i >= 0; --i) {

          Node node = order_list[i];

          Node source = node;

          for (OutArcIt e(_graph, node); e != INVALID; ++e) {

            Node target = _graph.target(e);

            if (order_map[source] < order_map[target] && tree_map[e]) {

              initFace(target, node_data, order_map, order_list);

            }

          }

          for (OutArcIt e(_graph, node); e != INVALID; ++e) {

            Node target = _graph.target(e);

            if (order_map[source] < order_map[target] && !tree_map[e]) {

              embed_arc[target] = true;

              walkUp(target, source, i, pred_map, low_map,

                     order_map, order_list, node_data, merge_roots);

            }

          }

          for (typename MergeRoots::Value::iterator it =

                 merge_roots[node].begin(); 

               it != merge_roots[node].end(); ++it) {

            int rn = *it;

            walkDown(rn, i, node_data, order_list, child_lists,

                     ancestor_map, low_map, embed_arc, merge_roots);

          }

          merge_roots[node].clear();

          for (OutArcIt e(_graph, node); e != INVALID; ++e) {

            Node target = _graph.target(e);

            if (order_map[source] < order_map[target] && !tree_map[e]) {

              if (embed_arc[target]) {

                return false;

              }

            }

          }

        }

        return true;

      }

    private:

      void createChildLists(const TreeMap& tree_map, const OrderMap& order_map,

                            const LowMap& low_map, ChildLists& child_lists) {

        for (NodeIt n(_graph); n != INVALID; ++n) {

          Node source = n;

          std::vector<Node> targets;

          for (OutArcIt e(_graph, n); e != INVALID; ++e) {

            Node target = _graph.target(e);

            if (order_map[source] < order_map[target] && tree_map[e]) {

              targets.push_back(target);

            }

          }

          if (targets.size() == 0) {

            child_lists[source].first = INVALID;

          } else if (targets.size() == 1) {

            child_lists[source].first = targets[0];

            child_lists[targets[0]].prev = INVALID;

            child_lists[targets[0]].next = INVALID;

          } else {

            radixSort(targets.begin(), targets.end(), mapToFunctor(low_map));

            for (int i = 1; i < int(targets.size()); ++i) {

              child_lists[targets[i]].prev = targets[i - 1];

              child_lists[targets[i - 1]].next = targets[i];

            }

            child_lists[targets.back()].next = INVALID;

            child_lists[targets.front()].prev = INVALID;

            child_lists[source].first = targets.front();

          }

        }

      }

      void walkUp(const Node& node, Node root, int rorder,

                  const PredMap& pred_map, const LowMap& low_map,

                  const OrderMap& order_map, const OrderList& order_list,

                  NodeData& node_data, MergeRoots& merge_roots) {

        int na, nb;

        bool da, db;

        na = nb = order_map[node];

        da = true; db = false;

        while (true) {

          if (node_data[na].visited == rorder) break;

          if (node_data[nb].visited == rorder) break;

          node_data[na].visited = rorder;

          node_data[nb].visited = rorder;

          int rn = -1;

          if (na >= int(order_list.size())) {

            rn = na;

          } else if (nb >= int(order_list.size())) {

            rn = nb;

          }

          if (rn == -1) {

            int nn;

            nn = da ? node_data[na].prev : node_data[na].next;

            da = node_data[nn].prev != na;

            na = nn;

            nn = db ? node_data[nb].prev : node_data[nb].next;

            db = node_data[nn].prev != nb;

            nb = nn;

          } else {

            Node rep = order_list[rn - order_list.size()];

            Node parent = _graph.source(pred_map[rep]);

            if (low_map[rep] < rorder) {

              merge_roots[parent].push_back(rn);

            } else {

              merge_roots[parent].push_front(rn);

            }

            if (parent != root) {

              na = nb = order_map[parent];

              da = true; db = false;

            } else {

              break;

            }

          }

        }

      }

      void walkDown(int rn, int rorder, NodeData& node_data,

                    OrderList& order_list, ChildLists& child_lists,

                    AncestorMap& ancestor_map, LowMap& low_map,

                    EmbedArc& embed_arc, MergeRoots& merge_roots) {

        std::vector<std::pair<int, bool> > merge_stack;

        for (int di = 0; di < 2; ++di) {

          bool rd = di == 0;

          int pn = rn;

          int n = rd ? node_data[rn].next : node_data[rn].prev;

          while (n != rn) {

            Node node = order_list[n];

            if (embed_arc[node]) {

              // Merging components on the critical path

              while (!merge_stack.empty()) {

                // Component root

                int cn = merge_stack.back().first;

                bool cd = merge_stack.back().second;

                merge_stack.pop_back();

                // Parent of component

                int dn = merge_stack.back().first;

                bool dd = merge_stack.back().second;

                merge_stack.pop_back();

                Node parent = order_list[dn];

                // Erasing from merge_roots

                merge_roots[parent].pop_front();

                Node child = order_list[cn - order_list.size()];

                // Erasing from child_lists

                if (child_lists[child].prev != INVALID) {

                  child_lists[child_lists[child].prev].next =

                    child_lists[child].next;

                } else {

                  child_lists[parent].first = child_lists[child].next;

                }

                if (child_lists[child].next != INVALID) {

                  child_lists[child_lists[child].next].prev =

                    child_lists[child].prev;

                }

                // Merging external faces

                {

                  int en = cn;

                  cn = cd ? node_data[cn].prev : node_data[cn].next;

                  cd = node_data[cn].next == en;

                }

                if (cd) node_data[cn].next = dn; else node_data[cn].prev = dn;

                if (dd) node_data[dn].prev = cn; else node_data[dn].next = cn;

              }

              bool d = pn == node_data[n].prev;

              if (node_data[n].prev == node_data[n].next &&

                  node_data[n].inverted) {

                d = !d;

              }

              // Embedding arc into external face

              if (rd) node_data[rn].next = n; else node_data[rn].prev = n;

              if (d) node_data[n].prev = rn; else node_data[n].next = rn;

              pn = rn;

              embed_arc[order_list[n]] = false;

            }

            if (!merge_roots[node].empty()) {

              bool d = pn == node_data[n].prev;

              merge_stack.push_back(std::make_pair(n, d));

              int rn = merge_roots[node].front();

              int xn = node_data[rn].next;

              Node xnode = order_list[xn];

              int yn = node_data[rn].prev;

              Node ynode = order_list[yn];

              bool rd;

              if (!external(xnode, rorder, child_lists, 

                            ancestor_map, low_map)) {

                rd = true;

              } else if (!external(ynode, rorder, child_lists,

                                   ancestor_map, low_map)) {

                rd = false;

              } else if (pertinent(xnode, embed_arc, merge_roots)) {

                rd = true;

              } else {

                rd = false;

              }

              merge_stack.push_back(std::make_pair(rn, rd));

              pn = rn;

              n = rd ? xn : yn;

            } else if (!external(node, rorder, child_lists,

                                 ancestor_map, low_map)) {

              int nn = (node_data[n].next != pn ?

                        node_data[n].next : node_data[n].prev);

              bool nd = n == node_data[nn].prev;

              if (nd) node_data[nn].prev = pn;

              else node_data[nn].next = pn;

              if (n == node_data[pn].prev) node_data[pn].prev = nn;

              else node_data[pn].next = nn;

              node_data[nn].inverted =

                (node_data[nn].prev == node_data[nn].next && nd != rd);

              n = nn;

            }

            else break;

          }

          if (!merge_stack.empty() || n == rn) {

            break;

          }

        }

      }

      void initFace(const Node& node, NodeData& node_data,

                    const OrderMap& order_map, const OrderList& order_list) {

        int n = order_map[node];

        int rn = n + order_list.size();

        node_data[n].next = node_data[n].prev = rn;

        node_data[rn].next = node_data[rn].prev = n;

        node_data[n].visited = order_list.size();

        node_data[rn].visited = order_list.size();

      }

      bool external(const Node& node, int rorder,

                    ChildLists& child_lists, AncestorMap& ancestor_map,

                    LowMap& low_map) {

        Node child = child_lists[node].first;

        if (child != INVALID) {

          if (low_map[child] < rorder) return true;

        }

        if (ancestor_map[node] < rorder) return true;

        return false;

      }

      bool pertinent(const Node& node, const EmbedArc& embed_arc,

                     const MergeRoots& merge_roots) {

        return !merge_roots[node].empty() || embed_arc[node];

      }

    };

  }

  /// \ingroup planar

  ///

  /// \brief Planarity checking of an undirected simple graph

  ///

  /// This function implements the Boyer-Myrvold algorithm for

  /// planarity checking of an undirected graph. It is a simplified

  /// version of the PlanarEmbedding algorithm class because neither

  /// the embedding nor the kuratowski subdivisons are not computed.

  template <typename GR>

  bool checkPlanarity(const GR& graph) {

    _planarity_bits::PlanarityChecking<GR> pc(graph);

    return pc.run();

  }

  /// \ingroup planar

  ///

  /// \brief Planar embedding of an undirected simple graph

  ///

  /// This class implements the Boyer-Myrvold algorithm for planar

  /// embedding of an undirected graph. The planar embedding is an

  /// ordering of the outgoing edges of the nodes, which is a possible

  /// configuration to draw the graph in the plane. If there is not

  /// such ordering then the graph contains a \f$ K_5 \f$ (full graph

  /// with 5 nodes) or a \f$ K_{3,3} \f$ (complete bipartite graph on

  /// 3 ANode and 3 BNode) subdivision.

  ///

  /// The current implementation calculates either an embedding or a

  /// Kuratowski subdivision. The running time of the algorithm is 

  /// \f$ O(n) \f$.

  template <typename Graph>

  class PlanarEmbedding {

  private:

    TEMPLATE_GRAPH_TYPEDEFS(Graph);

    const Graph& _graph;

    typename Graph::template ArcMap<Arc> _embedding;

    typename Graph::template EdgeMap<bool> _kuratowski;

  private:

    typedef typename Graph::template NodeMap<Arc> PredMap;

    typedef typename Graph::template EdgeMap<bool> TreeMap;

    typedef typename Graph::template NodeMap<int> OrderMap;

    typedef std::vector<Node> OrderList;

    typedef typename Graph::template NodeMap<int> LowMap;

    typedef typename Graph::template NodeMap<int> AncestorMap;

    typedef _planarity_bits::NodeDataNode<Graph> NodeDataNode;

    typedef std::vector<NodeDataNode> NodeData;

    typedef _planarity_bits::ChildListNode<Graph> ChildListNode;

    typedef typename Graph::template NodeMap<ChildListNode> ChildLists;

    typedef typename Graph::template NodeMap<std::list<int> > MergeRoots;

    typedef typename Graph::template NodeMap<Arc> EmbedArc;

    typedef _planarity_bits::ArcListNode<Graph> ArcListNode;

    typedef typename Graph::template ArcMap<ArcListNode> ArcLists;

    typedef typename Graph::template NodeMap<bool> FlipMap;

    typedef typename Graph::template NodeMap<int> TypeMap;

    enum IsolatorNodeType {

      HIGHX = 6, LOWX = 7,

      HIGHY = 8, LOWY = 9,

      ROOT = 10, PERTINENT = 11,

      INTERNAL = 12

    };

  public:

    /// \brief The map for store of embedding

    typedef typename Graph::template ArcMap<Arc> EmbeddingMap;

    /// \brief Constructor

    ///

    /// \note The graph should be simple, i.e. parallel and loop arc

    /// free.

    PlanarEmbedding(const Graph& graph)

      : _graph(graph), _embedding(_graph), _kuratowski(graph, false) {}

    /// \brief Runs the algorithm.

    ///

    /// Runs the algorithm.

    /// \param kuratowski If the parameter is false, then the

    /// algorithm does not compute a Kuratowski subdivision.

    ///\return %True when the graph is planar.

    bool run(bool kuratowski = true) {

      typedef _planarity_bits::PlanarityVisitor<Graph> Visitor;

      PredMap pred_map(_graph, INVALID);

      TreeMap tree_map(_graph, false);

      OrderMap order_map(_graph, -1);

      OrderList order_list;

      AncestorMap ancestor_map(_graph, -1);

      LowMap low_map(_graph, -1);

      Visitor visitor(_graph, pred_map, tree_map,

                      order_map, order_list, ancestor_map, low_map);

      DfsVisit<Graph, Visitor> visit(_graph, visitor);

      visit.run();

      ChildLists child_lists(_graph);

      createChildLists(tree_map, order_map, low_map, child_lists);

      NodeData node_data(2 * order_list.size());

      EmbedArc embed_arc(_graph, INVALID);

      MergeRoots merge_roots(_graph);

      ArcLists arc_lists(_graph);

      FlipMap flip_map(_graph, false);

      for (int i = order_list.size() - 1; i >= 0; --i) {

        Node node = order_list[i];

        node_data[i].first = INVALID;

        Node source = node;

        for (OutArcIt e(_graph, node); e != INVALID; ++e) {

          Node target = _graph.target(e);

          if (order_map[source] < order_map[target] && tree_map[e]) {

            initFace(target, arc_lists, node_data,

                     pred_map, order_map, order_list);

          }

        }

        for (OutArcIt e(_graph, node); e != INVALID; ++e) {

          Node target = _graph.target(e);

          if (order_map[source] < order_map[target] && !tree_map[e]) {

            embed_arc[target] = e;

            walkUp(target, source, i, pred_map, low_map,

                   order_map, order_list, node_data, merge_roots);

          }

        }

        for (typename MergeRoots::Value::iterator it =

               merge_roots[node].begin(); it != merge_roots[node].end(); ++it) {

          int rn = *it;

          walkDown(rn, i, node_data, arc_lists, flip_map, order_list,

                   child_lists, ancestor_map, low_map, embed_arc, merge_roots);

        }

        merge_roots[node].clear();

        for (OutArcIt e(_graph, node); e != INVALID; ++e) {

          Node target = _graph.target(e);

          if (order_map[source] < order_map[target] && !tree_map[e]) {

            if (embed_arc[target] != INVALID) {

              if (kuratowski) {

                isolateKuratowski(e, node_data, arc_lists, flip_map,

                                  order_map, order_list, pred_map, child_lists,

                                  ancestor_map, low_map,

                                  embed_arc, merge_roots);

              }

              return false;

            }

          }

        }

      }

      for (int i = 0; i < int(order_list.size()); ++i) {

        mergeRemainingFaces(order_list[i], node_data, order_list, order_map,

                            child_lists, arc_lists);

        storeEmbedding(order_list[i], node_data, order_map, pred_map,

                       arc_lists, flip_map);

      }

      return true;

    }

    /// \brief Gives back the successor of an arc

    ///

    /// Gives back the successor of an arc. This function makes

    /// possible to query the cyclic order of the outgoing arcs from

    /// a node.

    Arc next(const Arc& arc) const {

      return _embedding[arc];

    }

    /// \brief Gives back the calculated embedding map

    ///

    /// The returned map contains the successor of each arc in the

    /// graph.

    const EmbeddingMap& embeddingMap() const {

      return _embedding;

    }

    /// \brief Gives back true if the undirected arc is in the

    /// kuratowski subdivision

    ///

    /// Gives back true if the undirected arc is in the kuratowski

    /// subdivision

    /// \note The \c run() had to be called with true value.

    bool kuratowski(const Edge& edge) {

      return _kuratowski[edge];

    }

  private:

    void createChildLists(const TreeMap& tree_map, const OrderMap& order_map,

                          const LowMap& low_map, ChildLists& child_lists) {

      for (NodeIt n(_graph); n != INVALID; ++n) {

        Node source = n;

        std::vector<Node> targets;

        for (OutArcIt e(_graph, n); e != INVALID; ++e) {

          Node target = _graph.target(e);

          if (order_map[source] < order_map[target] && tree_map[e]) {

            targets.push_back(target);

          }

        }

        if (targets.size() == 0) {

          child_lists[source].first = INVALID;

        } else if (targets.size() == 1) {

          child_lists[source].first = targets[0];

          child_lists[targets[0]].prev = INVALID;

          child_lists[targets[0]].next = INVALID;

        } else {

          radixSort(targets.begin(), targets.end(), mapToFunctor(low_map));

          for (int i = 1; i < int(targets.size()); ++i) {

            child_lists[targets[i]].prev = targets[i - 1];

            child_lists[targets[i - 1]].next = targets[i];

          }

          child_lists[targets.back()].next = INVALID;

          child_lists[targets.front()].prev = INVALID;

          child_lists[source].first = targets.front();

        }

      }

    }

    void walkUp(const Node& node, Node root, int rorder,

                const PredMap& pred_map, const LowMap& low_map,

                const OrderMap& order_map, const OrderList& order_list,

                NodeData& node_data, MergeRoots& merge_roots) {

      int na, nb;

      bool da, db;

      na = nb = order_map[node];

      da = true; db = false;

      while (true) {

        if (node_data[na].visited == rorder) break;

        if (node_data[nb].visited == rorder) break;

        node_data[na].visited = rorder;

        node_data[nb].visited = rorder;

        int rn = -1;

        if (na >= int(order_list.size())) {

          rn = na;

        } else if (nb >= int(order_list.size())) {

          rn = nb;

        }

        if (rn == -1) {

          int nn;

          nn = da ? node_data[na].prev : node_data[na].next;

          da = node_data[nn].prev != na;

          na = nn;

          nn = db ? node_data[nb].prev : node_data[nb].next;

          db = node_data[nn].prev != nb;

          nb = nn;

        } else {

          Node rep = order_list[rn - order_list.size()];

          Node parent = _graph.source(pred_map[rep]);

          if (low_map[rep] < rorder) {

            merge_roots[parent].push_back(rn);

          } else {

            merge_roots[parent].push_front(rn);

          }

          if (parent != root) {

            na = nb = order_map[parent];

            da = true; db = false;

          } else {

            break;

          }

        }

      }

    }

    void walkDown(int rn, int rorder, NodeData& node_data,

                  ArcLists& arc_lists, FlipMap& flip_map,

                  OrderList& order_list, ChildLists& child_lists,

                  AncestorMap& ancestor_map, LowMap& low_map,

                  EmbedArc& embed_arc, MergeRoots& merge_roots) {

      std::vector<std::pair<int, bool> > merge_stack;

      for (int di = 0; di < 2; ++di) {

        bool rd = di == 0;

        int pn = rn;

        int n = rd ? node_data[rn].next : node_data[rn].prev;

        while (n != rn) {

          Node node = order_list[n];

          if (embed_arc[node] != INVALID) {

            // Merging components on the critical path

            while (!merge_stack.empty()) {

              // Component root

              int cn = merge_stack.back().first;

              bool cd = merge_stack.back().second;

              merge_stack.pop_back();

              // Parent of component

              int dn = merge_stack.back().first;

              bool dd = merge_stack.back().second;

              merge_stack.pop_back();

              Node parent = order_list[dn];

              // Erasing from merge_roots

              merge_roots[parent].pop_front();

              Node child = order_list[cn - order_list.size()];

              // Erasing from child_lists

              if (child_lists[child].prev != INVALID) {

                child_lists[child_lists[child].prev].next =

                  child_lists[child].next;

              } else {

                child_lists[parent].first = child_lists[child].next;

              }

              if (child_lists[child].next != INVALID) {

                child_lists[child_lists[child].next].prev =

                  child_lists[child].prev;

              }

              // Merging arcs + flipping

              Arc de = node_data[dn].first;

              Arc ce = node_data[cn].first;

              flip_map[order_list[cn - order_list.size()]] = cd != dd;

              if (cd != dd) {

                std::swap(arc_lists[ce].prev, arc_lists[ce].next);

                ce = arc_lists[ce].prev;

                std::swap(arc_lists[ce].prev, arc_lists[ce].next);

              }

              {

                Arc dne = arc_lists[de].next;

                Arc cne = arc_lists[ce].next;

                arc_lists[de].next = cne;

                arc_lists[ce].next = dne;

                arc_lists[dne].prev = ce;

                arc_lists[cne].prev = de;

              }

              if (dd) {

                node_data[dn].first = ce;

              }

              // Merging external faces

              {

                int en = cn;

                cn = cd ? node_data[cn].prev : node_data[cn].next;

                cd = node_data[cn].next == en;

                 if (node_data[cn].prev == node_data[cn].next &&

                    node_data[cn].inverted) {

                   cd = !cd;

                 }

              }

              if (cd) node_data[cn].next = dn; else node_data[cn].prev = dn;

              if (dd) node_data[dn].prev = cn; else node_data[dn].next = cn;

            }

            bool d = pn == node_data[n].prev;

            if (node_data[n].prev == node_data[n].next &&

                node_data[n].inverted) {

              d = !d;

            }

            // Add new arc

            {

              Arc arc = embed_arc[node];

              Arc re = node_data[rn].first;

              arc_lists[arc_lists[re].next].prev = arc;

              arc_lists[arc].next = arc_lists[re].next;

              arc_lists[arc].prev = re;

              arc_lists[re].next = arc;

              if (!rd) {

                node_data[rn].first = arc;

              }

              Arc rev = _graph.oppositeArc(arc);

              Arc e = node_data[n].first;

              arc_lists[arc_lists[e].next].prev = rev;

              arc_lists[rev].next = arc_lists[e].next;

              arc_lists[rev].prev = e;

              arc_lists[e].next = rev;

              if (d) {

                node_data[n].first = rev;

              }

            }

            // Embedding arc into external face

            if (rd) node_data[rn].next = n; else node_data[rn].prev = n;

            if (d) node_data[n].prev = rn; else node_data[n].next = rn;

            pn = rn;

            embed_arc[order_list[n]] = INVALID;

          }

          if (!merge_roots[node].empty()) {

            bool d = pn == node_data[n].prev;

            if (node_data[n].prev == node_data[n].next &&

                node_data[n].inverted) {

              d = !d;

            }

            merge_stack.push_back(std::make_pair(n, d));

            int rn = merge_roots[node].front();

            int xn = node_data[rn].next;

            Node xnode = order_list[xn];

            int yn = node_data[rn].prev;

            Node ynode = order_list[yn];

            bool rd;

            if (!external(xnode, rorder, child_lists, ancestor_map, low_map)) {

              rd = true;

            } else if (!external(ynode, rorder, child_lists,

                                 ancestor_map, low_map)) {

              rd = false;

            } else if (pertinent(xnode, embed_arc, merge_roots)) {

              rd = true;

            } else {

              rd = false;

            }

            merge_stack.push_back(std::make_pair(rn, rd));