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//  Copyright 2014 National Technology & Engineering Solutions of Sandia, LLC (NTESS).
//  Copyright 2014 UT-Battelle, LLC.
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//  this software.
//============================================================================
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//============================================================================

//  This code is based on the algorithm presented in the paper:
//  “Parallel Peak Pruning for Scalable SMP Contour Tree Computation.”
//  Hamish Carr, Gunther Weber, Christopher Sewell, and James Ahrens.
//  Proceedings of the IEEE Symposium on Large Data Analysis and Visualization
//  (LDAV), October 2016, Baltimore, Maryland.

//=======================================================================================
//
// COMMENTS:
//
// Basically, we have a single functor (so far), whose job is to work out the downwards
// join neighbour of each vertex.
//
// Any vector needed by the functor for lookup purposes will be passed as a parameter to
// the constructor and saved, with the actual function call being the operator ()
//
//=======================================================================================

#ifndef vtkm_worklet_contourtree_vertex_merge_comparator_h
#define vtkm_worklet_contourtree_vertex_merge_comparator_h

#include <vtkm/cont/ArrayHandle.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

//=======================================================================================
//
//	VertexMergeComparator
//
// A comparator that sorts the vertices on the join maximum (assuming already sorted on
// indexed value)
//
//=======================================================================================

template <typename T, typename StorageType, typename DeviceAdapter>
class VertexMergeComparator
{
public:
  typedef typename vtkm::cont::ArrayHandle<T, StorageType>::template ExecutionTypes<
    DeviceAdapter>::PortalConst ValuePortalType;
  typedef
    typename vtkm::cont::ArrayHandle<vtkm::Id>::template ExecutionTypes<DeviceAdapter>::PortalConst
      IdPortalType;

  ValuePortalType values;
  IdPortalType extrema;
  bool isJoinTree;

  VTKM_EXEC_CONT
  VertexMergeComparator(ValuePortalType Values, IdPortalType Extrema, bool IsJoinTree)
    : values(Values)
    , extrema(Extrema)
    , isJoinTree(IsJoinTree)
  {
  }

  VTKM_EXEC
  bool operator()(const vtkm::Id& i, const vtkm::Id& j) const
  {
    // retrieve the pseudo-extremum the vertex belongs to
    vtkm::Id pseudoExtI = extrema.Get(i);
    vtkm::Id pseudoExtJ = extrema.Get(j);

    if (pseudoExtI < pseudoExtJ)
      return false ^ isJoinTree;
    if (pseudoExtJ < pseudoExtI)
      return true ^ isJoinTree;

    T valueI = values.Get(i);
    T valueJ = values.Get(j);

    if (valueI < valueJ)
      return false ^ isJoinTree;
    if (valueI > valueJ)
      return true ^ isJoinTree;
    if (i < j)
      return false ^ isJoinTree;
    if (j < i)
      return true ^ isJoinTree;
    return false; // true ^ isJoinTree;
  }
}; // VertexMergeComparator
}
}
}

#endif
