text: // Copyright (c) 2011 CNRS and LIRIS' Establishments (France).
  // All rights reserved.
  //
  // This file is part of CGAL (www.cgal.org)
  //
  // $URL: https://github.com/CGAL/cgal/blob/v5.1/Triangulation_2/include/CGAL/Triangulation_2_to_lcc.h $
  // $Id: Triangulation_2_to_lcc.h 0779373 2020-03-26T13:31:46+01:00 Sébastien Loriot
  // SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
  //
  // Author(s)     : Guillaume Damiand <guillaume.damiand@liris.cnrs.fr>
  //
  
  #ifndef CGAL_TRIANGULATION_2_TO_LCC_H
  #define CGAL_TRIANGULATION_2_TO_LCC_H
  
  #include <CGAL/assertions.h>
  #include <map>
  
  namespace CGAL {
  
    /** Convert a given Triangulation_2 into a 2D linear cell complex.
     * @param alcc the used linear cell complex.
     * @param atr the Triangulation_2.
     * @param aface_to_dart a pointer to a std::map associating to each
     *        triangle of atr a corresponding dart in alcc. Not used if nullptr.
     * @return A dart incident to the infinite vertex.
     */
    template < class LCC, class Triangulation >
    typename LCC::Dart_handle import_from_triangulation_2
    (LCC& alcc, const Triangulation &atr,
     std::map<typename Triangulation::Face_handle,
              typename LCC::Dart_handle >* aface_to_dart=nullptr)
    {
      CGAL_static_assertion( LCC::dimension>=2 && LCC::ambient_dimension==2 );
  
      // Case of empty triangulations.
      if (atr.number_of_vertices()==0) return LCC::null_handle;
  
      // Check the dimension.
      if (atr.dimension()!=2) return LCC::null_handle;
      CGAL_assertion(atr.is_valid());
  
      typedef typename Triangulation::Vertex_handle         TVertex_handle;
      typedef typename Triangulation::All_vertices_iterator TVertex_iterator;
      typedef typename Triangulation::All_faces_iterator    TFace_iterator;
      typedef typename std::map
        < TFace_iterator, typename LCC::Dart_handle >::iterator itmap_tcell;
  
      // Create vertices in the map and associate in a map
      // TVertex_handle and vertices in the map.
      std::map< TVertex_handle, typename LCC::Vertex_attribute_handle > TV;
      for (TVertex_iterator itv = atr.all_vertices_begin();
           itv != atr.all_vertices_end(); ++itv)
      {
        TV[itv] = alcc.create_vertex_attribute(itv->point());
      }
  
      // Create the triangles and create a map to link Cell_iterator
      // and triangles.
      TFace_iterator it;
  
      std::map<typename Triangulation::Face_handle, typename LCC::Dart_handle> TC;
      std::map<typename Triangulation::Face_handle, typename LCC::Dart_handle>*
        mytc = (aface_to_dart==nullptr?&TC:aface_to_dart);
  
      itmap_tcell maptcell_it;
  
      typename LCC::Dart_handle res=LCC::null_handle, dart=LCC::null_handle;
      typename LCC::Dart_handle cur=LCC::null_handle, neighbor=LCC::null_handle;
  
      for (it = atr.all_faces_begin(); it != atr.all_faces_end(); ++it)
      {
        /*     if (it->vertex(0) != atr.infinite_vertex() &&
               it->vertex(1) != atr.infinite_vertex() &&
               it->vertex(2) != atr.infinite_vertex() &&
               it->vertex(3) != atr.infinite_vertex())
        */
        {
          res = alcc.make_triangle(TV[it->vertex(0)],
                                   TV[it->vertex(1)],
                                   TV[it->vertex(2)]);
  
          if ( dart==LCC::null_handle )
          {
            if ( it->vertex(0) == atr.infinite_vertex() )
              dart = res;
            else if ( it->vertex(1) == atr.infinite_vertex() )
              dart = alcc.next(res);
            else if ( it->vertex(2) == atr.infinite_vertex() )
              dart = alcc.previous(res);
          }
  
          for (unsigned int i=0; i<3; ++i)
          {
            switch (i)
            {
            case 0: cur = alcc.next(res); break;
            case 1: cur = alcc.previous(res); break;
            case 2: cur = res; break;
            }
  
            maptcell_it = mytc->find(it->neighbor(i));
            if (maptcell_it != mytc->end())
            {
              switch (atr.mirror_index(it,i) )
              {
              case 0: neighbor = alcc.next(maptcell_it->second);
                break;
              case 1: neighbor = alcc.previous(maptcell_it->second);
                break;
              case 2: neighbor = maptcell_it->second; break;
              }
              alcc.template set_opposite<2>(cur, neighbor);
            }
          }
          (*mytc)[it] = res;
        }
      }
  
      CGAL_assertion(dart!=LCC::null_handle);
      return dart;
    }
  
  } // namespace CGAL
  
  #endif // CGAL_TRIANGULATION_2_TO_LCC_H
  