// Copyright (c) 2007  INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v6.0.1/Spatial_sorting/include/CGAL/Hilbert_sort_median_3.h $
// $Id: include/CGAL/Hilbert_sort_median_3.h 50cfbde3b84 $
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Christophe Delage

#ifndef CGAL_HILBERT_SORT_MEDIAN_3_H
#define CGAL_HILBERT_SORT_MEDIAN_3_H

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

#ifdef CGAL_LINKED_WITH_TBB
#include <tbb/parallel_invoke.h>
#endif

namespace CGAL {

namespace internal {
template <class K, int x, bool up> struct Hilbert_cmp_3;

template <class K, int x>
struct Hilbert_cmp_3<K,x,true>
  : public CGAL::cpp98::binary_function<typename K::Point_3, typename K::Point_3, bool>
{
  typedef typename K::Point_3 Point;
  K k;
  Hilbert_cmp_3 (const K &_k) : k(_k) {}
  bool operator() (const Point &p, const Point &q) const
  {
    return Hilbert_cmp_3<K,x,false> (k) (q, p);
  }
};

template <class K>
struct Hilbert_cmp_3<K,0,false>
  : public CGAL::cpp98::binary_function<typename K::Point_3, typename K::Point_3, bool>
{
  typedef typename K::Point_3 Point;
  K k;
  Hilbert_cmp_3 (const K &_k) : k(_k) {}
  bool operator() (const Point &p, const Point &q) const
  {
    return k.less_x_3_object() (p, q);
  }
};

template <class K>
struct Hilbert_cmp_3<K,1,false>
  : public CGAL::cpp98::binary_function<typename K::Point_3, typename K::Point_3, bool>
{
  typedef typename K::Point_3 Point;
  K k;
  Hilbert_cmp_3 (const K &_k) : k(_k) {}
  bool operator() (const Point &p, const Point &q) const
  {
    return k.less_y_3_object() (p, q);
  }
};

template <class K>
struct Hilbert_cmp_3<K,2,false>
  : public CGAL::cpp98::binary_function<typename K::Point_3, typename K::Point_3, bool>
{
  typedef typename K::Point_3 Point;
  K k;
  Hilbert_cmp_3 (const K &_k) : k(_k) {}
  bool operator() (const Point &p, const Point &q) const
  {
    return k.less_z_3_object() (p, q);
  }
};

} // namespace internal

#ifdef __clang__
#define CGAL_VISIBILITY_MACRO __attribute__ ((visibility ("hidden")))
#else
#define CGAL_VISIBILITY_MACRO
#endif

template <class K, class ConcurrencyTag>
class CGAL_VISIBILITY_MACRO Hilbert_sort_median_3
{
public:
  typedef Hilbert_sort_median_3<K, ConcurrencyTag> Self;
  typedef K Kernel;
  typedef typename Kernel::Point_3 Point;

private:
  Kernel _k;
  std::ptrdiff_t _limit;

  template <int x, bool up>
  struct Cmp
    : public internal::Hilbert_cmp_3<Kernel,x,up>
  {
    Cmp (const Kernel &k) : internal::Hilbert_cmp_3<Kernel,x,up> (k) {}
  };

public:
  Hilbert_sort_median_3 (const Kernel &k, std::ptrdiff_t limit = 1)
    : _k(k), _limit (limit)
  {}

  template <int x, bool upx, bool upy, bool upz, class RandomAccessIterator>
  void recursive_sort (RandomAccessIterator begin, RandomAccessIterator end) const
  {
    const int y = (x + 1) % 3, z = (x + 2) % 3;
    if (end - begin <= _limit) return;

    RandomAccessIterator m0 = begin, m8 = end;

    RandomAccessIterator m4 = internal::hilbert_split (m0, m8, Cmp< x,  upx> (_k));
    RandomAccessIterator m2 = internal::hilbert_split (m0, m4, Cmp< y,  upy> (_k));
    RandomAccessIterator m1 = internal::hilbert_split (m0, m2, Cmp< z,  upz> (_k));
    RandomAccessIterator m3 = internal::hilbert_split (m2, m4, Cmp< z, !upz> (_k));
    RandomAccessIterator m6 = internal::hilbert_split (m4, m8, Cmp< y, !upy> (_k));
    RandomAccessIterator m5 = internal::hilbert_split (m4, m6, Cmp< z,  upz> (_k));
    RandomAccessIterator m7 = internal::hilbert_split (m6, m8, Cmp< z, !upz> (_k));

    recursive_sort<z, upz, upx, upy> (m0, m1);
    recursive_sort<y, upy, upz, upx> (m1, m2);
    recursive_sort<y, upy, upz, upx> (m2, m3);
    recursive_sort<x, upx,!upy,!upz> (m3, m4);
    recursive_sort<x, upx,!upy,!upz> (m4, m5);
    recursive_sort<y,!upy, upz,!upx> (m5, m6);
    recursive_sort<y,!upy, upz,!upx> (m6, m7);
    recursive_sort<z,!upz,!upx, upy> (m7, m8);
  }

  template <int x, bool upx, bool upy, bool upz, class RandomAccessIterator>
  struct Recursive_sort
  {
    const Self& hs;
    RandomAccessIterator begin,end;

    Recursive_sort(const Self& hs, RandomAccessIterator begin, RandomAccessIterator end)
      : hs(hs), begin(begin), end(end)
    {}

    void operator()() const
    {
      hs.recursive_sort<x,upx,upy,upz>(begin,end);
    }
  };

  template <class RandomAccessIterator, class Comp>
  struct Hilbert_split
  {
    RandomAccessIterator& res;
    RandomAccessIterator begin, end;
    const Comp& comp;

    Hilbert_split(RandomAccessIterator& res,
                  RandomAccessIterator begin, RandomAccessIterator end,
                  const Comp& comp)
      : res(res), begin(begin), end(end), comp(comp)
    {}

    void operator()() const
    {
      res = internal::hilbert_split(begin, end, comp);
    }
  };

  template <int x, bool upx, bool upy, bool upz, class RandomAccessIterator>
  void sort (RandomAccessIterator begin, RandomAccessIterator end, Parallel_tag) const
  {
#ifndef CGAL_LINKED_WITH_TBB
    CGAL_USE(begin);
    CGAL_USE(end);
    static_assert (!std::is_convertible<ConcurrencyTag, Parallel_tag>::value,
                   "Parallel_tag is enabled but TBB is unavailable.");
#else
    const int y = (x + 1) % 3, z = (x + 2) % 3;
    if ((end - begin) <= _limit) return;

    RandomAccessIterator m0 = begin, m8 = end;
    if((end - begin) > 2048){ // 2^11, empirically a good cutoff
      RandomAccessIterator m1, m2, m3, m4, m5, m6, m7;
      m4 = internal::hilbert_split(m0, m8, Cmp<x, upx>(_k));

      tbb::parallel_invoke(Hilbert_split<RandomAccessIterator,Cmp<y,  upy> >(m2, m0, m4, Cmp<y,  upy>(_k)),
                           Hilbert_split<RandomAccessIterator,Cmp<y, !upy> >(m6, m4, m8, Cmp<y, !upy>(_k)));

      tbb::parallel_invoke(Hilbert_split<RandomAccessIterator,Cmp<z,  upz> >(m1, m0, m2, Cmp<z,  upz>(_k)),
                           Hilbert_split<RandomAccessIterator,Cmp<z, !upz> >(m3, m2, m4, Cmp<z, !upz>(_k)),
                           Hilbert_split<RandomAccessIterator,Cmp<z,  upz> >(m5, m4, m6, Cmp<z,  upz>(_k)),
                           Hilbert_split<RandomAccessIterator,Cmp<z, !upz> >(m7, m6, m8, Cmp<z, !upz>(_k)));

      tbb::parallel_invoke(Recursive_sort<z,  upz,  upx,  upy, RandomAccessIterator>(*this, m0, m1),
                           Recursive_sort<y,  upy,  upz,  upx, RandomAccessIterator>(*this, m1, m2),
                           Recursive_sort<y,  upy,  upz,  upx, RandomAccessIterator>(*this, m2, m3),
                           Recursive_sort<x,  upx, !upy, !upz, RandomAccessIterator>(*this, m3, m4),
                           Recursive_sort<x,  upx, !upy, !upz, RandomAccessIterator>(*this, m4, m5),
                           Recursive_sort<y, !upy,  upz, !upx, RandomAccessIterator>(*this, m5, m6),
                           Recursive_sort<y, !upy,  upz, !upx, RandomAccessIterator>(*this, m6, m7),
                           Recursive_sort<z, !upz, !upx,  upy, RandomAccessIterator>(*this, m7, m8));
    } else {
      recursive_sort<0, false, false, false>(begin, end);
    }
#endif
  }

  template <int x, bool upx, bool upy, bool upz, class RandomAccessIterator>
  void sort (RandomAccessIterator begin, RandomAccessIterator end, Sequential_tag) const
  {
    recursive_sort<0, false, false, false>(begin, end);
  }

  template <class RandomAccessIterator>
  void operator() (RandomAccessIterator begin, RandomAccessIterator end) const
  {
    sort <0, false, false, false> (begin, end, ConcurrencyTag());
  }
};

} // namespace CGAL

#endif//CGAL_HILBERT_SORT_MEDIAN_3_H

