// 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/v6.2/Shape_detection/include/CGAL/Shape_detection/Region_growing/Polygon_mesh/One_ring_neighbor_query.h $
// $Id: include/CGAL/Shape_detection/Region_growing/Polygon_mesh/One_ring_neighbor_query.h cac3e9d75e2 $
// 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>

#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
  a model of `FaceListGraph`

  \tparam FaceRange
  a model of `ConstRange` whose iterator type is `RandomAccessIterator` and
  value type is the face type of a polygon mesh (`boost::graph_traits<PolygonMesh>::face_descriptor`)

  \cgalModels{NeighborQuery}
*/
template<typename PolygonMesh>
class One_ring_neighbor_query {
  using face_descriptor = typename boost::graph_traits<PolygonMesh>::face_descriptor;
public:
  /// Item type.
  using Item = typename boost::graph_traits<PolygonMesh>::face_descriptor;
  using Region = std::vector<Item>;

  /// \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)
  {}

  /// @}

  /// \name Access
  /// @{

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

    This operator retrieves all faces,
    which are edge-adjacent to the face `query`.
    These `Items` are returned in `neighbors`.

    \param query
    `Item` of the query face

    \param neighbors
    `Items` of faces, which are neighbors of the query face

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

    neighbors.clear();
    const auto query_hedge = halfedge(query, m_face_graph);

    for (face_descriptor face : faces_around_face(query_hedge, m_face_graph))
    {
      if (face != boost::graph_traits<PolygonMesh>::null_face())
      {
        neighbors.push_back(face);
      }
    }
  }

  /// @}

private:
  const PolygonMesh& m_face_graph;
};

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

#endif // CGAL_SHAPE_DETECTION_REGION_GROWING_POLYGON_MESH_ONE_RING_NEIGHBOR_QUERY_H
