// Copyright (c) 2007-09  INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v5.1/Point_set_processing_3/include/CGAL/grid_simplify_point_set.h $
// $Id: grid_simplify_point_set.h c253679 2020-04-18T16:27:58+02:00 Sébastien Loriot
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s) : Nader Salman and Laurent Saboret

#ifndef CGAL_GRID_SIMPLIFY_POINT_SET_H
#define CGAL_GRID_SIMPLIFY_POINT_SET_H

#include <CGAL/license/Point_set_processing_3.h>

#include <CGAL/disable_warnings.h>

#include <CGAL/property_map.h>
#include <CGAL/Kernel_traits.h>
#include <CGAL/point_set_processing_assertions.h>
#include <CGAL/Iterator_range.h>
#include <functional>
#include <boost/functional/hash.hpp>

#include <CGAL/boost/graph/Named_function_parameters.h>
#include <CGAL/boost/graph/named_params_helper.h>

#include <iterator>
#include <deque>
#include <algorithm>
#include <cmath>
#include <unordered_set>

namespace CGAL {


// ----------------------------------------------------------------------------
// Private section
// ----------------------------------------------------------------------------
/// \cond SKIP_IN_MANUAL

namespace internal {


// Round number to multiples of epsilon
inline double round_epsilon(double value, double epsilon)
{
  return std::floor(value / epsilon);
}

/// Utility class for grid_simplify_point_set(): Hash_epsilon_points_3
/// defines a 3D point hash / 2 points are equal iff they belong to
/// the same cell of a grid of cell size = epsilon.
template <class Point_3, class PointMap>
struct Hash_epsilon_points_3
{
private:

    double m_epsilon;
    PointMap point_map;
    typedef typename boost::property_traits<PointMap>::value_type Point;
public:

    Hash_epsilon_points_3 (double epsilon, PointMap p_map)
        : m_epsilon (epsilon), point_map(p_map)
    {
        CGAL_point_set_processing_precondition(epsilon > 0);
    }

  std::size_t operator() (const Point_3& a) const
  {
    const Point& pa = get(point_map,a);
    std::size_t result = boost::hash_value(round_epsilon(pa.x(), m_epsilon));
    boost::hash_combine(result, boost::hash_value(round_epsilon(pa.y(), m_epsilon)));
    boost::hash_combine(result, boost::hash_value(round_epsilon(pa.z(), m_epsilon)));
    return result;
  }

};

/// Utility class for grid_simplify_point_set(): Hash_epsilon_points_3
/// defines a 3D point equality / 2 points are equal iff they belong
/// to the same cell of a grid of cell size = epsilon.
template <class Point_3, class PointMap>
struct Equal_epsilon_points_3
{
private:

    const double m_epsilon;
    PointMap point_map;
    typedef typename boost::property_traits<PointMap>::value_type Point;
public:

    Equal_epsilon_points_3 (const double& epsilon, PointMap p_map)
        : m_epsilon (epsilon), point_map(p_map)
    {
        CGAL_point_set_processing_precondition(epsilon > 0);
    }

    bool operator() (const Point_3& a, const Point_3& b) const
    {
      const Point& pa = get(point_map,a);
      const Point& pb = get(point_map,b);

      double ra = round_epsilon(pa.x(), m_epsilon);
      double rb = round_epsilon(pb.x(), m_epsilon);
      if (ra != rb)
        return false;
      ra = round_epsilon(pa.y(), m_epsilon);
      rb = round_epsilon(pb.y(), m_epsilon);
      if (ra != rb)
        return false;
      ra = round_epsilon(pa.z(), m_epsilon);
      rb = round_epsilon(pb.z(), m_epsilon);
      return ra == rb;
    }
};


} /* namespace internal */


/// Utility class for grid_simplify_point_set():
/// 3D points set which allows at most 1 point per cell
/// of a grid of cell size = epsilon.
///
/// Warning:
/// This class is a container sorted wrt points position
/// => you should not modify directly the order or the position of points.

template <class Point_3, class PointMap>
class Epsilon_point_set_3
  : public std::unordered_set<Point_3,
                                internal::Hash_epsilon_points_3<Point_3, PointMap>,
                                internal::Equal_epsilon_points_3<Point_3, PointMap> >
{
private:

    // superclass
    typedef std::unordered_set<Point_3,
                                internal::Hash_epsilon_points_3<Point_3, PointMap>,
                                internal::Equal_epsilon_points_3<Point_3, PointMap> > Base;

public:

    Epsilon_point_set_3 (double epsilon, PointMap point_map)
        : Base(10, internal::Hash_epsilon_points_3<Point_3, PointMap>(epsilon, point_map),
               internal::Equal_epsilon_points_3<Point_3, PointMap>(epsilon, point_map))
    {
        CGAL_point_set_processing_precondition(epsilon > 0);
    }

    // default copy constructor, operator =() and destructor are fine.
};

/// \endcond

// ----------------------------------------------------------------------------
// Public section
// ----------------------------------------------------------------------------

/**
   \ingroup PkgPointSetProcessing3Algorithms
   Merges points which belong to the same cell of a grid of cell size = `epsilon`.

   This method modifies the order of input points so as to pack all remaining points first,
   and returns an iterator over the first point to remove (see erase-remove idiom).
   For this reason it should not be called on sorted containers.

   \pre `epsilon > 0`

   \tparam PointRange is a model of `Range`. The value type of
   its iterator is the key type of the named parameter `point_map`.

   \param points input point range.
   \param epsilon tolerance value when merging 3D points.
   \param np an optional sequence of \ref bgl_namedparameters "Named Parameters" among the ones listed below

   \cgalNamedParamsBegin
     \cgalParamNBegin{point_map}
       \cgalParamDescription{a property map associating points to the elements of the point set `points`}
       \cgalParamType{a model of `ReadWritePropertyMap` whose key type is the value type
                      of the iterator of `PointRange` and whose value type is `geom_traits::Point_3`}
       \cgalParamDefault{`CGAL::Identity_property_map<geom_traits::Point_3>`}
     \cgalParamNEnd

     \cgalParamNBegin{callback}
       \cgalParamDescription{a mechanism to get feedback on the advancement of the algorithm
                             while it's running and to interrupt it if needed}
       \cgalParamType{an instance of `std::function<bool(double)>`.}
       \cgalParamDefault{unused}
       \cgalParamExtra{It is called regularly when the
                       algorithm is running: the current advancement (between 0. and
                       1.) is passed as parameter. If it returns `true`, then the
                       algorithm continues its execution normally; if it returns
                       `false`, the algorithm is stopped and simplification stops with no guarantee on the output. }
       \cgalParamExtra{The callback will be copied and therefore needs to be lightweight.}
     \cgalParamNEnd

     \cgalParamNBegin{geom_traits}
       \cgalParamDescription{an instance of a geometric traits class}
       \cgalParamType{a model of `Kernel`}
       \cgalParamDefault{a \cgal Kernel deduced from the point type, using `CGAL::Kernel_traits`}
     \cgalParamNEnd
   \cgalNamedParamsEnd

   \return iterator over the first point to remove.
*/
template <typename PointRange, typename NamedParameters>
typename PointRange::iterator
grid_simplify_point_set(
  PointRange& points,
  double epsilon,
  const NamedParameters& np)
{
  using parameters::choose_parameter;
  using parameters::get_parameter;

  typedef typename CGAL::GetPointMap<PointRange, NamedParameters>::const_type PointMap;
  PointMap point_map = choose_parameter<PointMap>(get_parameter(np, internal_np::point_map));
  const std::function<bool(double)>& callback = choose_parameter(get_parameter(np, internal_np::callback),
                                                                 std::function<bool(double)>());

  // actual type of input points
  typedef typename std::iterator_traits<typename PointRange::iterator>::value_type Enriched_point;

  CGAL_point_set_processing_precondition(epsilon > 0);

  // Merges points which belong to the same cell of a grid of cell size = epsilon.
  // points_to_keep[] will contain 1 point per cell; the others will be in points_to_remove[].
  Epsilon_point_set_3<Enriched_point, PointMap> points_to_keep(epsilon, point_map);
  std::deque<Enriched_point> points_to_remove;
  std::size_t nb = 0, nb_points = points.size();
  for (typename PointRange::iterator it = points.begin(); it != points.end(); it++, ++ nb)
  {
    std::pair<typename Epsilon_point_set_3<Enriched_point, PointMap>::iterator,bool> result;
    result = points_to_keep.insert(*it);
    if (!result.second) // if not inserted
      points_to_remove.push_back(*it);
    if (callback && !callback ((nb+1) / double(nb_points)))
      break;
  }

  // Replaces `[first, beyond)` range by the content of points_to_keep, then points_to_remove.
  typename PointRange::iterator first_point_to_remove =
    std::copy(points_to_keep.begin(), points_to_keep.end(), points.begin());
    std::copy(points_to_remove.begin(), points_to_remove.end(), first_point_to_remove);

  return first_point_to_remove;
}

/// \cond SKIP_IN_MANUAL
// variant with default NP
template <typename PointRange>
typename PointRange::iterator
grid_simplify_point_set(PointRange& points, double epsilon)
{
  return grid_simplify_point_set
    (points, epsilon, CGAL::Point_set_processing_3::parameters::all_default(points));
}
/// \endcond


} //namespace CGAL

#include <CGAL/enable_warnings.h>

#endif // CGAL_GRID_SIMPLIFY_POINT_SET_H