/* This file is part of the Gudhi Library. The Gudhi library 
 *    (Geometric Understanding in Higher Dimensions) is a generic C++ 
 *    library for computational topology.
 *
 *    Author(s):       David Salinas
 *
 *    Copyright (C) 2014  INRIA Sophia Antipolis-Mediterranee (France)
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation, either version 3 of the License, or
 *    (at your option) any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * 
 */

#ifndef UTILS_VERTEX_COLLAPSOR_H_
#define UTILS_VERTEX_COLLAPSOR_H_

#include <list>

#include "utils/Edge_contractor.h"
#include "utils/Furthest_point_epsilon_net.h"
#include "utils/UI_utils.h"

/**
 * Iteratively puts every vertex at the center of its neighbors
 */
template<typename SkBlComplex> class Vertex_collapsor {
 private:
  SkBlComplex& complex_;
  size_t num_collapses_;

 public:
  typedef typename SkBlComplex::Vertex_handle Vertex_handle;
  typedef typename SkBlComplex::Edge_handle Edge_handle;

  /**
   * @brief Modify complex to be the expansion of the k-nearest neighbor
   * symetric graph.
   */
  Vertex_collapsor(SkBlComplex& complex, size_t num_collapses) :
      complex_(complex), num_collapses_(num_collapses) {
    // std::list<Vertex_handle> vertices;
    // vertices.insert(vertices.begin(),complex_.vertex_range().begin(),complex_.vertex_range().end());
    // UIDBG("Collapse vertices");
    // collapse_vertices(vertices);

    std::list<Vertex_handle> vertices;

    UIDBG("Compute eps net");
    Furthest_point_epsilon_net<Complex> eps_net(complex_);

    for (auto vh : eps_net.net_filtration_)
      vertices.push_back(vh.vertex_handle);

    UIDBG("Collapse vertices");
    collapse_vertices(vertices);
  }

 private:
  void collapse_vertices(std::list<Vertex_handle>& vertices) {
    while (!vertices.empty() && num_collapses_--) {
      Vertex_handle current_vertex = vertices.front();
      vertices.pop_front();
      if (is_link_reducible(current_vertex))
        complex_.remove_vertex(current_vertex);
    }
  }

  bool is_link_reducible(Vertex_handle v) {
    auto link = complex_.link(v);
    if (link.empty()) return false;
    if (link.is_cone()) return true;
    if (link.num_connected_components() > 1) return false;
    Edge_contractor<Complex> contractor(link, link.num_vertices() - 1);
    (void)contractor;
    return (link.num_vertices() == 1);
  }
};

#endif  // UTILS_VERTEX_COLLAPSOR_H_