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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:
//
// A comparator that sorts edges by:
// i.   the chain maximum for the upper end of the edge
//          this clusters all edges together that lead to the chain maximum
// ii.  the index of the low end of the edge
//          this sorts the edges for the chain max by the low end
//
// 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_edge_peak_comparator_h
#define vtkm_worklet_contourtree_edge_peak_comparator_h

#include <vtkm/cont/ArrayHandle.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Comparator for edges to sort governing saddles high
template <typename T, typename StorageType, typename DeviceAdapter>
class EdgePeakComparator
{
public:
  using ValuePortalType = typename vtkm::cont::ArrayHandle<T, StorageType>::template ExecutionTypes<
    DeviceAdapter>::PortalConst;
  using IdPortalType =
    typename vtkm::cont::ArrayHandle<vtkm::Id>::template ExecutionTypes<DeviceAdapter>::PortalConst;

  ValuePortalType values;
  IdPortalType valueIndex;
  IdPortalType edgeFar;
  IdPortalType edgeNear;
  IdPortalType arcArray;
  bool isJoinGraph;

  VTKM_CONT
  EdgePeakComparator(ValuePortalType Values,
                     IdPortalType ValueIndex,
                     IdPortalType EdgeFar,
                     IdPortalType EdgeNear,
                     IdPortalType ArcArray,
                     bool IsJoinGraph)
    : values(Values)
    , valueIndex(ValueIndex)
    , edgeFar(EdgeFar)
    , edgeNear(EdgeNear)
    , arcArray(ArcArray)
    , isJoinGraph(IsJoinGraph)
  {
  }

  VTKM_EXEC
  bool operator()(const vtkm::Id& i, const vtkm::Id& j) const
  {
    // first compare the far end
    if (edgeFar.Get(i) < edgeFar.Get(j))
      return true ^ isJoinGraph;
    if (edgeFar.Get(j) < edgeFar.Get(i))
      return false ^ isJoinGraph;

    // the compare the values of the low end
    vtkm::Id valueIndex1 = valueIndex.Get(edgeNear.Get(i));
    vtkm::Id valueIndex2 = valueIndex.Get(edgeNear.Get(j));

    if (values.Get(valueIndex1) < values.Get(valueIndex2))
      return true ^ isJoinGraph;
    if (values.Get(valueIndex2) < values.Get(valueIndex1))
      return false ^ isJoinGraph;

    // finally compare the indices
    if (valueIndex1 < valueIndex2)
      return true ^ isJoinGraph;
    if (valueIndex2 < valueIndex1)
      return false ^ isJoinGraph;

    if (i < j)
      return false ^ isJoinGraph;
    if (j < i)
      return true ^ isJoinGraph;

    // fallback can happen when multiple paths end at same extremum
    return false; //true ^ graph.isJoinGraph;
  }

}; // EdgePeakComparator
}
}
}

#endif
