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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 replaces a parallel loop examining neighbours - again, for arbitrary
// meshes, it needs to be a reduction, but for regular meshes, it's faster this way.
//
// 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_mesh2d_dem_vertex_outdegree_starter_h
#define vtkm_worklet_contourtree_mesh2d_dem_vertex_outdegree_starter_h

#include <vtkm/worklet/WorkletMapField.h>
#include <vtkm/worklet/contourtree/Mesh2D_DEM_Triangulation_Macros.h>

namespace vtkm
{
namespace worklet
{
namespace contourtree
{

// Worklet for setting initial chain maximum value
class Mesh2D_DEM_VertexOutdegreeStarter : public vtkm::worklet::WorkletMapField
{
public:
  using ControlSignature = void(FieldIn vertex,        // (input) index into active vertices
                                FieldIn nbrMask,       // (input) neighbor mask
                                WholeArrayIn arcArray, // (input) chain extrema
                                FieldOut outdegree,    // (output) outdegree
                                FieldOut isCritical);  // (output) whether critical
  using ExecutionSignature = void(_1, _2, _3, _4, _5 /*, _6*/);
  using InputDomain = _1;

  vtkm::Id nRows; // (input) number of rows in 2D
  vtkm::Id nCols; // (input) number of cols in 2D
  bool ascending; // (input) ascending or descending (join or split tree)

  // Constructor
  VTKM_EXEC_CONT
  Mesh2D_DEM_VertexOutdegreeStarter(vtkm::Id NRows, vtkm::Id NCols, bool Ascending)
    : nRows(NRows)
    , nCols(NCols)
    , ascending(Ascending)
  {
  }

  //template<typename InFieldPortalType>
  template <typename InFieldPortalType /*, typename InOutFieldPortalType*/>
  VTKM_EXEC void operator()(const vtkm::Id& vertex,
                            const vtkm::Id& nbrMask,
                            const InFieldPortalType& arcArray,
                            vtkm::Id& outdegree,
                            vtkm::Id& isCritical) const
  {
    // get the row and column
    vtkm::Id row = VERTEX_ROW(vertex, nCols);
    vtkm::Id col = VERTEX_COL(vertex, nCols);

    // we know which edges are outbound, so we count to get the outdegree
    vtkm::Id outDegree = 0;

    vtkm::Id farEnds[MAX_OUTDEGREE];

    // special case for local extremum
    if (nbrMask == 0x3F)
    {
      outDegree = 1;
    }
    else
    { // not a local minimum
      if ((nbrMask & 0x30) == 0x20)
        farEnds[outDegree++] = arcArray.Get(VERTEX_ID(row - 1, col, nCols));
      if ((nbrMask & 0x18) == 0x10)
        farEnds[outDegree++] = arcArray.Get(VERTEX_ID(row - 1, col - 1, nCols));
      if ((nbrMask & 0x0C) == 0x08)
        farEnds[outDegree++] = arcArray.Get(VERTEX_ID(row, col - 1, nCols));
      if ((nbrMask & 0x06) == 0x04)
        farEnds[outDegree++] = arcArray.Get(VERTEX_ID(row + 1, col, nCols));
      if ((nbrMask & 0x03) == 0x02)
        farEnds[outDegree++] = arcArray.Get(VERTEX_ID(row + 1, col + 1, nCols));
      if ((nbrMask & 0x21) == 0x01)
        farEnds[outDegree++] = arcArray.Get(VERTEX_ID(row, col + 1, nCols));
    } // not a local minimum

    // now we check them against each other
    if ((outDegree == 2) && (farEnds[0] == farEnds[1]))
    { // outDegree 2 & both match
      // treat as a regular point
      outDegree = 1;
    } // outDegree 2 & both match
    else if (outDegree == 3)
    { // outDegree 3
      if (farEnds[0] == farEnds[1])
      { // first two match
        if (farEnds[0] == farEnds[2])
        { // triple match
          // all match - treat as regular point
          outDegree = 1;
        } // triple match
        else
        { // first two match, but not third
          // copy third down one place
          farEnds[1] = farEnds[2];
          // and reset the count
          outDegree = 2;
        } //
      }   // first two match
      else if ((farEnds[0] == farEnds[2]) || (farEnds[1] == farEnds[2]))
      { // second one matches either of the first two
        // decrease the count, keeping 0 & 1
        outDegree = 2;
      } // second one matches either of the first two
    }   // outDegree 3

    // now store the outDegree
    outdegree = outDegree;

    // and set the initial inverse index to a flag
    isCritical = (outDegree != 1) ? 1 : 0;
  }
}; // Mesh2D_DEM_VertexOutdegreeStarter

} // namespace contourtree
} // namespace worklet
} // namespace vtkm

#endif
