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#ifndef vtkm_worklet_cosmotools_mark_active_neighbors_h
#define vtkm_worklet_cosmotools_mark_active_neighbors_h

#include <vtkm/exec/ExecutionWholeArray.h>
#include <vtkm/worklet/WorkletMapField.h>

namespace vtkm
{
namespace worklet
{
namespace cosmotools
{

// Worklet for particles to indicate which neighbors are active
// because at least one particle in that bin is within linking length
template <typename T>
class MarkActiveNeighbors : public vtkm::worklet::WorkletMapField
{
public:
  struct TagType : vtkm::ListTagBase<T>
  {
  };

  typedef void ControlSignature(
    FieldIn<IdType> index,            // (input) particle index
    FieldIn<IdType> partId,           // (input) particle id sorted
    FieldIn<IdType> binId,            // (input) bin Id per particle
    WholeArrayIn<IdType> partIdArray, // (input) sequence imposed on sorted particle Ids
    WholeArrayIn<TagType> location,   // (input) location of particles
    WholeArrayIn<IdType> firstPartId, // (input) vector of first particle indices
    WholeArrayIn<IdType> lastPartId,  // (input) vector of last particle indices
    FieldOut<vtkm::UInt32> flag);     // (output) active bin neighbors mask
  typedef _8 ExecutionSignature(_1, _2, _3, _4, _5, _6, _7);
  typedef _1 InputDomain;

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

  // Constructor
  VTKM_EXEC_CONT
  MarkActiveNeighbors(const vtkm::Id XNum,
                      const vtkm::Id YNum,
                      const vtkm::Id ZNum,
                      const vtkm::Id NumNeighbors,
                      const T LinkLen)
    : xNum(XNum)
    , yNum(YNum)
    , zNum(ZNum)
    , NUM_NEIGHBORS(NumNeighbors)
    , linkLenSq(LinkLen * LinkLen)
  {
  }

  template <typename InIdPortalType, typename InFieldPortalType, typename InVectorPortalType>
  VTKM_EXEC vtkm::UInt32 operator()(const vtkm::Id& i,
                                    const vtkm::Id& iPartId,
                                    const vtkm::Id& iBinId,
                                    const InIdPortalType& partIdArray,
                                    const InFieldPortalType& location,
                                    const InVectorPortalType& firstPartId,
                                    const InVectorPortalType& lastPartId) const
  {
    const vtkm::Id ybin = (iBinId / xNum) % yNum;
    const vtkm::Id zbin = iBinId / (xNum * yNum);
    vtkm::UInt32 activeFlag = 0;
    vtkm::UInt32 bcnt = 1;
    vtkm::Id cnt = 0;

    // Examine all neighbor bins surrounding this particle
    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))
        {
          vtkm::Id pos = NUM_NEIGHBORS * i + cnt;
          vtkm::Id startParticle = firstPartId.Get(pos);
          vtkm::Id endParticle = lastPartId.Get(pos);

          // If the bin has any particles, check to see if any of those
          // are within the linking length from this particle
          for (vtkm::Id j = startParticle; j < endParticle; j++)
          {
            vtkm::Id jPartId = partIdArray.Get(j);
            vtkm::Vec<T, 3> iloc = location.Get(iPartId);
            vtkm::Vec<T, 3> jloc = location.Get(jPartId);
            T xDist = iloc[0] - jloc[0];
            T yDist = iloc[1] - jloc[1];
            T zDist = iloc[2] - jloc[2];

            // Found a particle within linking length so this bin is active
            if ((xDist * xDist + yDist * yDist + zDist * zDist) <= linkLenSq)
            {
              activeFlag = activeFlag | bcnt;
              break;
            }
          }
        }
        bcnt = bcnt << 1;
        cnt++;
      }
    }
    return activeFlag;
  }
}; // MarkActiveNeighbors
}
}
}

#endif
