// Copyright (c) 2011  INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v5.6.1/Spatial_sorting/include/CGAL/Hilbert_sort_median_d.h $
// $Id: Hilbert_sort_median_d.h f60dfa8 2022-04-04T10:00:16+02:00 Sébastien Loriot
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     :  Olivier Devillers

#ifndef CGAL_HILBERT_SORT_MEDIAN_d_H
#define CGAL_HILBERT_SORT_MEDIAN_d_H

#include <CGAL/config.h>
#include <functional>
#include <cstddef>
#include <iterator>
#include <vector>
#include <CGAL/Hilbert_sort_base.h>

namespace CGAL {

namespace internal {

template <class K>
struct Hilbert_cmp_d
    : public CGAL::cpp98::binary_function<typename K::Point_d,
    typename K::Point_d, bool>
{
  typedef typename K::Point_d Point;
  K k;
  int axe;
  bool orient;
  Hilbert_cmp_d (int a, bool o, const K &_k) : k(_k), axe(a),  orient(o) {}

  bool operator() (const Point &p, const Point &q) const
  {
    return (orient  ? (k.less_coordinate_d_object() (q,p,axe) )
                    : (k.less_coordinate_d_object() (p,q,axe) ));
  }
};

} // namespace internal

template <class K>
class Hilbert_sort_median_d
{
public:
  typedef K Kernel;
  typedef typename Kernel::Point_d Point;
  typedef std::vector< bool > Starting_position;

private:
  Kernel _k;
  std::ptrdiff_t _limit;
  mutable int _dimension;
  mutable int two_to_dim;

  struct Cmp
    : public internal::Hilbert_cmp_d<Kernel>
  {
    Cmp (int a, bool dir, const Kernel &k) : internal::Hilbert_cmp_d<Kernel> (a,dir,k) {}
  };

public:
  Hilbert_sort_median_d(const Kernel &k, std::ptrdiff_t limit = 1)
    : _k(k), _limit (limit)
  {}

  template <class RandomAccessIterator>
  void sort (RandomAccessIterator begin, RandomAccessIterator end,
             Starting_position start, int direction) const
  {
    if (end - begin <= _limit)
      return;

    int nb_directions = _dimension;
    int nb_splits     = two_to_dim;

    if ( (end-begin) < (two_to_dim/2) ) { // not many points
      nb_splits = 1;
      nb_directions = 0;
      while ( (end-begin) > nb_splits) {
        ++nb_directions;
        nb_splits *= 2;        // compute 2^nb_directions
      }
    }

    std::vector<RandomAccessIterator> places(nb_splits +1);
    std::vector<int>                  dir   (nb_splits +1);
    places[0]=begin;
    places[nb_splits]=end;

    int last_dir = (direction + nb_directions) % _dimension;
    int current_dir = direction;
    int current_level_step =nb_splits;
    do{
      int half_step = current_level_step/2;
      int left=0;
      int middle = half_step;
      int right=current_level_step;
      bool orient = start[current_dir];
      do{
        dir[middle]    = current_dir;
        places[middle] = internal::hilbert_split
                         (places[left], places[right], Cmp (current_dir,orient,_k));
        left =right;
        right+=current_level_step;
        middle+=current_level_step;
        orient = ! orient;
      }while( left< nb_splits);
      current_level_step = half_step;
      current_dir = (current_dir +1) % _dimension;
    }while (current_dir != last_dir);

    if ( end-begin < two_to_dim) return; // fewer than 2^dim points

    /////////////start recursive calls
    last_dir = (direction + _dimension -1) % _dimension;
    // first step is special
    sort( places[0], places[1], start, last_dir);

    for(int i=1; i<two_to_dim-1; i +=2){
      sort( places[i  ], places[i+1], start, dir[i+1]);
      sort( places[i+1], places[i+2], start, dir[i+1]);
      start[dir[i+1]] = !  start[dir[i+1]];
      start[last_dir] = !  start[last_dir];
    }

    //last step is special
    sort( places[two_to_dim-1], places[two_to_dim], start, last_dir);
  }

  template <class RandomAccessIterator>
  void operator() (RandomAccessIterator begin, RandomAccessIterator end) const
  {
    _dimension = _k.point_dimension_d_object()(*begin);
    two_to_dim = 1;
    Starting_position start(_dimension);

    typename std::iterator_traits<RandomAccessIterator>::difference_type N=end-begin;
    N*=2;
    for (int i=0; i<_dimension; ++i)
      start[i]=false; // we start below in all coordinates

    for (int i=0; i<_dimension; ++i) {
      two_to_dim *= 2;        // compute 2^_dimension
      N/=2;
      if (N==0)
        break;  // not many points, this number of dimension is enough
    }

    // we start with  direction 0;
    sort (begin, end, start, 0);
  }
};

} // namespace CGAL

#endif//CGAL_HILBERT_SORT_MEDIAN_d_H

