// Copyright (c) 2018 INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v5.5/Shape_detection/include/CGAL/Shape_detection/Region_growing/Region_growing_on_polygon_mesh/One_ring_neighbor_query.h $
// $Id: One_ring_neighbor_query.h 393f547 2020-11-26T14:21:10+01:00 Maxime Gimeno
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Florent Lafarge, Simon Giraudot, Thien Hoang, Dmitry Anisimov
//

#ifndef CGAL_SHAPE_DETECTION_REGION_GROWING_POLYGON_MESH_ONE_RING_NEIGHBOR_QUERY_H
#define CGAL_SHAPE_DETECTION_REGION_GROWING_POLYGON_MESH_ONE_RING_NEIGHBOR_QUERY_H

#include <CGAL/license/Shape_detection.h>

// Boost includes.
#include <boost/graph/properties.hpp>
#include <boost/graph/graph_traits.hpp>

// Face graph includes.
#include <CGAL/boost/graph/iterator.h>
#include <CGAL/boost/graph/graph_traits_Surface_mesh.h>
#include <CGAL/boost/graph/graph_traits_Polyhedron_3.h>

// CGAL includes.
#include <CGAL/assertions.h>

// Internal includes.
#include <CGAL/Shape_detection/Region_growing/internal/property_map.h>

namespace CGAL {
namespace Shape_detection {
namespace Polygon_mesh {

  /*!
    \ingroup PkgShapeDetectionRGOnMesh

    \brief Edge-adjacent faces connectivity in a polygon mesh.

    This class returns all faces, which are edge-adjacent to a query face in a
    polygon mesh being a `PolygonMesh`.

    \tparam PolygonMesh
    must be a model of `FaceListGraph`.

    \tparam FaceRange
    must be a model of `ConstRange` whose iterator type is `RandomAccessIterator` and
    value type is the face type of a polygon mesh.

    \cgalModels `NeighborQuery`
  */
  template<
  typename PolygonMesh,
  typename FaceRange = typename PolygonMesh::Face_range>
  class One_ring_neighbor_query {

  public:

    /// \cond SKIP_IN_MANUAL
    using Face_graph = PolygonMesh;
    using Face_range = FaceRange;

    using Face_to_index_map
    = internal::Item_to_index_property_map<Face_range>;
    /// \endcond

    /// \name Initialization
    /// @{

    /*!
      \brief initializes all internal data structures.

      \param pmesh
      an instance of a `PolygonMesh` that represents a polygon mesh

      \pre `faces(pmesh).size() > 0`
    */
    One_ring_neighbor_query(
      const PolygonMesh& pmesh) :
    m_face_graph(pmesh),
    m_face_range(faces(m_face_graph)),
    m_face_to_index_map(m_face_range) {

      CGAL_precondition(m_face_range.size() > 0);
    }

    /// @}

    /// \name Access
    /// @{

    /*!
      \brief implements `NeighborQuery::operator()()`.

      This operator retrieves indices of all faces,
      which are edge-adjacent to the face with the index `query_index`.
      These indices are returned in `neighbors`.

      \param query_index
      index of the query face

      \param neighbors
      indices of faces, which are neighbors of the query face

      \pre `query_index >= 0 && query_index < faces(pmesh).size()`
    */
    void operator()(
      const std::size_t query_index,
      std::vector<std::size_t>& neighbors) const {

      neighbors.clear();

      CGAL_precondition(query_index < m_face_range.size());

      const auto query_face = *(m_face_range.begin() + query_index);
      const auto query_hedge = halfedge(query_face, m_face_graph);

      const auto faces = faces_around_face(query_hedge, m_face_graph);
      for (const auto face : faces) {
        const std::size_t face_index = get(m_face_to_index_map, face);

        if (face_index != std::size_t(-1)) // not a null face
          neighbors.push_back(face_index);
      }
    }

    /// @}

  private:

    // Fields.
    const Face_graph& m_face_graph;
    const Face_range m_face_range;

    const Face_to_index_map m_face_to_index_map;
  };

} // namespace Polygon_mesh
} // namespace Shape_detection
} // namespace CGAL

#endif // CGAL_SHAPE_DETECTION_REGION_GROWING_POLYGON_MESH_ONE_RING_NEIGHBOR_QUERY_H
