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#ifndef vtkm_worklet_cosmotools_compute_potential_neighbors_h
#define vtkm_worklet_cosmotools_compute_potential_neighbors_h

#include <vtkm/worklet/WorkletMapField.h>

namespace vtkm
{
namespace worklet
{
namespace cosmotools
{

// Worklet for computing the potential for a particle using 27 neighbor bins
template <typename T>
class ComputePotentialNeighbors : public vtkm::worklet::WorkletMapField
{
public:
  using TagType = vtkm::List<T>;

  using ControlSignature = void(FieldIn index,                // (input) particle Id
                                WholeArrayIn binId,           // (input) bin id for this particle
                                WholeArrayIn partId,          // (input) first particle in halo
                                WholeArrayIn xLoc,            // (input) x location in domain
                                WholeArrayIn yLoc,            // (input) y location in domain
                                WholeArrayIn zLoc,            // (input) z location in domain
                                WholeArrayIn firstParticleId, // (input) first particle in halo
                                WholeArrayIn lastParticleId,  // (input) last particle in halo
                                FieldOut potential);          // (output) bin ID
  using ExecutionSignature = _9(_1, _2, _3, _4, _5, _6, _7, _8);
  using InputDomain = _1;

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

  // Constructor
  VTKM_EXEC_CONT
  ComputePotentialNeighbors(const vtkm::Id XNum,
                            const vtkm::Id YNum,
                            const vtkm::Id ZNum,
                            const vtkm::Id NumNeighbors,
                            T Mass)
    : xNum(XNum)
    , yNum(YNum)
    , zNum(ZNum)
    , NUM_NEIGHBORS(NumNeighbors)
    , mass(Mass)
  {
  }

  template <typename InFieldPortalType, typename InIdPortalType, typename InVectorPortalType>
  VTKM_EXEC T operator()(const vtkm::Id& i,
                         const InIdPortalType& binId,
                         const InIdPortalType& partId,
                         const InFieldPortalType& xLoc,
                         const InFieldPortalType& yLoc,
                         const InFieldPortalType& zLoc,
                         const InVectorPortalType& firstParticleId,
                         const InVectorPortalType& lastParticleId) const
  {
    vtkm::Id iId = partId.Get(i);
    vtkm::Id ibin = binId.Get(i);

    const vtkm::Id yVal = (ibin / xNum) % yNum;
    const vtkm::Id zVal = ibin / (xNum * yNum);
    vtkm::Id cnt = 0;
    T potential = 0.0f;

    // Iterate on the 9 sets of neighbor particles
    for (vtkm::Id z = zVal - 1; z <= zVal + 1; z++)
    {
      for (vtkm::Id y = yVal - 1; y <= yVal + 1; y++)
      {
        vtkm::Id firstBinId = NUM_NEIGHBORS * i + cnt;
        vtkm::Id startParticle = firstParticleId.Get(firstBinId);
        vtkm::Id endParticle = lastParticleId.Get(firstBinId);

        for (vtkm::Id j = startParticle; j < endParticle; j++)
        {
          vtkm::Id jId = partId.Get(j);
          T xDist = xLoc.Get(iId) - xLoc.Get(jId);
          T yDist = yLoc.Get(iId) - yLoc.Get(jId);
          T zDist = zLoc.Get(iId) - zLoc.Get(jId);
          T r = vtkm::Sqrt((xDist * xDist) + (yDist * yDist) + (zDist * zDist));
          if ((i != j) && (fabs(r) > 0.00000000001f))
            potential -= mass / r;
        }
        cnt++;
      }
    }
    return potential;
  }
}; // ComputePotentialNeighbors
}
}
}

#endif
