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//
// Copyright (c) 2005-2024, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
//
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// This file is part of FastJet.
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#ifndef DROP_CGAL // in case we do not have the code for CGAL
#ifndef __FASTJET_DNN3PICYLINDER_HH__
#define __FASTJET_DNN3PICYLINDER_HH__

#include "fastjet/internal/DynamicNearestNeighbours.hh"
#include "fastjet/internal/DnnPlane.hh"
#include "fastjet/internal/numconsts.hh"

FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh

/// \if internal_doc
/// @ingroup internal
/// \class Dnn3piCylinder
/// class derived from DynamicNearestNeighbours that provides an
/// implementation for the surface of cylinder (using one 
/// DnnPlane object spanning 0--3pi).
/// \endif
class Dnn3piCylinder : public DynamicNearestNeighbours {
 public:
  /// empty initaliser
  Dnn3piCylinder() {}

  /// Initialiser from a set of points on an Eta-Phi plane, where
  /// eta can have an arbitrary ranges and phi must be in range
  /// 0 <= phi < 2pi;
  /// 
  /// NB: this class is more efficient than the plain Dnn4piCylinder
  /// class, but can give wrong answers when the nearest neighbour is
  /// further away than 2pi (in this case a point's nearest neighbour
  /// becomes itself, because it is considered to be a distance 2pi
  /// away). For the kt-algorithm (e.g.) this is actually not a
  /// problem (the distance need only be accurate when it is less than
  /// R), so we can tell the routine to ignore this problem --
  /// alternatively the routine will crash if it detects it occurring
  /// (only when finding the nearest neighbour index, not its
  /// distance).
  Dnn3piCylinder(const std::vector<EtaPhi> &,
		 const bool & ignore_nearest_is_mirror = false,
		 const bool & verbose = false );

  /// Returns the index of  the nearest neighbour of point labelled
  /// by ii (assumes ii is valid)
  int NearestNeighbourIndex(const int ii) const ;

  /// Returns the distance to the nearest neighbour of point labelled
  /// by index ii (assumes ii is valid)
  double NearestNeighbourDistance(const int ii) const ;

  /// Returns true iff the given index corresponds to a point that
  /// exists in the DNN structure (meaning that it has been added, and
  /// not removed in the meantime)
  bool Valid(const int index) const;

  void RemoveAndAddPoints(const std::vector<int> & indices_to_remove,
			  const std::vector<EtaPhi> & points_to_add,
			  std::vector<int> & indices_added,
			  std::vector<int> & indices_of_updated_neighbours);

  ~Dnn3piCylinder();

 private:

  // our extras to help us navigate, find distance, etc.
  const static int INEXISTENT_VERTEX=-3;

  bool _verbose;

  bool _ignore_nearest_is_mirror;

  /// Picture of how things will work... Copy 0--pi part of the 0--2pi
  /// cylinder into a region 2pi--3pi of a Euclidean plane. Below we
  /// show points labelled by + that have a mirror image in this
  /// manner, while points labelled by * do not have a mirror image.
  ///      	 			  
  ///      |           .     |		  
  ///      |	       .     |		  
  ///      |           .     |		  
  ///      |           .     |		  
  ///      |        2  .     |		  
  ///      |        *  .     |		  
  ///      | +         . +   |		  
  ///      | 0         . 1   |
  ///      |	       .     |
  ///      0          2pi   3pi
  ///   	     
  /// Each "true" point has its true "cylinder" index (the index that
  /// is known externally to this class) as well as euclidean plane
  /// indices (main_index and mirror index in the MirrorVertexInfo
  /// structure), which are private concepts of this class.
  /// 
  /// In above picture our structures would hold the following info
  /// (the picture shows the euclidean-plane numbering)
  ///
  /// _mirror_info[cylinder_index = 0] = (0, 1)
  /// _mirror_info[cylinder_index = 1] = (2, INEXISTENT_VERTEX)
  ///
  /// We also need to be able to go from the euclidean plane indices
  /// back to the "true" cylinder index, and for this purpose we use
  /// the vector _cylinder_index_of_plane_vertex[...], which in the above example has
  /// the following contents
  ///
  /// _cylinder_index_of_plane_vertex[0] = 0
  /// _cylinder_index_of_plane_vertex[1] = 0
  /// _cylinder_index_of_plane_vertex[2] = 1
  ///

  /// 
  struct MirrorVertexInfo {
    /// index of the given point (appearing in the range 0--2pi) in the 
    /// 0--3pi euclidean plane structure (position will coincide with
    /// that on the 0--2pi cylinder, but index labelling it will be
    /// different)
    int main_index; 
    /// index of the mirror point (appearing in the range 2pi--3pi) in the
    /// 0--3pi euclidean plane structure
    int mirror_index; 
  };

  // for each "true" vertex we have reference to indices in the euclidean
  // plane structure
  std::vector<MirrorVertexInfo> _mirror_info;
  // for each index in the euclidean 0--3pi plane structure we want to
  // be able to get back to the "true" vertex index on the overall
  // 0--2pi cylinder structure
  std::vector<int> _cylinder_index_of_plane_vertex;

  // NB: we define POINTERS here because the initialisation gave
  //     us problems (things crashed!), perhaps because in practice
  //     we were making a copy without being careful and defining
  //     a proper copy constructor.
  DnnPlane * _DNN;

  /// given a phi value in the 0--2pi range return one 
  /// in the pi--3pi range.
  inline EtaPhi _remap_phi(const EtaPhi & point) {
    double phi = point.second;
    if (phi < pi) { phi += twopi ;}
    return EtaPhi(point.first, phi);}


  //----------------------------------------------------------------------
  /// What on earth does this do?
  ///
  /// Example: last true "cylinder" index was 15
  ///          last plane index was 23
  /// 
  /// Then: _cylinder_index_of_plane_vertex.size() = 24 and 
  ///       _mirror_info.size() = 16
  ///
  /// IF cylinder_point's phi < pi then
  ///   create:  _mirror_info[16] = (main_index = 24, mirror_index=25) 
  ///            _cylinder_index_of_plane_vertex[24] = 16
  ///            _cylinder_index_of_plane_vertex[25] = 16
  /// ELSE
  ///  create: _mirror_info[16] = (main_index = 24, mirror_index=INEXISTENT..) 
  ///          _cylinder_index_of_plane_vertex[24] = 16
  ///
  /// ADDITIONALLY push the cylinder_point (and if it exists the mirror
  /// copy) onto the vector plane_points.
  void _RegisterCylinderPoint (const EtaPhi & cylinder_point,
			       std::vector<EtaPhi> & plane_points);
};


// here follow some inline implementations of the simpler of the
// functions defined above

//----------------------------------------------------------------------
/// Note: one of the difficulties of the 0--3pi mapping is that
/// a point may have its mirror copy as its own nearest neighbour
/// (if no other point is within a distance of 2pi). This does
/// not matter for the kt_algorithm with
/// reasonable values of radius, but might matter for a general use
/// of this algorithm -- depending on whether or not the user has
/// initialised the class with instructions to ignore this problem the
/// program will detect and ignore it, or crash.
inline int Dnn3piCylinder::NearestNeighbourIndex(const int current) const {
  int main_index = _mirror_info[current].main_index;
  int mirror_index = _mirror_info[current].mirror_index;
  int plane_index;
  if (mirror_index == INEXISTENT_VERTEX ) {
    plane_index = _DNN->NearestNeighbourIndex(main_index);
  } else {
    plane_index = (
	_DNN->NearestNeighbourDistance(main_index) < 
	_DNN->NearestNeighbourDistance(mirror_index)) ? 
      _DNN->NearestNeighbourIndex(main_index) : 
      _DNN->NearestNeighbourIndex(mirror_index) ; 
  }
  int this_cylinder_index = _cylinder_index_of_plane_vertex[plane_index];
  // either the user has acknowledged the fact that they may get the
  // mirror copy as the closest point, or crash if it should occur
  // that mirror copy is the closest point.
  assert(_ignore_nearest_is_mirror || this_cylinder_index != current);
  //if (this_cylinder_index == current) {
  //  std::cerr << "WARNING point "<<current<<
  //    " has its mirror copy as its own nearest neighbour"<<endl;
  //}
  return this_cylinder_index;
}

inline double Dnn3piCylinder::NearestNeighbourDistance(const int current) const {
  int main_index = _mirror_info[current].main_index;
  int mirror_index = _mirror_info[current].mirror_index;
  if (mirror_index == INEXISTENT_VERTEX ) {
    return _DNN->NearestNeighbourDistance(main_index);
  } else {
    return (
	_DNN->NearestNeighbourDistance(main_index) < 
	_DNN->NearestNeighbourDistance(mirror_index)) ? 
      _DNN->NearestNeighbourDistance(main_index) : 
      _DNN->NearestNeighbourDistance(mirror_index) ; 
  }
 
}

inline bool Dnn3piCylinder::Valid(const int index) const {
  return (_DNN->Valid(_mirror_info[index].main_index));
}


inline Dnn3piCylinder::~Dnn3piCylinder() {
  delete _DNN; 
}


FASTJET_END_NAMESPACE

#endif //  __FASTJET_DNN3PICYLINDER_HH__
#endif //  DROP_CGAL 
