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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>
#include <vtkm/cont/ExecutionObjectBase.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Comparator for edges to sort governing saddles high
template <typename T, typename StorageType>
class EdgePeakComparator : public vtkm::cont::ExecutionObjectBase
{
public:
  using ValueArrayType = vtkm::cont::ArrayHandle<T, StorageType>;
  using IdArrayType = vtkm::cont::ArrayHandle<vtkm::Id>;

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

  ValueArrayType Values;
  IdArrayType ValueIndex;
  IdArrayType EdgeFar;
  IdArrayType EdgeNear;
  IdArrayType ArcArray;
  bool IsJoinGraph;

  class ExecObject
  {
  public:
    using ValuePortalType = typename ValueArrayType::ReadPortalType;
    using IdPortalType = typename IdArrayType::ReadPortalType;

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

    ValuePortalType Values;
    IdPortalType ValueIndex;
    IdPortalType EdgeFar;
    IdPortalType EdgeNear;
    IdPortalType ArcArray;
    bool IsJoinGraph;

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

      // the compare the values of the low end
      vtkm::Id valueIndex1 = this->ValueIndex.Get(this->EdgeNear.Get(i));
      vtkm::Id valueIndex2 = this->ValueIndex.Get(this->EdgeNear.Get(j));

      if (this->Values.Get(valueIndex1) < this->Values.Get(valueIndex2))
        return true ^ this->IsJoinGraph;
      if (this->Values.Get(valueIndex2) < this->Values.Get(valueIndex1))
        return false ^ this->IsJoinGraph;

      // finally compare the indices
      if (valueIndex1 < valueIndex2)
        return true ^ this->IsJoinGraph;
      if (valueIndex2 < valueIndex1)
        return false ^ this->IsJoinGraph;

      if (i < j)
        return false ^ this->IsJoinGraph;
      if (j < i)
        return true ^ this->IsJoinGraph;

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

  VTKM_CONT ExecObject PrepareForExecution(vtkm::cont::DeviceAdapterId device,
                                           vtkm::cont::Token& token) const
  {
    return ExecObject(this->Values.PrepareForInput(device, token),
                      this->ValueIndex.PrepareForInput(device, token),
                      this->EdgeFar.PrepareForInput(device, token),
                      this->EdgeNear.PrepareForInput(device, token),
                      this->ArcArray.PrepareForInput(device, token),
                      this->IsJoinGraph);
  }
}; // EdgePeakComparator
}
}
}

#endif
