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#ifndef vtkm_worklet_cosmotools_compute_neighbor_bins_h
#define vtkm_worklet_cosmotools_compute_neighbor_bins_h

#include <vtkm/worklet/WorkletMapField.h>

namespace vtkm
{
namespace worklet
{
namespace cosmotools
{

// Worklet for computing the left neighbor bin id for every particle in domain
// In 3D there will be 9 "left" neighbors which start 3 consecutive bins = 27
class ComputeNeighborBins : public vtkm::worklet::WorkletMapField
{
public:
  using ControlSignature = void(FieldIn<IdType> partIndx,
                                FieldIn<IdType> binId,               // (input) bin Id
                                WholeArrayOut<IdType> leftNeighbor); // (output) neighbor Id
  using ExecutionSignature = void(_1, _2, _3);
  using InputDomain = _1;

  vtkm::Id xNum, yNum, zNum;
  vtkm::Id NUM_NEIGHBORS;

  // Constructor
  VTKM_EXEC_CONT
  ComputeNeighborBins(vtkm::Id XNum, vtkm::Id YNum, vtkm::Id ZNum, vtkm::Id NumNeighbors)
    : xNum(XNum)
    , yNum(YNum)
    , zNum(ZNum)
    , NUM_NEIGHBORS(NumNeighbors)
  {
  }

  template <typename OutFieldPortalType>
  VTKM_EXEC void operator()(const vtkm::Id& i,
                            const vtkm::Id& binId,
                            OutFieldPortalType& leftNeighbor) const
  {
    const vtkm::Id xbin = binId % xNum;
    const vtkm::Id ybin = (binId / xNum) % yNum;
    const vtkm::Id zbin = binId / (xNum * yNum);

    vtkm::Id cnt = 0;
    for (vtkm::Id z = zbin - 1; z <= zbin + 1; z++)
    {
      for (vtkm::Id y = ybin - 1; y <= ybin + 1; y++)
      {
        if ((y >= 0) && (y < yNum) && (z >= 0) && (z < zNum))
        {
          if (xbin - 1 >= 0)
            leftNeighbor.Set((NUM_NEIGHBORS * i + cnt), (xbin - 1) + y * xNum + z * xNum * yNum);
          else
            leftNeighbor.Set((NUM_NEIGHBORS * i + cnt), xbin + y * xNum + z * xNum * yNum);
        }
        else
        {
          leftNeighbor.Set((NUM_NEIGHBORS * i + cnt), -1);
        }
        cnt++;
      }
    }
  }
}; // ComputeNeighborBins
}
}
}

#endif
