// Copyright (c) 2006  Tel-Aviv University (Israel).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.0.1/Minkowski_sum_2/include/CGAL/Minkowski_sum_2/Union_of_cycles_2.h $
// $Id: include/CGAL/Minkowski_sum_2/Union_of_cycles_2.h 50cfbde3b84 $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Ron Wein   <wein_r@yahoo.com>

#ifndef CGAL_UNION_OF_CYCLES_2_H
#define CGAL_UNION_OF_CYCLES_2_H

#include <CGAL/license/Minkowski_sum_2.h>


#include <CGAL/Arr_extended_dcel.h>
#include <CGAL/Arrangement_2.h>

namespace CGAL {

/*! \class
 * An auxiliary base class for computing the union of the interiors of cycles
 * of x-monotone curves.
 */
template <class Traits_>
class Union_of_cycles_2
{
public:

  typedef Traits_                                        Traits_2;

protected:

  // Traits types:
  typedef typename Traits_2::Point_2                     Point_2;
  typedef typename Traits_2::X_monotone_curve_2          X_monotone_curve_2;

  // Arrangement-related types:
  typedef Arr_face_extended_dcel<Traits_2, int>          Dcel;
  typedef CGAL::Arrangement_2<Traits_2, Dcel>            Arrangement_2;
  typedef typename Arrangement_2::Vertex_handle          Vertex_handle;
  typedef typename Arrangement_2::Halfedge_handle        Halfedge_handle;
  typedef typename Arrangement_2::Face_handle            Face_handle;
  typedef typename Arrangement_2::Vertex_iterator        Vertex_iterator;
  typedef typename Arrangement_2::Edge_iterator          Edge_iterator;
  typedef typename Arrangement_2::Halfedge_iterator      Halfedge_iterator;
  typedef typename Arrangement_2::Face_iterator          Face_iterator;
  typedef typename Arrangement_2::Inner_ccb_iterator     Inner_ccb_iterator;
  typedef typename Arrangement_2::Halfedge_around_vertex_circulator
                                             Halfedge_around_vertex_circulator;
  typedef typename Arrangement_2::Ccb_halfedge_circulator
                                                       Ccb_halfedge_circulator;
  // Data members:
  int                    UNVISITED;    // A code marking unvisited faces.

public:

  /*! Default constructor. */
  Union_of_cycles_2 () :
    UNVISITED (-1000000)
  {}

protected:

  /*!
   * Construct the arrnagement representing the union of the curve cycles,
   * such that every arrangement face is associated with its winding number
   * with respect to the cycles.
   * \param begin An iterator for the first curve in the range.
   * \param end A past-the-end iterator for the curve range.
   * \param arr Output: The arrangement of the curve cycles, where each face
   *                    is associated with its winding number.
   */
  template <class InputIterator>
  void _construct_arrangement (InputIterator begin, InputIterator end,
                               Arrangement_2& arr) const
  {
    CGAL_precondition (arr.is_empty());

    // Construct the arrangement of the curves.
    CGAL::insert (arr, begin, end);

    // Go over all faces and mark them as unvisited, by setting their inside
    // count to UNVISITED.
    Face_iterator                    fit;

    for (fit = arr.faces_begin(); fit != arr.faces_end(); ++fit)
      fit->set_data (UNVISITED);

    // Mark the inside count of the unbounded face as 0, and start a
    // breadth-first search from this face, going over the inner boundary of
    // the single hole (inner CCB) in the unbounded face.
    const Face_handle                uf = arr.unbounded_face();
    Face_handle                      f_next;
    int                              next_count;
    Inner_ccb_iterator               iccb_it = uf->inner_ccbs_begin();
    Ccb_halfedge_circulator          first, circ;
    Halfedge_handle                  he;
    std::list<Face_handle>           queue;

    uf->set_data (0);
    circ = first = *iccb_it;
    do
    {
      he = circ;
      f_next = he->twin()->face();

      if (f_next->data() == UNVISITED)
      {
        next_count = _boundary_count (he->twin());
        f_next->set_data (next_count);
        queue.push_back (f_next);
      }
      else
      {
        CGAL_assertion (f_next->data() == _boundary_count (he->twin()));
      }

      ++circ;

    } while (circ != first);

    ++iccb_it;

    // Make sure that there is a single hole in the unbounded face.
    CGAL_assertion (iccb_it == uf->inner_ccbs_end());

    // The main breadth-first search loop.
    Face_handle                      f_curr;
    int                              curr_count;

    while (! queue.empty())
    {
      f_curr = queue.front();
      curr_count = f_curr->data();
      queue.pop_front();

      // Go over the outer boundary of the current face to visit its edjacent
      // faces.
      circ = first = f_curr->outer_ccb();
      do
      {
        he = circ;
        f_next = he->twin()->face();

        if (f_next->data() == UNVISITED)
        {
          next_count = curr_count + _boundary_count (he->twin());
          f_next->set_data (next_count);
          queue.push_back (f_next);
        }
        else if (f_curr != f_next)
        {
          CGAL_assertion (f_next->data() ==
                          curr_count + _boundary_count (he->twin()));
        }
        ++circ;

      } while (circ != first);

      // Go over the holes (inner CCBs) of the current face.
      for (iccb_it = f_curr->inner_ccbs_begin();
           iccb_it != f_curr->inner_ccbs_end();
           ++iccb_it)
      {
        circ = first = *iccb_it;
        do
        {
          he = circ;
          f_next = he->twin()->face();

          if (f_next->data() == UNVISITED)
          {
            next_count = curr_count + _boundary_count (he->twin());
            f_next->set_data (next_count);
            queue.push_back (f_next);
          }
          else if (f_curr != f_next)
          {
            CGAL_assertion (f_next->data() ==
                            curr_count + _boundary_count (he->twin()));
          }
          ++circ;

        } while (circ != first);
      }
    }

    return;
  }

private:

  /*!
   * Compute the boundary count of the given halfedge, namely the number of
   * curves going in the halfedges direction minus the number of associated
   * curves going in the opposite direction.
   */
  int _boundary_count (Halfedge_handle he) const
  {
    if ((Arr_halfedge_direction) he->direction() == ARR_LEFT_TO_RIGHT)
    {
      // Halfedge is directed from left to right:
      return (he->curve().label().right_count() -
              he->curve().label().left_count());
    }
    else
    {
      // Halfedge is directed from right to left:
      return (he->curve().label().left_count() -
              he->curve().label().right_count());
    }
  }

};

} //namespace CGAL

#endif

