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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:
//
// This functor identifies for each vertex which edges to keep. For arbitrary meshes,
// this should use reductions. For regular meshes, this way is faster due to low bounded
// updegree.
//
// 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 ()
//
// Vectors marked I/O are intrinsically risky unless there is an algorithmic guarantee
// that the read/writes are completely independent - which for our case actually occurs
// The I/O vectors should therefore be justified in comments both here & in caller
//
//=======================================================================================

#ifndef vtkm_worklet_contourtree_join_tree_transferrer_h
#define vtkm_worklet_contourtree_join_tree_transferrer_h

#include <vtkm/worklet/WorkletMapField.h>
#include <vtkm/worklet/contourtree/Types.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Worklet for setting initial chain maximum value
class JoinTreeTransferrer : public vtkm::worklet::WorkletMapField
{
public:
  typedef void ControlSignature(
    FieldIn<IdType> vertex,            // (input) index into active vertices
    FieldIn<IdType> prunesTo,          // (input) where vertex is pruned to
    WholeArrayIn<IdType> valueIndex,   // (input) indices into main array
    WholeArrayIn<IdType> chainExtemum, // (input) chain extemum for vertices
    WholeArrayOut<IdType> saddles,     // (output) saddle array for writing
    WholeArrayOut<IdType> arcArray);   // (output) arc / max array for writing
  typedef void ExecutionSignature(_1, _2, _3, _4, _5, _6);
  using InputDomain = _1;

  // Constructor
  VTKM_EXEC_CONT
  JoinTreeTransferrer() {}

  template <typename InFieldPortalType, typename OutFieldPortalType>
  VTKM_EXEC void operator()(const vtkm::Id& vertex,
                            const vtkm::Id& prunesTo,
                            const InFieldPortalType& valueIndex,
                            const InFieldPortalType& chainExtremum,
                            const OutFieldPortalType& saddles,
                            const OutFieldPortalType& arcArray) const
  {
    // convert vertex & prunesTo to indices in original data
    // and write to saddle array
    if (prunesTo == NO_VERTEX_ASSIGNED)
      saddles.Set(valueIndex.Get(vertex), NO_VERTEX_ASSIGNED);
    else
      saddles.Set(valueIndex.Get(vertex), valueIndex.Get(prunesTo));
    // and in either event, we need to transfer the chain maximum
    arcArray.Set(valueIndex.Get(vertex), valueIndex.Get(chainExtremum.Get(vertex)));
  }
}; // JoinTreeTransferrer
}
}
}

#endif