// Copyright (c) 2007,2009,2010,2011 Tel-Aviv University (Israel).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.2/Arrangement_on_surface_2/include/CGAL/Arr_topology_traits/Arr_unb_planar_vert_decomp_helper.h $
// $Id: include/CGAL/Arr_topology_traits/Arr_unb_planar_vert_decomp_helper.h cac3e9d75e2 $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s): Ron Wein   <wein@post.tau.ac.il>
//            Efi Fogel  <efif@post.tau.ac.il>

#ifndef CGAL_ARR_UNB_PLANAR_VERT_DECOMP_HELPER_H
#define CGAL_ARR_UNB_PLANAR_VERT_DECOMP_HELPER_H

#include <CGAL/license/Arrangement_on_surface_2.h>

/*! \file
 *
 * Definition of the Arr_unb_planar_vert_decomp_helper class-template.
 */

namespace CGAL {

/*! \class Arr_unb_planar_vert_decomp_helper
 *
 * A helper class for the vertical decomposition sweep-line visitor, suitable
 * for an Arrangement_on_surface_2 instantiated with a topology-traits class
 * for unbounded curves in the plane.
 */
template <typename Traits_, typename Arrangement_, typename Event_,
          typename Subcurve_>
class Arr_unb_planar_vert_decomp_helper {
public:
  typedef Traits_                                       Geometry_traits_2;
  typedef Arrangement_                                  Arrangement_2;
  typedef Event_                                        Event;
  typedef Subcurve_                                     Subcurve;
  typedef typename Subcurve::Allocator                  Allocator;

private:
  typedef Geometry_traits_2                             Gt2;

public:
  typedef typename Arrangement_2::Vertex_const_handle   Vertex_const_handle;
  typedef typename Arrangement_2::Halfedge_const_handle Halfedge_const_handle;
  typedef typename Arrangement_2::Face_const_handle     Face_const_handle;

  typedef std::variant<Vertex_const_handle, Halfedge_const_handle,
                         Face_const_handle>             Cell_type;
  typedef std::optional<Cell_type>                    Vert_type;

protected:
  typedef typename Arrangement_2::Topology_traits       Topology_traits;

  // Data members:
  const Topology_traits* m_top_traits;  // The topology-traits class.
  Halfedge_const_handle m_top_fict;     // The current top fictitious halfedge.
  Halfedge_const_handle m_bottom_fict;  // The current bottom fictitious
                                        // halfedge.

public:
  /*! constructs.
   * \param arr The arrangement.
   */
  Arr_unb_planar_vert_decomp_helper(const Arrangement_2* arr) :
    m_top_traits(arr->topology_traits())
  {}

  /// \name Notification functions.
  //@{

  /* A notification issued before the sweep process starts. */
  void before_sweep();

  /*! A notification invoked after the sweep-line finishes handling the given
   * event.
   */
  void after_handle_event(Event* event);
  //@}

  /*! obtains the current top object. */
  Vert_type top_object() const { return Vert_type(m_top_fict); }

  /*! obtains the current bottom object. */
  Vert_type bottom_object() const { return Vert_type(m_bottom_fict); }
};

//-----------------------------------------------------------------------------
// Member-function definitions:
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
// A notification issued before the sweep process starts.
//
template <typename Tr, typename Arr, typename Event_, typename Subcurve_>
void Arr_unb_planar_vert_decomp_helper<Tr, Arr, Event_, Subcurve_>::
before_sweep()
{
  // Initialize the fictitious halfedge lying on the top edge of the
  // bounding rectangle. We start from the leftmost halfedge, which is
  // incident to the top-left vertex and directed from right to left.
  Vertex_const_handle v_tl =
    Vertex_const_handle(m_top_traits->top_left_vertex());

  m_top_fict = v_tl->incident_halfedges();
  if (m_top_fict->direction() == ARR_LEFT_TO_RIGHT)
    m_top_fict = m_top_fict->next()->twin();

  CGAL_assertion_code (
    Vertex_const_handle v_tr =
      Vertex_const_handle(m_top_traits->top_right_vertex());
  );
  CGAL_assertion
    ((m_top_fict->source() == v_tr) ||
     (m_top_fict->source()->parameter_space_in_x() == ARR_INTERIOR &&
      m_top_fict->source()->parameter_space_in_y() == ARR_TOP_BOUNDARY));

  // Initialize the fictitious halfedge lying on the bottom edge of the
  // bounding rectangle. We start from the leftmost halfedge, which is
  // incident to the bottom-left vertex and whose source is not at -oo.
  Vertex_const_handle  v_bl =
    Vertex_const_handle(m_top_traits->bottom_left_vertex());

  m_bottom_fict = v_bl->incident_halfedges();
  if (m_bottom_fict->source()->parameter_space_in_x() == ARR_LEFT_BOUNDARY)
      m_bottom_fict = m_bottom_fict->next()->twin();

  CGAL_assertion_code(
    Vertex_const_handle  v_br =
      Vertex_const_handle (m_top_traits->bottom_right_vertex());
  );
  CGAL_assertion
    ((m_bottom_fict->source() == v_br) ||
     (m_bottom_fict->source()->parameter_space_in_x() == ARR_INTERIOR &&
      m_bottom_fict->source()->parameter_space_in_y() == ARR_BOTTOM_BOUNDARY));
}

//-----------------------------------------------------------------------------
// A notification invoked after the sweep-line finishes handling the given
// event.
//
template <typename Tr, typename Arr, typename Evnt, typename Sbcv>
void Arr_unb_planar_vert_decomp_helper<Tr, Arr, Evnt, Sbcv>::
after_handle_event(Event* event)
{
  // If the event is at infinity and occurs on the top edge of the fictitious
  // face (namely x is finite and y = +oo), we have to update the fictitious
  // halfedges we keep.
  if (event->is_closed()) return;

  if (event->parameter_space_in_x() != ARR_INTERIOR) return;

  Arr_parameter_space ps_y = event->parameter_space_in_y();

  if (ps_y == ARR_TOP_BOUNDARY) {
    // Update the fictitious top halfedge.
    m_top_fict = m_top_fict->twin()->next()->twin();
  }
  else {
    CGAL_assertion (ps_y == ARR_BOTTOM_BOUNDARY);

    // Update the fictitious bottom halfedge.
    m_bottom_fict = m_bottom_fict->prev();
  }
}

} // namespace CGAL

#endif
