// Copyright (c) 2002,2011,2014 Utrecht University (The Netherlands), Max-Planck-Institute Saarbruecken (Germany).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
//
// $URL: https://github.com/CGAL/cgal/blob/v6.1.1/Spatial_searching/include/CGAL/Kd_tree.h $
// $Id: include/CGAL/Kd_tree.h 08b27d3db14 $
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Hans Tangelder (<hanst@cs.uu.nl>),
//               : Waqar Khan <wkhan@mpi-inf.mpg.de>,
//                 Clement Jamin (clement.jamin.pro@gmail.com)

#ifndef CGAL_KD_TREE_H
#define CGAL_KD_TREE_H

#include <CGAL/license/Spatial_searching.h>

#include <CGAL/disable_warnings.h>

#include <CGAL/basic.h>
#include <CGAL/assertions.h>
#include <vector>
#include <string>
#include <unordered_map>
#include <ostream>

#include <CGAL/algorithm.h>
#include <CGAL/Kd_tree_node.h>
#include <CGAL/Splitters.h>
#include <CGAL/Spatial_searching/internal/Get_dimension_tag.h>

#include <boost/container/deque.hpp>
#include <optional>

#ifdef CGAL_HAS_THREADS
#include <CGAL/mutex.h>
#endif

/*
  For building the KD Tree in parallel, TBB is needed. If TBB is
  linked, the internal structures `deque` will be replaced by
  `tbb::concurrent_vector`, even if the KD Tree is built in sequential
  mode (this is to avoid changing the type of the KD Tree when
  changing the concurrency mode of `build()`).

  Experimentally, using the `tbb::concurrent_vector` in sequential
  mode does not trigger any loss of performance, so from a user's
  point of view, it should be transparent.

  However, in case one wants to compile the KD Tree *without using TBB
  structure even though CGAL is linked with TBB*, the macro
  `CGAL_DISABLE_TBB_STRUCTURE_IN_KD_TREE` can be defined. In that
  case, even if TBB is linked, the standard `deque` will be used
  internally. Note that of course, in that case, parallel build will
  be disabled.
 */
#if defined(CGAL_LINKED_WITH_TBB) && !defined(CGAL_DISABLE_TBB_STRUCTURE_IN_KD_TREE)
#  include <tbb/parallel_invoke.h>
#  include <tbb/concurrent_vector.h>
#  define CGAL_TBB_STRUCTURE_IN_KD_TREE
#endif

namespace CGAL {

//template <class SearchTraits, class Splitter_=Median_of_rectangle<SearchTraits>, class UseExtendedNode = Tag_true >
template <
  class SearchTraits,
  class Splitter_=Sliding_midpoint<SearchTraits>,
  class UseExtendedNode = Tag_true,
  class EnablePointsCache = Tag_false>
class Kd_tree {

public:
  typedef SearchTraits Traits;
  typedef Splitter_ Splitter;
  typedef typename SearchTraits::Point_d Point_d;
  typedef typename Splitter::Container Point_container;

  typedef typename SearchTraits::FT FT;
  typedef Kd_tree_node<SearchTraits, Splitter, UseExtendedNode, EnablePointsCache> Node;
  typedef Kd_tree_leaf_node<SearchTraits, Splitter, UseExtendedNode, EnablePointsCache> Leaf_node;
  typedef Kd_tree_internal_node<SearchTraits, Splitter, UseExtendedNode, EnablePointsCache> Internal_node;
  typedef Kd_tree<SearchTraits, Splitter, UseExtendedNode, EnablePointsCache> Tree;
  typedef Kd_tree<SearchTraits, Splitter, UseExtendedNode, EnablePointsCache> Self;

  typedef Node* Node_handle;
  typedef const Node* Node_const_handle;
  typedef Leaf_node* Leaf_node_handle;
  typedef const Leaf_node* Leaf_node_const_handle;
  typedef Internal_node* Internal_node_handle;
  typedef const Internal_node* Internal_node_const_handle;
  typedef typename std::vector<const Point_d*>::const_iterator Point_d_iterator;
  typedef typename std::vector<const Point_d*>::const_iterator Point_d_const_iterator;
  typedef typename Splitter::Separator Separator;
  typedef typename std::vector<Point_d>::const_iterator iterator;
  typedef typename std::vector<Point_d>::const_iterator const_iterator;

  typedef typename std::vector<Point_d>::size_type size_type;

  typedef typename internal::Get_dimension_tag<SearchTraits>::Dimension D;

  typedef EnablePointsCache Enable_points_cache;

private:

  SearchTraits traits_;
  Splitter split;

#if defined(CGAL_TBB_STRUCTURE_IN_KD_TREE)
  tbb::concurrent_vector<Internal_node> internal_nodes;
  tbb::concurrent_vector<Leaf_node> leaf_nodes;
#else
  boost::container::deque<Internal_node> internal_nodes;
  boost::container::deque<Leaf_node> leaf_nodes;
#endif

  Node_handle tree_root;

  Kd_tree_rectangle<FT,D>* bbox;
  std::vector<Point_d> pts;

  // Store a contiguous copy of the point coordinates
  // for faster queries (reduce the number of cache misses)
  std::vector<FT> points_cache;

  // Instead of storing the points in arrays in the Kd_tree_node
  // we put all the data in a vector in the Kd_tree.
  // and we only store an iterator range in the Kd_tree_node.
  //
  std::vector<const Point_d*> data;

  // Dimension of the points
  int dim_;

  #ifdef CGAL_HAS_THREADS
  mutable CGAL_MUTEX building_mutex;//mutex used to protect const calls inducing build()
  #endif
  bool built_;
  std::size_t removed_=0;

  // protected copy constructor
  Kd_tree(const Tree& tree)
    : traits_(tree.traits_),built_(tree.built_),dim_(-1)
  {};

  // Instead of the recursive construction of the tree in the class Kd_tree_node
  // we do this in the tree class. The advantage is that we then can optimize
  // the allocation of the nodes.

  // The leaf node
  Node_handle
  create_leaf_node(Point_container& c)
  {
    Leaf_node node(static_cast<unsigned int>(c.size()));
    std::ptrdiff_t tmp = c.begin() - data.begin();
    node.data = pts.begin() + tmp;

#ifdef CGAL_TBB_STRUCTURE_IN_KD_TREE
    return &*(leaf_nodes.push_back(node));
#else
    leaf_nodes.emplace_back (node);
    return &(leaf_nodes.back());
#endif
  }

  // The internal node
  Node_handle new_internal_node()
  {
#ifdef CGAL_TBB_STRUCTURE_IN_KD_TREE
    return &*(internal_nodes.push_back(Internal_node()));
#else
    internal_nodes.emplace_back ();
    return &(internal_nodes.back());
#endif
  }

  // TODO: Similar to the leaf_init function above, a part of the code should be
  //       moved to a the class Kd_tree_node.
  //       It is not proper yet, but the goal was to see if there is
  //       a potential performance gain through the Compact_container
  template <typename ConcurrencyTag>
  void
  create_internal_node(Node_handle n, Point_container& c, const ConcurrencyTag& tag)
  {
    Internal_node_handle nh = static_cast<Internal_node_handle>(n);
    CGAL_assertion (nh != nullptr);

    Separator sep;
    Point_container c_low(c.dimension(),traits_);
    split(sep, c, c_low);
    nh->set_separator(sep);

    handle_extended_node (nh, c, c_low, UseExtendedNode());

    if (try_parallel_internal_node_creation (nh, c, c_low, tag))
      return;

    if (c_low.size() > split.bucket_size() && !CGAL::is_zero(c_low.max_tight_spread()))
    {
      nh->lower_ch = new_internal_node();
      create_internal_node (nh->lower_ch, c_low, tag);
    }
    else
      nh->lower_ch = create_leaf_node(c_low);

    if (c.size() > split.bucket_size() && !CGAL::is_zero(c.max_tight_spread()))
    {
      nh->upper_ch = new_internal_node();
      create_internal_node (nh->upper_ch, c, tag);
    }
    else
      nh->upper_ch = create_leaf_node(c);
  }

  void handle_extended_node (Internal_node_handle nh, Point_container& c, Point_container& c_low, const Tag_true&)
  {
    int cd  = nh->cutting_dimension();
    if(!c_low.empty()){
      nh->lower_low_val = c_low.tight_bounding_box().min_coord(cd);
      nh->lower_high_val = c_low.tight_bounding_box().max_coord(cd);
    }
    else{
      nh->lower_low_val = nh->cutting_value();
      nh->lower_high_val = nh->cutting_value();
    }
    if(!c.empty()){
      nh->upper_low_val = c.tight_bounding_box().min_coord(cd);
      nh->upper_high_val = c.tight_bounding_box().max_coord(cd);
    }
    else{
      nh->upper_low_val = nh->cutting_value();
      nh->upper_high_val = nh->cutting_value();
    }

    CGAL_assertion(nh->cutting_value() >= nh->lower_low_val);
    CGAL_assertion(nh->cutting_value() <= nh->upper_high_val);
  }

  inline void handle_extended_node (Internal_node_handle, Point_container&, Point_container&, const Tag_false&) { }

  inline bool try_parallel_internal_node_creation (Internal_node_handle, Point_container&,
                                                   Point_container&, const Sequential_tag&)
  {
    return false;
  }

#ifdef CGAL_TBB_STRUCTURE_IN_KD_TREE

  inline bool try_parallel_internal_node_creation (Internal_node_handle nh, Point_container& c,
                                                   Point_container& c_low, const Parallel_tag& tag)
  {
    /*
      The two child branches are computed in parallel if and only if:

      * both branches lead to internal nodes (if at least one branch
        is a leaf, it's useless)

      * the current number of points is sufficiently high to be worth
        the cost of launching new threads. Experimentally, using 10
        times the bucket size as a limit gives the best timings.
    */
    if (c_low.size() > split.bucket_size() && c.size() > split.bucket_size()
        && (c_low.size() + c.size() > 10 * split.bucket_size()))
    {
      nh->lower_ch = new_internal_node();
      nh->upper_ch = new_internal_node();
      tbb::parallel_invoke (std::bind (&Self::create_internal_node<Parallel_tag>, this, nh->lower_ch, std::ref(c_low), std::cref(tag)),
                            std::bind (&Self::create_internal_node<Parallel_tag>, this, nh->upper_ch, std::ref(c), std::cref(tag)));
      return true;
    }

    return false;
  }

#endif

public:

  Kd_tree(Splitter s = Splitter(),const SearchTraits traits=SearchTraits())
    : traits_(traits),split(s), built_(false)
  {}

  template <class InputIterator>
  Kd_tree(InputIterator first, InputIterator beyond,
          Splitter s = Splitter(),const SearchTraits traits=SearchTraits())
    : traits_(traits), split(s), pts(first, beyond), built_(false)
  { }

  template <class PointRange>
  Kd_tree(const PointRange& points,
          Splitter s = Splitter(), const SearchTraits traits = SearchTraits())
    : traits_(traits),
      split(s),
      pts(std::begin(points), std::end(points)),
      built_(false)
  { }

  bool empty() const {
    return pts.empty();
  }

  void build()
  {
    build<Sequential_tag>();
  }

  /*
    Note about parallel `build()`. Several different strategies have
    been tried, among which:

    * keeping the `deque` and using mutex structures to secure the
      insertions in them
    * using free stand-alone pointers generated with `new` instead of
      pushing elements in a container
    * using a global `tbb::task_group` to handle the internal node
      computations
    * using one `tbb::task_group` per internal node to handle the
      internal node computations

    Experimentally, the options giving the best timings is the one
    kept, namely:

    * nodes are stored in `tbb::concurrent_vector` structures
    * the parallel computations are launched using
      `tbb::parallel_invoke`
  */
  template <typename ConcurrencyTag>
  void
  build()
  {
    // This function is not ready to be called when a tree already exists, one
    // must call invalidate_build() first.
    CGAL_assertion(!is_built());
    CGAL_assertion(!pts.empty());
    CGAL_assertion(removed_==0);
    const Point_d& p = *pts.begin();
    typename SearchTraits::Construct_cartesian_const_iterator_d ccci=traits_.construct_cartesian_const_iterator_d_object();
    dim_ = static_cast<int>(std::distance(ccci(p), ccci(p,0)));

    data.reserve(pts.size());
    for(std::size_t i = 0; i < pts.size(); i++){
      data.push_back(&pts[i]);
    }

#ifndef CGAL_TBB_STRUCTURE_IN_KD_TREE
    static_assert (!(std::is_convertible<ConcurrencyTag, Parallel_tag>::value),
                               "Parallel_tag is enabled but TBB is unavailable.");
#endif

    Point_container c(dim_, data.begin(), data.end(),traits_);
    bbox = new Kd_tree_rectangle<FT,D>(c.bounding_box());
    if (c.size() <= split.bucket_size() || CGAL::is_zero(c.max_tight_spread())){
      tree_root = create_leaf_node(c);
    }else {
       tree_root = new_internal_node();
       create_internal_node (tree_root, c, ConcurrencyTag());
    }

    //Reorder vector for spatial locality
    std::vector<Point_d> ptstmp;
    ptstmp.resize(pts.size());
    for (std::size_t i = 0; i < pts.size(); ++i)
      ptstmp[i] = *data[i];

    // Cache?
    if (Enable_points_cache::value)
    {
      typename SearchTraits::Construct_cartesian_const_iterator_d construct_it = traits_.construct_cartesian_const_iterator_d_object();
      points_cache.reserve(dim_ * pts.size());
      for (std::size_t i = 0; i < pts.size(); ++i)
        points_cache.insert(points_cache.end(), construct_it(ptstmp[i]), construct_it(ptstmp[i], 0));
    }

    for(std::size_t i = 0; i < leaf_nodes.size(); ++i){
      std::ptrdiff_t tmp = leaf_nodes[i].begin() - pts.begin();
      leaf_nodes[i].data = ptstmp.begin() + tmp;
    }
    pts.swap(ptstmp);

    data.clear();
    data.shrink_to_fit();

    built_ = true;
  }

  // Only correct when build() has been called
  int dim() const
  {
    return dim_;
  }

  std::ostream&
  write_graphviz(std::ostream& s) const
  {
    int counter = -1;
    std::unordered_map<const Node*, int> node_to_index;
    tree_root->get_indices(counter, node_to_index);

    const auto node_name = [&](const Node* node) {
      const int index = node_to_index.at(node);
      std::string node_name = "default_name";
      if (node->is_leaf()) { // leaf node
        node_name = "L" + std::to_string(index);
      } else {
        if (index == 0) { // root node
          node_name = "R" + std::to_string(index);
        } else { // internal node
          node_name = "N" + std::to_string(index);
        }
      }
      CGAL_assertion(node_name != "default_name");
      return node_name;
    };

    s << "graph G" << std::endl;
    s << "{" << std::endl << std::endl;
    s << "label=\"Graph G. Num leaves: " << tree_root->num_nodes() << ". ";
    s << "Num items: " << tree_root->num_items() << ".\"" << std::endl;
    s << node_name(tree_root) + " ;";
    tree_root->print(s, node_name);
    s << std::endl << "}" << std::endl << std::endl;
    return s;
  }

private:
  //any call to this function is for the moment not threadsafe
  void const_build() const {
    #ifdef CGAL_HAS_THREADS
    //this ensure that build() will be called once
    CGAL_SCOPED_LOCK(building_mutex);
    if(!is_built())
    #endif
      const_cast<Self*>(this)->build(); //THIS IS NOT THREADSAFE
  }
public:

  bool is_built() const
  {
    return built_;
  }

  void invalidate_build()
  {
    if(removed_!=0){
      // Walk the tree to collect the remaining points.
      // Writing directly to pts would likely work, but better be safe.
      std::vector<Point_d> ptstmp;
      //ptstmp.resize(root()->num_items());
      root()->tree_items(std::back_inserter(ptstmp));
      pts.swap(ptstmp);
      removed_=0;
      CGAL_assertion(is_built()); // the rest of the cleanup must happen
    }
    if(is_built()){
      internal_nodes.clear();
      leaf_nodes.clear();
      data.clear();
      delete bbox;
      built_ = false;
    }
  }

  void clear()
  {
    invalidate_build();
    pts.clear();
    removed_ = 0;
  }

  void
  insert(const Point_d& p)
  {
    invalidate_build();
    pts.push_back(p);
  }

  template <class InputIterator>
  void
  insert(InputIterator first, InputIterator beyond)
  {
    invalidate_build();
    pts.insert(pts.end(),first, beyond);
  }

private:
  struct Equal_by_coordinates {
    SearchTraits const* traits;
    Point_d const* pp;
    bool operator()(Point_d const&q) const {
      typename SearchTraits::Construct_cartesian_const_iterator_d ccci=traits->construct_cartesian_const_iterator_d_object();
      return std::equal(ccci(*pp), ccci(*pp,0), ccci(q));
    }
  };
  Equal_by_coordinates equal_by_coordinates(Point_d const&p){
    Equal_by_coordinates ret = { &traits(), &p };
    return ret;
  }

public:
  void
  remove(const Point_d& p)
  {
    remove(p, equal_by_coordinates(p));
  }

  template<class Equal>
  void
  remove(const Point_d& p, Equal const& equal_to_p)
  {
#if 0
    // This code could have quadratic runtime.
    if (!is_built()) {
      std::vector<Point_d>::iterator pi = std::find_if(pts.begin(), pts.end(), equal_to_p);
      // Precondition: the point must be there.
      CGAL_assertion (pi != pts.end());
      pts.erase(pi);
      return;
    }
#endif
    bool success = remove_(p, 0, false, 0, false, root(), equal_to_p);
    CGAL_assertion(success);

    // Do not set the flag is the tree has been cleared.
    if(is_built() && success)
      ++removed_;
  }
private:
  template<class Equal>
  bool remove_(const Point_d& p,
      Internal_node_handle grandparent, bool parent_islower,
      Internal_node_handle parent, bool islower,
      Node_handle node, Equal const& equal_to_p) {
    // Recurse to locate the point
    if (!node->is_leaf()) {
      Internal_node_handle newparent = static_cast<Internal_node_handle>(node);
      // FIXME: This should be if(x<y) remove low; else remove up;
      if (traits().construct_cartesian_const_iterator_d_object()(p)[newparent->cutting_dimension()] <= newparent->cutting_value()) {
        if (remove_(p, parent, islower, newparent, true, newparent->lower(), equal_to_p))
          return true;
      }
      //if (traits().construct_cartesian_const_iterator_d_object()(p)[newparent->cutting_dimension()] >= newparent->cutting_value())
        return remove_(p, parent, islower, newparent, false, newparent->upper(), equal_to_p);

    }

    // Actual removal
    Leaf_node_handle lnode = static_cast<Leaf_node_handle>(node);
    if (lnode->size() > 1) {
      iterator pi = std::find_if(lnode->begin(), lnode->end(), equal_to_p);
      // FIXME: we should ensure this never happens
      if (pi == lnode->end()) return false;
      iterator lasti = lnode->end() - 1;
      if (pi != lasti) {
        // Hack to get a non-const iterator
        std::iter_swap(pts.begin()+(pi-pts.begin()), pts.begin()+(lasti-pts.begin()));
      }
      lnode->drop_last_point();
    } else if (!equal_to_p(*lnode->begin())) {
      // FIXME: we should ensure this never happens
      return false;
    } else if (grandparent) {
      Node_handle brother = islower ? parent->upper() : parent->lower();
      if (parent_islower)
        grandparent->set_lower(brother);
      else
        grandparent->set_upper(brother);
    } else if (parent) {
      tree_root = islower ? parent->upper() : parent->lower();
    } else {
      clear();
    }
    return true;
  }

public:
  //For efficiency; reserve the size of the points vectors in advance (if the number of points is already known).
  void reserve(size_t size)
  {
    pts.reserve(size);
  }

  //Get the capacity of the underlying points vector.
  size_t capacity()
  {
    return pts.capacity();
  }


  template <class OutputIterator, class FuzzyQueryItem>
  OutputIterator
  search(OutputIterator it, const FuzzyQueryItem& q) const
  {
    if(! pts.empty()){

      if(! is_built()){
        const_build();
      }
      Kd_tree_rectangle<FT,D> b(*bbox);
      return tree_root->search(it,q,b,begin(),cache_begin(),dim_);
    }
    return it;
  }


  template <class FuzzyQueryItem>
  std::optional<Point_d>
  search_any_point(const FuzzyQueryItem& q) const
  {
    if(! pts.empty()){

      if(! is_built()){
        const_build();
      }
      Kd_tree_rectangle<FT,D> b(*bbox);
      return tree_root->search_any_point(q,b,begin(),cache_begin(),dim_);
    }
    return std::nullopt;
  }


  ~Kd_tree() {
    if(is_built()){
      delete bbox;
    }
  }


  const SearchTraits&
  traits() const
  {
    return traits_;
  }

  Node_const_handle
  root() const
  {
    if(! is_built()){
      const_build();
    }
    return tree_root;
  }

  Node_handle
  root()
  {
    if(! is_built()){
      build();
    }
    return tree_root;
  }

  void
  print() const
  {
    if(! pts.empty()){
      if(! is_built()){
        const_build();
      }
      root()->print();
    }else{
      std::cout << "empty tree\n";
    }
  }

  const Kd_tree_rectangle<FT,D>&
  bounding_box() const
  {
    if(! is_built()){
      const_build();
    }
    return *bbox;
  }


  typename std::vector<FT>::const_iterator
    cache_begin() const
  {
    return points_cache.begin();
  }

  const_iterator
  begin() const
  {
    return pts.begin();
  }

  const_iterator
  end() const
  {
    return pts.end();
  }

  size_type
  size() const
  {
    return pts.size()-removed_;
  }

  // Print statistics of the tree.
  std::ostream&
  statistics(std::ostream& s) const
  {
    if(! is_built()){
      const_build();
    }
    s << "Tree statistics:" << std::endl;
    s << "Number of items stored: "
      << root()->num_items() << std::endl;
    s << "Number of nodes: "
      << root()->num_nodes() << std::endl;
    s << " Tree depth: " << root()->depth() << std::endl;
    return s;
  }


};

} // namespace CGAL

#include <CGAL/enable_warnings.h>

#endif // CGAL_KD_TREE_H
