#include <CGAL/Simple_cartesian.h>
#include <CGAL/Surface_mesh.h>
#include <CGAL/Mean_curvature_flow_skeletonization.h>

#include <fstream>

typedef CGAL::Simple_cartesian<double>                        Kernel;
typedef Kernel::Point_3                                       Point;
typedef CGAL::Surface_mesh<Point>                             Triangle_mesh;

typedef boost::graph_traits<Triangle_mesh>::vertex_descriptor vertex_descriptor;

typedef CGAL::Mean_curvature_flow_skeletonization<Triangle_mesh> Skeletonization;
typedef Skeletonization::Skeleton                             Skeleton;

typedef Skeleton::vertex_descriptor                           Skeleton_vertex;
typedef Skeleton::edge_descriptor                             Skeleton_edge;

int main(int argc, char* argv[])
{
  std::ifstream input((argc>1)?argv[1]:CGAL::data_file_path("meshes/elephant.off"));
  Triangle_mesh tmesh;
  input >> tmesh;
  if (!CGAL::is_triangle_mesh(tmesh))
  {
    std::cout << "Input geometry is not triangulated." << std::endl;
    return EXIT_FAILURE;
  }

  Skeleton skeleton;
  Skeletonization mcs(tmesh);

  // 1. Contract the mesh by mean curvature flow.
  mcs.contract_geometry();

  // 2. Collapse short edges and split bad triangles.
  mcs.collapse_edges();
  mcs.split_faces();

  // 3. Fix degenerate vertices.
  mcs.detect_degeneracies();

  // Perform the above three steps in one iteration.
  mcs.contract();

  // Iteratively apply step 1 to 3 until convergence.
  mcs.contract_until_convergence();

  // Convert the contracted mesh into a curve skeleton and
  // get the correspondent surface points
  mcs.convert_to_skeleton(skeleton);

  std::cout << "Number of vertices of the skeleton: " << boost::num_vertices(skeleton) << "\n";
  std::cout << "Number of edges of the skeleton: " << boost::num_edges(skeleton) << "\n";

  // Output all the edges of the skeleton.
  std::ofstream output("skel-sm.polylines.txt");
  for(Skeleton_edge e : CGAL::make_range(edges(skeleton)))
  {
    const Point& s = skeleton[source(e, skeleton)].point;
    const Point& t = skeleton[target(e, skeleton)].point;
    output << "2 "<< s << " " << t << "\n";
  }
  output.close();

  // Output skeleton points and the corresponding surface points
  output.open("correspondence-sm.polylines.txt");
  for(Skeleton_vertex v : CGAL::make_range(vertices(skeleton)))
    for(vertex_descriptor vd : skeleton[v].vertices)
      output << "2 " << skeleton[v].point << "  " << get(CGAL::vertex_point, tmesh, vd)  << "\n";

  return EXIT_SUCCESS;
}
