// Copyright (c) 1999
// Max-Planck-Institute Saarbruecken (Germany). All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1.2/Point_set_2/include/CGAL/nearest_neighbor_delaunay_2.h $
// $Id: include/CGAL/nearest_neighbor_delaunay_2.h 37e2b278910 $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Matthias Baesken

#ifndef CGAL_NEAREST_NEIGHBOR_DELAUNAY_2_H
#define CGAL_NEAREST_NEIGHBOR_DELAUNAY_2_H

#include <CGAL/license/Point_set_2.h>


#include <CGAL/basic.h>
#include <CGAL/Unique_hash_map.h>
#include <CGAL/Delaunay_triangulation_2.h>
#include <CGAL/compare_vertices.h>
#include <list>
#include <queue>
#include <map>
#include <stack>
#include <cmath>

namespace CGAL {



template<class Dt>
typename Dt::Vertex_handle  nearest_neighbor(const Dt& delau, typename Dt::Vertex_handle v)
{
  typedef typename Dt::Geom_traits                    Gt;
  typedef typename Dt::Point                          Point;
  typedef typename Dt::Vertex_circulator              Vertex_circulator;
  typedef typename Dt::Vertex_handle                  Vertex_handle;
  typedef typename Gt::Compare_distance_2             Compare_dist_2;

  if (delau.number_of_vertices() <= 1) return nullptr;
  Point p = v->point();

  Vertex_circulator vc = delau.incident_vertices(v);
  Vertex_circulator start =vc;

  Vertex_handle min_v = vc;
  if (delau.is_infinite(min_v)){
     vc++;
     min_v = vc;
  }

  Vertex_handle act;

  // go through the vertices ...
  do {
       act = vc;

       if (! delau.is_infinite(act)) {
        if ( Compare_dist_2()(p,act->point(), min_v->point()) == SMALLER ) min_v = act;
       }

       vc++;
  } while (vc != start);

  return min_v;
}


template<class Dt>
typename Dt::Vertex_handle lookup(const Dt& delau, const typename Dt::Point& p)
{
 typedef typename Dt::Face                      Face;
 typedef typename Dt::Locate_type               Locate_type;
 typedef typename Dt::Face_handle               Face_handle;

 if (delau.number_of_vertices() == 0) return nullptr;

 // locate ...
 Locate_type lt;
 int li;
 Face_handle fh = delau.locate(p,lt,li);

 if (lt == Dt::VERTEX){
      Face f = *fh;
      return f.vertex(li);
 }
 else return nullptr;
}


template<class Dt, class OutputIterator>
OutputIterator   nearest_neighbors(Dt& delau, const typename Dt::Point& p, std::size_t k, OutputIterator res)
{
  typedef typename Dt::size_type                      size_type;
  typedef typename Dt::Vertex_handle                  Vertex_handle;
  typedef typename Dt::Vertex_iterator                Vertex_iterator;

   size_type n = delau.number_of_vertices();

   if ( k <= 0 ) return res;
   if ( n <= k ) { // return all finite vertices ...

     Vertex_iterator vit = delau.finite_vertices_begin();
     for (; vit != delau.finite_vertices_end(); vit++) { *res= vit; res++; }

     return res;
   }

   // insert p, if necessary

   Vertex_handle vh = lookup(delau,p);
   bool old_node = true;

   // we have to add a new vertex ...
   if (vh == nullptr){
      vh = delau.insert(p);
      old_node = false;
      k++;
   }

   std::list<Vertex_handle> res_list;
   nearest_neighbors_list(delau, vh, k, res_list);

   if ( !old_node )
   {
     res_list.pop_front();
     delau.remove(vh);
   }

   typename std::list<Vertex_handle>::iterator it = res_list.begin();

   for (; it != res_list.end(); it++) { *res= *it; res++; }
   return res;
}



template<class Dt, class OutputIterator>
OutputIterator  nearest_neighbors(const Dt& delau, typename Dt::Vertex_handle v, std::size_t k, OutputIterator res)
{
  typedef typename Dt::size_type                      size_type;
  typedef typename Dt::Vertex_handle                  Vertex_handle;
  typedef typename Dt::Vertex_iterator                Vertex_iterator;

   size_type n = delau.number_of_vertices();

   if ( k <= 0 ) return res;
   if ( n <= k ) { // return all (finite) vertices ...

     Vertex_iterator vit = delau.finite_vertices_begin();
     for (; vit != delau.finite_vertices_end(); vit++) { *res= vit; res++; }

     return res;
   }

   std::list<Vertex_handle> res_list;
   nearest_neighbors_list(delau, v, k, res_list);

   typename std::list<Vertex_handle>::iterator it = res_list.begin();

   for (; it != res_list.end(); it++) { *res= *it; res++; }

   return res;
}


template<class Dt, class OutputIterator>
OutputIterator get_vertices(const Dt& delau, OutputIterator res)
{
  typedef typename Dt::Vertex_iterator                Vertex_iterator;

  Vertex_iterator vit = delau.finite_vertices_begin();
  for (; vit != delau.finite_vertices_end(); vit++) { *res= vit; res++; }
  return res;
}


// second template argument for VC ...

template<class Dt, class T2>
void nearest_neighbors_list(const Dt& delau, typename Dt::Vertex_handle v, std::size_t k, std::list<T2>& res)
{
  typedef typename Dt::Geom_traits                    Gt;
  typedef typename Dt::size_type                      size_type;
  typedef typename Dt::Vertex_handle                  Vertex_handle;
  typedef typename Dt::Vertex_circulator              Vertex_circulator;
  typedef typename Dt::Point                          Point;
  typedef typename Gt::FT                             Numb_type;  // field number type ...
  typedef typename Gt::Compute_squared_distance_2     Compute_squared_distance_2;
  typedef Unique_hash_map<Vertex_handle, Numb_type>         MAP_TYPE;

  size_type n = delau.number_of_vertices();

  if ( k <= 0 ) return;
  if ( n <= k ) {
      get_vertices(delau, std::back_inserter(res));
      return;
  }

  Point p = v->point();

  Unique_hash_map<Vertex_handle, int>  mark;
  int cur_mark = 1;

  MAP_TYPE  priority_number; // here we save the priorities ...

  internal::compare_vertices<Vertex_handle,Numb_type,MAP_TYPE> comp(& priority_number);      // comparison object ...
  std::priority_queue<Vertex_handle, std::vector<Vertex_handle>, internal::compare_vertices<Vertex_handle,Numb_type,MAP_TYPE> > PQ(comp);

  priority_number[v] = 0;
  PQ.push(v);

  // mark vertex v
  mark[v] = cur_mark;

  while ( k > 0 )
  {
    // find minimum from PQ ...
    Vertex_handle w = PQ.top();
    PQ.pop();

    res.push_back(w);
    k--;

    // get the incident vertices of w ...
    Vertex_circulator vc = delau.incident_vertices(w);
    Vertex_circulator start =vc;
    Vertex_handle act;

    do {
         act = vc;

         // test, if act is marked ...
         bool is_marked = mark.is_defined(act);

         if ( (! is_marked) && (! delau.is_infinite(act)) )
         {
             priority_number[act] = Compute_squared_distance_2()(p,act->point());
             PQ.push(act);
             mark[act] = cur_mark;
         }

         vc++;
       } while (vc != start);

   }
}


} //namespace CGAL

#endif
