/*=========================================================================

  Program:   Visualization Toolkit
  Module:    vtkStructuredImplicitConnectivity.h

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notice for more information.

=========================================================================*/
#include "vtkStructuredImplicitConnectivity.h"

// VTK includes
#include "vtkDataArray.h"
#include "vtkFieldDataSerializer.h"
#include "vtkImageData.h"
#include "vtkMPIController.h"
#include "vtkMultiProcessController.h"
#include "vtkMultiProcessStream.h"
#include "vtkObjectFactory.h"
#include "vtkPointData.h"
#include "vtkPoints.h"
#include "vtkRectilinearGrid.h"
#include "vtkStructuredData.h"
#include "vtkStructuredExtent.h"
#include "vtkStructuredGrid.h"

// C/C++ includes
#include <algorithm>
#include <cassert>
#include <map>
#include <sstream>
#include <vector>

//==============================================================================
// INTERNAL DATASTRUCTURES & DEFINITIONS
//==============================================================================

// Some useful extent macros
#define IMIN(ext) ext[0]
#define IMAX(ext) ext[1]
#define JMIN(ext) ext[2]
#define JMAX(ext) ext[3]
#define KMIN(ext) ext[4]
#define KMAX(ext) ext[5]

#define I(ijk) ijk[0]
#define J(ijk) ijk[1]
#define K(ijk) ijk[2]

namespace vtk
{
namespace detail
{

// Given two intervals A=[a1,a2] and B[b1,b2] the IntervalsConnect struct
// enumerates the cases where interval A connects to Interval B.
struct IntervalsConnect
{
  // NOTE: This enum is arranged s.t., negating a value in [-4,4] will yield
  // the mirror inverse
  enum connectivity_t
  {
    IMPLICIT_LO = -4, // Interval A implicitly connects with B on A's low end
    SUBSET = -3,      // Interval A is completely inside interval B
    OVERLAP_LO = -2,  // Interval A intersects with B on A's low end
    LO = -1,          // A's low end touches B's high end A.Low() == B.High()
    ONE_TO_ONE = 0,   // Intervals A,B are exactly the same.
    HI = 1,           // A's high end touches B's low end A.High() == B.Low()
    OVERLAP_HI = 2,   // Interval A intersects with B on A's high end
    SUPERSET = 3,     // Interval A *contains* all of interval B
    IMPLICIT_HI = 4,  // Interval A implicitly connects with B on its high end.

    DISJOINT = 5, // Intervals A,B are completely disjoint.
    UNDEFINED = 6 // Undefined
  };

  static std::string OrientationToString(int orient[3])
  {
    std::ostringstream oss;
    oss << "(";
    for (int i = 0; i < 3; ++i)
    {
      if (i == 1 || i == 2)
      {
        oss << ", ";
      }
      switch (orient[i])
      {
        case IMPLICIT_LO:
          oss << "IMPLICIT_LO";
          break;
        case SUBSET:
          oss << "SUBSET";
          break;
        case OVERLAP_LO:
          oss << "OVERLAP_LO";
          break;
        case LO:
          oss << "LO";
          break;
        case ONE_TO_ONE:
          oss << "ONE_TO_ONE";
          break;
        case HI:
          oss << "HI";
          break;
        case OVERLAP_HI:
          oss << "OVERLAP_HI";
          break;
        case SUPERSET:
          oss << "SUPERSET";
          break;
        case IMPLICIT_HI:
          oss << "IMPLICIT_HI";
          break;
        case DISJOINT:
          oss << "DISJOINT";
          break;
        case UNDEFINED:
          oss << "UNDEFINED";
          break;
        default:
          oss << "*UNKNOWN*";
      } // END switch
    }   // END for
    oss << ")";
    return (oss.str());
  }

}; // END struct IntervalsConnect

//------------------------------------------------------------------------------
//  Interval class Definition
//------------------------------------------------------------------------------
class Interval
{
public:
  Interval()
    : lo(0)
    , hi(-1)
  {
  }
  Interval(const int l, const int h)
    : lo(l)
    , hi(h)
  {
  }
  ~Interval() {}

  int Low() const { return this->lo; }
  int High() const { return this->hi; }
  int Cardinality() const { return (this->hi - this->lo + 1); }
  bool Valid() const { return (this->lo <= this->hi); }
  void Set(const int l, const int h)
  {
    this->lo = l;
    this->hi = h;
  }
  void Invalidate() { this->Set(0, -1); }
  bool Within(const Interval& B) const { return ((this->lo >= B.Low()) && (this->hi <= B.High())); }

  bool ImplicitNeighbor(const Interval& B, int& type);
  static bool ImplicitNeighbors(const Interval& A, const Interval& B, int& type);

  bool Intersects(const Interval& B, Interval& Overlap, int& type);
  static bool Intersects(const Interval& A, const Interval& B, Interval& Overlap, int& type);

private:
  int lo;
  int hi;
};

//------------------------------------------------------------------------------
bool Interval::ImplicitNeighbors(const Interval& A, const Interval& B, int& t)
{
  assert("pre: interval is not valid!" && A.Valid());
  assert("pre: B interval is not valid!" && B.Valid());

  bool status = false;
  if (A.High() + 1 == B.Low())
  {
    status = true;
    t = IntervalsConnect::IMPLICIT_HI;
  }
  else if (B.High() + 1 == A.Low())
  {
    status = true;
    t = IntervalsConnect::IMPLICIT_LO;
  }
  return (status);
}

//------------------------------------------------------------------------------
bool Interval::ImplicitNeighbor(const Interval& B, int& type)
{
  return (Interval::ImplicitNeighbors(*this, B, type));
}

//------------------------------------------------------------------------------
bool Interval::Intersects(const Interval& A, const Interval& B, Interval& Overlap, int& type)
{
  assert("pre: interval is not valid!" && A.Valid());
  assert("pre: B interval is not valid!" && B.Valid());

  bool status = false;

  // Disjoint cases
  if (A.High() < B.Low())
  {
    type = IntervalsConnect::DISJOINT;
    Overlap.Invalidate();
    status = false;
  }
  else if (B.High() < A.Low())
  {
    type = IntervalsConnect::DISJOINT;
    Overlap.Invalidate();
    status = false;
  }
  // ONE_TO_ONE case
  else if (A.Cardinality() == B.Cardinality() && A.Low() == B.Low() && A.High() == B.High())
  {
    type = IntervalsConnect::ONE_TO_ONE;
    Overlap.Set(A.Low(), A.High());
    status = true;
  }
  // A is a SUBSET of B
  else if (A.Within(B))
  {
    type = IntervalsConnect::SUBSET;
    Overlap.Set(A.Low(), A.High());
    status = true;
  }
  // A is a superset of B
  else if (B.Within(A))
  {
    type = IntervalsConnect::SUPERSET;
    Overlap.Set(B.Low(), B.High());
    status = true;
  }
  // A touches B on the high end
  else if (A.High() == B.Low())
  {
    type = IntervalsConnect::HI;
    Overlap.Set(A.High(), A.High());
    status = true;
  }
  // A touches B on the low end
  else if (A.Low() == B.High())
  {
    type = IntervalsConnect::LO;
    Overlap.Set(A.Low(), A.Low());
    status = true;
  }
  // A intersects B on its low end
  else if ((A.Low() >= B.Low()) && (A.Low() <= B.High()))
  {
    type = IntervalsConnect::OVERLAP_LO;
    Overlap.Set(A.Low(), B.High());
    status = true;
  }
  // A intersects B on its high end
  else if ((A.High() >= B.Low()) && (A.High() <= B.High()))
  {
    type = IntervalsConnect::OVERLAP_HI;
    Overlap.Set(B.Low(), A.High());
    status = true;
  }
  else
  {
    vtkGenericWarningMacro(<< "Undefined interval intersection!"
                           << "Code should not reach here!!!");
    type = IntervalsConnect::UNDEFINED;
    status = false;
    Overlap.Invalidate();
  }
  return (status);
}

//------------------------------------------------------------------------------
bool Interval::Intersects(const Interval& B, Interval& Overlap, int& type)
{
  return (Interval::Intersects(*this, B, Overlap, type));
}

//------------------------------------------------------------------------------
struct ImplicitNeighbor
{
  int Rank;           // the rank of the neighbor
  int Extent[6];      // the extent of the neighbor
  int Orientation[3]; // the orientation w.r.t the local extent
  int Overlap[6];     // the overlap extent

  std::string ToString()
  {
    std::ostringstream oss;

    oss << "rank=" << this->Rank << " ";
    oss << "extent=[";
    oss << this->Extent[0] << ", ";
    oss << this->Extent[1] << ", ";
    oss << this->Extent[2] << ", ";
    oss << this->Extent[3] << ", ";
    oss << this->Extent[4] << ", ";
    oss << this->Extent[5] << "] ";
    oss << "overlap=[";
    oss << this->Overlap[0] << ", ";
    oss << this->Overlap[1] << ", ";
    oss << this->Overlap[2] << ", ";
    oss << this->Overlap[3] << ", ";
    oss << this->Overlap[4] << ", ";
    oss << this->Overlap[5] << "] ";
    oss << "orientation=";
    oss << IntervalsConnect::OrientationToString(this->Orientation);

    return (oss.str());
  }
};

//------------------------------------------------------------------------------
struct DomainMetaData
{
  int WholeExtent[6]; // Extent of the entire domain

  int DataDescription; // Data-description of the distributed dataset.
  int NDim;            // Number of dimensions according to DataDescription.
  int DimIndex[3];     // Stores the dimensions of the dataset in the
                       // the right order. This essentially allows to
                       // process 2-D (XY,XZ,YZ) and 3-D datasets in a
                       // transparent way.

  int GlobalImplicit[3]; // indicates for each dimension if there is globally
                         // implicit connectivity. Any value > 0 indicates
                         // implicit connectivity in the given direction.

  // Flat list of extents. Extents are organized as follows:
  // [id, imin, imax, jmin, jmax, kmin, kmax]
  std::vector<int> ExtentListInfo;

  /// \brief Checks if a grid with the given extent is within this domain
  /// \param ext the extent of the grid in query
  /// \return status true if the grid is insided, else false.
  bool HasGrid(int ext[6]) { return (vtkStructuredExtent::Smaller(ext, this->WholeExtent)); }

  /// \brief Initializes the domain metadata.
  void Initialize(int wholeExt[6])
  {
    memcpy(this->WholeExtent, wholeExt, 6 * sizeof(int));
    this->DataDescription = vtkStructuredData::GetDataDescriptionFromExtent(wholeExt);

    if (this->DataDescription == VTK_EMPTY)
    {
      return;
    }

    // Sanity checks!
    assert("pre: data description is VTK_EMPTY!" && (this->DataDescription != VTK_EMPTY));
    assert("pre: dataset must be 2-D or 3-D" && (this->DataDescription >= VTK_XY_PLANE));

    this->NDim = -1;
    std::fill(this->DimIndex, this->DimIndex + 3, -1);
    std::fill(this->GlobalImplicit, this->GlobalImplicit + 3, 0);

    switch (this->DataDescription)
    {
      case VTK_XY_PLANE:
        this->NDim = 2;
        this->DimIndex[0] = 0;
        this->DimIndex[1] = 1;
        break;
      case VTK_XZ_PLANE:
        this->NDim = 2;
        this->DimIndex[0] = 0;
        this->DimIndex[1] = 2;
        break;
      case VTK_YZ_PLANE:
        this->NDim = 2;
        this->DimIndex[0] = 1;
        this->DimIndex[1] = 2;
        break;
      case VTK_XYZ_GRID:
        this->NDim = 3;
        this->DimIndex[0] = 0;
        this->DimIndex[1] = 1;
        this->DimIndex[2] = 2;
        break;
      default:
        vtkGenericWarningMacro(<< "Cannot handle data description: " << this->DataDescription
                               << "\n");
    } // END switch

    assert("post: NDim==2 || NDim==3" && (this->NDim == 2 || this->NDim == 3));
  }
};

//------------------------------------------------------------------------------
struct StructuredGrid
{
  int ID;
  int Extent[6];
  int DataDescription;

  int Grow[3];     // indicates if the grid grows to the right along each dim.
  int Implicit[3]; // indicates implicit connectivity alone each dim.

  vtkPoints* Nodes;
  vtkPointData* PointData;

  // arrays used if the grid is a rectilinear grid
  vtkDataArray* X_Coords;
  vtkDataArray* Y_Coords;
  vtkDataArray* Z_Coords;

  std::vector<ImplicitNeighbor> Neighbors;

  //------------------------------------------------------------------------------
  bool IsRectilinearGrid()
  {
    if ((this->X_Coords != nullptr) && (this->Y_Coords != nullptr) && (this->Z_Coords != nullptr))
    {
      return true;
    }
    return false;
  }

  //------------------------------------------------------------------------------
  void Clear()
  {
    if (this->Nodes != nullptr)
    {
      this->Nodes->Delete();
      this->Nodes = nullptr;
    }
    if (this->PointData != nullptr)
    {
      this->PointData->Delete();
      this->PointData = nullptr;
    }
    if (this->X_Coords != nullptr)
    {
      this->X_Coords->Delete();
      this->X_Coords = nullptr;
    }
    if (this->Y_Coords != nullptr)
    {
      this->Y_Coords->Delete();
      this->Y_Coords = nullptr;
    }
    if (this->Z_Coords != nullptr)
    {
      this->Z_Coords->Delete();
      this->Z_Coords = nullptr;
    }
    this->Neighbors.clear();
  }

  //------------------------------------------------------------------------------
  void Initialize(StructuredGrid* grid)
  {
    assert("pre: input grid is nullptr!" && (grid != nullptr));

    this->Initialize(grid->ID, grid->Extent, nullptr, nullptr);

    // Grow the extent in each dimension as needed
    for (int i = 0; i < 3; ++i)
    {
      if (grid->Grow[i] == 1)
      {
        this->Extent[i * 2 + 1] += 1;
      } // END if
    }   // END for all dimensions

    // the number of nodes in the grown extent
    vtkIdType nnodes = vtkStructuredData::GetNumberOfPoints(this->Extent, grid->DataDescription);

    // Allocate coordinates, if needed
    if (grid->Nodes != nullptr)
    {
      this->Nodes = vtkPoints::New();
      this->Nodes->SetDataType(grid->Nodes->GetDataType());
      this->Nodes->SetNumberOfPoints(nnodes);
    } // END if has points
    else
    {
      this->Nodes = nullptr;
    }

    // Allocate rectilinear grid coordinates, if needed
    if ((grid->X_Coords != nullptr) && (grid->Y_Coords != nullptr) && (grid->Z_Coords != nullptr))
    {
      int dims[3];
      vtkStructuredData::GetDimensionsFromExtent(this->Extent, dims, this->DataDescription);

      this->X_Coords = vtkDataArray::CreateDataArray(grid->X_Coords->GetDataType());
      this->X_Coords->SetNumberOfTuples(dims[0]);
      for (vtkIdType idx = 0; idx < grid->X_Coords->GetNumberOfTuples(); ++idx)
      {
        this->X_Coords->SetTuple(idx, idx, grid->X_Coords);
      }

      this->Y_Coords = vtkDataArray::CreateDataArray(grid->Y_Coords->GetDataType());
      this->Y_Coords->SetNumberOfTuples(dims[1]);
      for (vtkIdType idx = 0; idx < grid->Y_Coords->GetNumberOfTuples(); ++idx)
      {
        this->Y_Coords->SetTuple(idx, idx, grid->Y_Coords);
      }

      this->Z_Coords = vtkDataArray::CreateDataArray(grid->Z_Coords->GetDataType());
      this->Z_Coords->SetNumberOfTuples(dims[2]);
      for (vtkIdType idx = 0; idx < grid->Z_Coords->GetNumberOfTuples(); ++idx)
      {
        this->Z_Coords->SetTuple(idx, idx, grid->Z_Coords);
      }
    } // END if rectilinear grid
    else
    {
      grid->X_Coords = nullptr;
      grid->Y_Coords = nullptr;
      grid->Z_Coords = nullptr;
    }

    // Allocate fields, if needed
    if (grid->PointData != nullptr)
    {
      this->PointData = vtkPointData::New();
      this->PointData->CopyAllocate(grid->PointData, nnodes);

      // NOTE: CopyAllocate, allocates the buffers internally, but, does not
      // set the number of tuples of each array to nnodes.
      for (int array = 0; array < this->PointData->GetNumberOfArrays(); ++array)
      {
        vtkDataArray* a = this->PointData->GetArray(array);
        a->SetNumberOfTuples(nnodes);
      } // END for all arrays
    }
    else
    {
      this->PointData = nullptr;
    }

    // copy everything from the given grid
    int desc = grid->DataDescription;
    int ijk[3] = { 0, 0, 0 };

    for (I(ijk) = IMIN(grid->Extent); I(ijk) <= IMAX(grid->Extent); ++I(ijk))
    {
      for (J(ijk) = JMIN(grid->Extent); J(ijk) <= JMAX(grid->Extent); ++J(ijk))
      {
        for (K(ijk) = KMIN(grid->Extent); K(ijk) <= KMAX(grid->Extent); ++K(ijk))
        {
          // Compute the source index
          vtkIdType srcIdx = vtkStructuredData::ComputePointIdForExtent(grid->Extent, ijk, desc);

          // Compute the target index
          vtkIdType targetIdx = vtkStructuredData::ComputePointIdForExtent(this->Extent, ijk, desc);

          // Copy nodes
          if (this->Nodes != nullptr)
          {
            this->Nodes->SetPoint(targetIdx, grid->Nodes->GetPoint(srcIdx));
          }

          // Copy node-centered fields
          if (this->PointData != nullptr)
          {
            this->PointData->CopyData(grid->PointData, srcIdx, targetIdx);
          }

        } // END for all k
      }   // END for all j
    }     // END for all i
  }

  //------------------------------------------------------------------------------
  void Initialize(int id, int ext[6], vtkDataArray* x_coords, vtkDataArray* y_coords,
    vtkDataArray* z_coords, vtkPointData* fields)
  {
    assert("pre: nullptr x_coords!" && (x_coords != nullptr));
    assert("pre: nullptr y_coords!" && (y_coords != nullptr));
    assert("pre: nullptr z_coords!" && (z_coords != nullptr));

    this->ID = id;
    memcpy(this->Extent, ext, 6 * sizeof(int));
    this->DataDescription = vtkStructuredData::GetDataDescriptionFromExtent(ext);
    std::fill(this->Grow, this->Grow + 3, 0);
    std::fill(this->Implicit, this->Implicit + 3, 0);

    this->Nodes = nullptr;

    // Effectively, shallow copy the coordinate arrays and maintain ownership
    // of these arrays in the caller.
    this->X_Coords = vtkDataArray::CreateDataArray(x_coords->GetDataType());
    this->X_Coords->SetVoidArray(x_coords->GetVoidPointer(0), x_coords->GetNumberOfTuples(), 1);

    this->Y_Coords = vtkDataArray::CreateDataArray(y_coords->GetDataType());
    this->Y_Coords->SetVoidArray(y_coords->GetVoidPointer(0), y_coords->GetNumberOfTuples(), 1);

    this->Z_Coords = vtkDataArray::CreateDataArray(z_coords->GetDataType());
    this->Z_Coords->SetVoidArray(z_coords->GetVoidPointer(0), z_coords->GetNumberOfTuples(), 1);

    if (fields != nullptr)
    {
      this->PointData = vtkPointData::New();
      this->PointData->ShallowCopy(fields);
    }
    else
    {
      this->PointData = nullptr;
    }
  }

  //------------------------------------------------------------------------------
  void Initialize(int id, int ext[6], vtkPoints* nodes, vtkPointData* fields)
  {
    this->ID = id;
    memcpy(this->Extent, ext, 6 * sizeof(int));
    this->DataDescription = vtkStructuredData::GetDataDescriptionFromExtent(ext);
    std::fill(this->Grow, this->Grow + 3, 0);
    std::fill(this->Implicit, this->Implicit + 3, 0);

    this->X_Coords = nullptr;
    this->Y_Coords = nullptr;
    this->Z_Coords = nullptr;

    if (nodes != nullptr)
    {
      this->Nodes = vtkPoints::New();
      this->Nodes->ShallowCopy(nodes);
    }
    else
    {
      this->Nodes = nullptr;
    }

    if (fields != nullptr)
    {
      this->PointData = vtkPointData::New();
      this->PointData->ShallowCopy(fields);
    }
    else
    {
      this->PointData = nullptr;
    }
  }
};

//------------------------------------------------------------------------------
//  CommManager class Definition
//------------------------------------------------------------------------------

class CommunicationManager
{
public:
  CommunicationManager() {}
  ~CommunicationManager() { this->Clear(); }

  unsigned char* GetRcvBuffer(const int fromRank);
  unsigned int GetRcvBufferSize(const int fromRank);

  void EnqueueRcv(const int fromRank);
  void EnqueueSend(const int toRank, unsigned char* data, unsigned int nbytes);
  void Exchange(vtkMPIController* comm);
  int NumMsgs();
  void Clear();

private:
  // map send/rcv buffers based on rank.
  std::map<int, unsigned char*> Send;
  std::map<int, int> SendByteSize;
  std::map<int, unsigned char*> Rcv;
  std::map<int, int> RcvByteSize;
  std::vector<vtkMPICommunicator::Request> Requests;

  // exchanges buffer-sizes
  void AllocateRcvBuffers(vtkMPIController* comm);
};

//------------------------------------------------------------------------------
void CommunicationManager::Clear()
{
  this->Requests.clear();
  this->SendByteSize.clear();
  this->RcvByteSize.clear();

  std::map<int, unsigned char*>::iterator it;
  for (it = this->Send.begin(); it != this->Send.end(); ++it)
  {
    delete[] it->second;
  }
  this->Send.clear();

  for (it = this->Rcv.begin(); it != this->Rcv.end(); ++it)
  {
    delete[] it->second;
  }
  this->Rcv.clear();
}

//------------------------------------------------------------------------------
unsigned char* CommunicationManager::GetRcvBuffer(const int fromRank)
{
  assert(
    "pre: cannot find buffer for requested rank!" && (this->Rcv.find(fromRank) != this->Rcv.end()));
  return (this->Rcv[fromRank]);
}

//------------------------------------------------------------------------------
unsigned int CommunicationManager::GetRcvBufferSize(const int fromRank)
{
  assert("pre: cannot find bytesize size of requested rank!" &&
    (this->RcvByteSize.find(fromRank) != this->RcvByteSize.end()));
  return (this->RcvByteSize[fromRank]);
}

//------------------------------------------------------------------------------
int CommunicationManager::NumMsgs()
{
  return static_cast<int>(this->Send.size() + this->Rcv.size());
}

//------------------------------------------------------------------------------
void CommunicationManager::EnqueueRcv(const int fromRank)
{
  assert("pre: rcv from rank has already been enqueued!" &&
    (this->Rcv.find(fromRank) == this->Rcv.end()));

  this->Rcv[fromRank] = nullptr;
  this->RcvByteSize[fromRank] = 0;
}

//------------------------------------------------------------------------------
void CommunicationManager::EnqueueSend(const int toRank, unsigned char* data, unsigned int nbytes)
{
  assert("pre: send to rank has already been enqueued!" &&
    (this->Send.find(toRank) == this->Send.end()));

  this->Send[toRank] = data;
  this->SendByteSize[toRank] = nbytes;
}

//------------------------------------------------------------------------------
void CommunicationManager::AllocateRcvBuffers(vtkMPIController* comm)
{
  std::map<int, int>::iterator it;

  // STEP 0: Allocate vector to store request objects for non-blocking comm.
  int rqstIdx = 0;
  this->Requests.resize(this->NumMsgs());

  // STEP 1: Post receives
  for (it = this->RcvByteSize.begin(); it != this->RcvByteSize.end(); ++it)
  {
    int fromRank = it->first;
    int* dataPtr = &(it->second);
    comm->NoBlockReceive(dataPtr, 1, fromRank, 0, this->Requests[rqstIdx]);
    ++rqstIdx;
  }

  // STEP 2: Post Sends
  for (it = this->SendByteSize.begin(); it != this->SendByteSize.end(); ++it)
  {
    int toRank = it->first;
    int* dataPtr = &(it->second);
    comm->NoBlockSend(dataPtr, 1, toRank, 0, this->Requests[rqstIdx]);
    ++rqstIdx;
  }

  // STEP 3: WaitAll
  if (!this->Requests.empty())
  {
    comm->WaitAll(this->NumMsgs(), &this->Requests[0]);
  }
  this->Requests.clear();

  // STEP 4: Allocate rcv buffers
  std::map<int, unsigned char*>::iterator bufferIter = this->Rcv.begin();
  for (; bufferIter != this->Rcv.end(); ++bufferIter)
  {
    int fromRank = bufferIter->first;
    assert("pre: rcv buffer should be nullptr!" && (this->Rcv[fromRank] == nullptr));
    this->Rcv[fromRank] = new unsigned char[this->RcvByteSize[fromRank]];
  }
}

//------------------------------------------------------------------------------
void CommunicationManager::Exchange(vtkMPIController* comm)
{
  std::map<int, unsigned char*>::iterator it;

  // STEP 0: exchange & allocate buffer sizes
  this->AllocateRcvBuffers(comm);

  // STEP 1: Allocate vector to store request objects for non-blocking comm.
  int rqstIdx = 0;
  this->Requests.resize(this->NumMsgs());

  // STEP 2: Post Rcvs
  for (it = this->Rcv.begin(); it != this->Rcv.end(); ++it)
  {
    int fromRank = it->first;
    unsigned char* buffer = it->second;
    assert("pre: rcv buffer size not found!" &&
      this->RcvByteSize.find(fromRank) != this->RcvByteSize.end());
    unsigned int bytesize = this->RcvByteSize[fromRank];

    comm->NoBlockReceive(buffer, bytesize, fromRank, 0, this->Requests[rqstIdx]);
    ++rqstIdx;
  }

  // STEP 3: Post Sends
  for (it = this->Send.begin(); it != this->Send.end(); ++it)
  {
    int toRank = it->first;
    unsigned char* buffer = it->second;
    assert("pre: rcv buffer size not found!" &&
      this->SendByteSize.find(toRank) != this->SendByteSize.end());
    unsigned int bytesize = this->SendByteSize[toRank];

    comm->NoBlockSend(buffer, bytesize, toRank, 0, this->Requests[rqstIdx]);
    ++rqstIdx;
  }

  // STEP 4: WaitAll
  if (!this->Requests.empty())
  {
    comm->WaitAll(this->NumMsgs(), &this->Requests[0]);
  }
  this->Requests.clear();
}

} // END namespace detail
} // END namespace vtk
//==============================================================================
// END INTERNAL DATASTRUCTURE DEFINITIONS
//==============================================================================

vtkStandardNewMacro(vtkStructuredImplicitConnectivity);

//------------------------------------------------------------------------------
vtkStructuredImplicitConnectivity::vtkStructuredImplicitConnectivity()
{
  this->DomainInfo = nullptr;
  this->InputGrid = nullptr;
  this->OutputGrid = nullptr;
  this->CommManager = nullptr;
  this->Controller =
    vtkMPIController::SafeDownCast(vtkMultiProcessController::GetGlobalController());
}

//------------------------------------------------------------------------------
vtkStructuredImplicitConnectivity::~vtkStructuredImplicitConnectivity()
{
  delete this->DomainInfo;
  this->DomainInfo = nullptr;

  if (this->InputGrid != nullptr)
  {
    this->InputGrid->Clear();
    delete this->InputGrid;
    this->InputGrid = nullptr;
  }

  if (this->OutputGrid != nullptr)
  {
    this->OutputGrid->Clear();
    delete this->OutputGrid;
    this->OutputGrid = nullptr;
  }

  if (this->CommManager != nullptr)
  {
    this->CommManager->Clear();
    delete this->CommManager;
    this->CommManager = nullptr;
  }

  this->Controller = nullptr;
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::PrintSelf(ostream& os, vtkIndent indent)
{
  this->Superclass::PrintSelf(os, indent);
  os << "Controller: " << this->Controller << std::endl;
  if (this->Controller != nullptr)
  {
    os << "Number of Ranks: " << this->Controller->GetNumberOfProcesses();
    os << std::endl;
  } // END if Controller != nullptr

  os << "Input Grid: " << this->InputGrid << std::endl;
  if (this->InputGrid != nullptr)
  {
    os << "Extent: [" << this->InputGrid->Extent[0];
    os << ", " << this->InputGrid->Extent[1];
    os << ", " << this->InputGrid->Extent[2];
    os << ", " << this->InputGrid->Extent[3];
    os << ", " << this->InputGrid->Extent[4];
    os << ", " << this->InputGrid->Extent[5];
    os << "] " << std::endl;

    os << "Grow: [" << this->InputGrid->Grow[0];
    os << ", " << this->InputGrid->Grow[1];
    os << ", " << this->InputGrid->Grow[2];
    os << "] " << std::endl;

    os << "Number of Neighbors: " << this->InputGrid->Neighbors.size();
    os << std::endl;
    size_t N = this->InputGrid->Neighbors.size();
    for (size_t nei = 0; nei < N; ++nei)
    {
      os << "\t" << this->InputGrid->Neighbors[nei].ToString();
      os << std::endl;
    } // END for all neighbors
  }   // END if InputGrid != nullptr
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::SetWholeExtent(int wholeExt[6])
{
  delete this->DomainInfo;

  this->DomainInfo = new vtk::detail::DomainMetaData();
  this->DomainInfo->Initialize(wholeExt);

  assert(
    "post: Domain description does not match across ranks!" && this->GlobalDataDescriptionMatch());
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::RegisterGrid(
  const int gridID, int extent[6], vtkPoints* gridNodes, vtkPointData* pointData)
{
  // Sanity Checks!
  assert("pre: nullptr Domain, whole extent is not set!" && (this->DomainInfo != nullptr));
  assert("pre: input not nullptr in this process!" && (this->InputGrid == nullptr));
  assert("pre: input grid ID should be >= 0" && (gridID >= 0));

  delete this->InputGrid;
  this->InputGrid = nullptr;

  // Only add if the grid falls within the output extent. Processes that do
  // not contain the VOI will fail this test.
  if (this->DomainInfo->HasGrid(extent))
  {
    this->InputGrid = new vtk::detail::StructuredGrid();
    this->InputGrid->Initialize(gridID, extent, gridNodes, pointData);
  }
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::RegisterRectilinearGrid(const int gridID, int extent[6],
  vtkDataArray* xcoords, vtkDataArray* ycoords, vtkDataArray* zcoords, vtkPointData* pointData)
{
  // Sanity Checks!
  assert("pre: nullptr Domain, whole extent is not set!" && (this->DomainInfo != nullptr));
  assert("pre: input not nullptr in this process!" && (this->InputGrid == nullptr));
  assert("pre: input grid ID should be >= 0" && (gridID >= 0));

  delete this->InputGrid;
  this->InputGrid = nullptr;

  // Only add if the grid falls within the output extent. Processes that do
  // not contain the VOI will fail this test.
  if (this->DomainInfo->HasGrid(extent))
  {
    this->InputGrid = new vtk::detail::StructuredGrid();
    this->InputGrid->Initialize(gridID, extent, xcoords, ycoords, zcoords, pointData);
  }
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::ExchangeExtents()
{
  // Sanity checks!
  assert("pre: null controller!" && (this->Controller != nullptr));
  assert("pre: null domain!" && (this->DomainInfo != nullptr));

  // STEP 0: Construct the extent buffer that will be sent from each process.
  // Each process sends 7 ints: [gridId imin imax jmin jmax kmin kmax]
  int extbuffer[7];
  if (this->InputGrid == nullptr)
  {
    // pad the buffer with -1, indicating that this process has no grid
    std::fill(extbuffer, extbuffer + 7, -1);
  }
  else
  {
    extbuffer[0] = this->InputGrid->ID;
    memcpy(&extbuffer[1], this->InputGrid->Extent, 6 * sizeof(int));
  }

  // STEP 1: Allocate receive buffer, we receive 7 ints for each rank
  int nranks = this->Controller->GetNumberOfProcesses();
  this->DomainInfo->ExtentListInfo.resize(7 * nranks, 0);

  // STEP 2: AllGather
  int* rcvbuffer = &(this->DomainInfo->ExtentListInfo)[0];
  this->Controller->AllGather(extbuffer, rcvbuffer, 7);
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::ComputeNeighbors()
{
  if (!this->InputGrid)
  {
    return;
  }

  int type;
  vtk::detail::Interval A;                // used to store the local interval at each dim
  vtk::detail::Interval B;                // used to store the remote interval at each dim
  vtk::detail::Interval Overlap;          // used to store the computed overlap
  vtk::detail::ImplicitNeighbor Neighbor; // used to store neighbor information

  int nranks = this->Controller->GetNumberOfProcesses();
  for (int rank = 0; rank < nranks; ++rank)
  {
    int rmtID = this->DomainInfo->ExtentListInfo[rank * 7];
    if ((rmtID == this->InputGrid->ID) || (rmtID == -1))
    {
      // skip self or empty remote grid
      continue;
    }

    int* rmtExtent = &(this->DomainInfo->ExtentListInfo)[rank * 7 + 1];

    // Initialize neighbor data-structure
    Neighbor.Rank = rank;
    memcpy(Neighbor.Extent, rmtExtent, 6 * sizeof(int));
    memcpy(Neighbor.Overlap, Neighbor.Extent, 6 * sizeof(int));
    std::fill(
      Neighbor.Orientation, Neighbor.Orientation + 3, vtk::detail::IntervalsConnect::UNDEFINED);

    bool disregard = false;
    int nimplicit = 0;

    for (int dim = 0; dim < this->DomainInfo->NDim; ++dim)
    {
      int d = this->DomainInfo->DimIndex[dim];
      assert("pre: invalid dimension!" && (d >= 0) && (d <= 2));

      A.Set(this->InputGrid->Extent[d * 2], this->InputGrid->Extent[d * 2 + 1]);
      B.Set(rmtExtent[d * 2], rmtExtent[d * 2 + 1]);

      if (A.ImplicitNeighbor(B, type))
      {
        this->InputGrid->Implicit[d] = 1;
        Neighbor.Orientation[d] = type;

        // Compute overlap based on the fact that we are communicating
        // data to the left <=> grow to the right.
        if (type == vtk::detail::IntervalsConnect::IMPLICIT_HI)
        {
          ++nimplicit;
          Neighbor.Overlap[d * 2] = Neighbor.Overlap[d * 2 + 1] = Neighbor.Extent[d * 2];
          this->InputGrid->Grow[d] = 1; /* increment by 1 in this dimension */
        }                               // END if IMPLICIT_HI
        else if (type == vtk::detail::IntervalsConnect::IMPLICIT_LO)
        {
          ++nimplicit;
          Neighbor.Overlap[d * 2] = Neighbor.Overlap[d * 2 + 1] = this->InputGrid->Extent[d * 2];
        } // END else if IMPLICIT_LO
        else
        {
          vtkGenericWarningMacro(<< "Invalid implicit connectivity type! "
                                 << "Code should not reach here!\n");
        } // END else
      }   // END if implicit
      else if (A.Intersects(B, Overlap, type))
      {
        Neighbor.Orientation[d] = type;
        Neighbor.Overlap[d * 2] = Overlap.Low();
        Neighbor.Overlap[d * 2 + 1] = Overlap.High();
      } // END if intersect
      else
      {
        disregard = true;
        Neighbor.Orientation[d] = type;
      } // END else
    }   // END for all dimensions

    // Determine whether to include the neighbor to the list of neighbors in
    // this rank.

    if (!(nimplicit > 1 || disregard))
    {
      this->InputGrid->Neighbors.push_back(Neighbor);
    }

  } // END for all ranks
}

//------------------------------------------------------------------------------
bool vtkStructuredImplicitConnectivity::GlobalDataDescriptionMatch()
{
  int sum = -1;
  this->Controller->AllReduce(&this->DomainInfo->DataDescription, &sum, 1, vtkCommunicator::SUM_OP);
  if ((sum / this->Controller->GetNumberOfProcesses()) == this->DomainInfo->DataDescription)
  {
    return true;
  }
  return false;
}

//------------------------------------------------------------------------------
bool vtkStructuredImplicitConnectivity::HasImplicitConnectivity()
{
  if (this->DomainInfo == nullptr)
  {
    vtkGenericWarningMacro(<< "nullptr domain, WholeExtent not set!");
    return false;
  }

  if ((this->DomainInfo->GlobalImplicit[0] > 0) || (this->DomainInfo->GlobalImplicit[1] > 0) ||
    (this->DomainInfo->GlobalImplicit[2] > 0))
  {
    return true;
  }
  return false;
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::GetGlobalImplicitConnectivityState()
{
  // Sanity checks!
  assert("pre: null controller!" && (this->Controller != nullptr));

  int sndbuffer[3];
  if (this->InputGrid == nullptr)
  {
    std::fill(sndbuffer, sndbuffer + 3, 0);
  }
  else
  {
    memcpy(sndbuffer, this->InputGrid->Implicit, 3 * sizeof(int));
  }

  this->Controller->AllReduce(
    sndbuffer, this->DomainInfo->GlobalImplicit, 3, vtkCommunicator::SUM_OP);
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::EstablishConnectivity()
{
  // Sanity checks!
  assert("pre: null controller!" && (this->Controller != nullptr));
  assert("pre: nullptr domain, WholeExtent not set!" && (this->DomainInfo != nullptr));

  // STEP 0: Exchange extents
  this->ExchangeExtents();

  // STEP 1: Compute Neighbors
  this->ComputeNeighbors();

  // STEP 2: Get Global Implicit connectivity state
  this->GetGlobalImplicitConnectivityState();

  // STEP 3: Barrier synchronization
  this->Controller->Barrier();
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::GetOutputStructuredGrid(
  const int gridID, vtkStructuredGrid* grid)
{
  assert("pre: nullptr output grid!" && (grid != nullptr));
  assert("pre: output grid is nullptr!" && (this->OutputGrid != nullptr));
  assert("pre: mismatch gridID" && (this->OutputGrid->ID == gridID));
  assert("pre: output grid has no points!" && (this->OutputGrid->Nodes != nullptr));

  // silence warnings, the intent for the gridID here is for extending the
  // implementation in the future to allow multiple grids per process.
  static_cast<void>(gridID);

  grid->Initialize();
  grid->SetExtent(this->OutputGrid->Extent);
  grid->SetPoints(this->OutputGrid->Nodes);
  grid->GetPointData()->ShallowCopy(this->OutputGrid->PointData);
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::GetOutputImageData(const int gridID, vtkImageData* grid)
{
  assert("pre: nullptr output grid!" && (grid != nullptr));
  assert("pre: output grid is nullptr!" && (this->OutputGrid != nullptr));
  assert("pre: mismatch gridID" && (this->OutputGrid->ID == gridID));

  // silence warnings, the intent for the gridID here is for extending the
  // implementation in the future to allow multiple grids per process.
  static_cast<void>(gridID);

  grid->SetExtent(this->OutputGrid->Extent);
  grid->GetPointData()->ShallowCopy(this->OutputGrid->PointData);
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::GetOutputRectilinearGrid(
  const int gridID, vtkRectilinearGrid* grid)
{
  assert("pre: nullptr output grid!" && (grid != nullptr));
  assert("pre: output grid is nullptr!" && (this->OutputGrid != nullptr));
  assert("pre: mismatch gridID" && (this->OutputGrid->ID == gridID));

  // silence warnings, the intent for the gridID here is for extending the
  // implementation in the future to allow multiple grids per process.
  static_cast<void>(gridID);

  grid->SetExtent(this->OutputGrid->Extent);
  grid->GetPointData()->ShallowCopy(this->OutputGrid->PointData);
  grid->SetXCoordinates(this->OutputGrid->X_Coords);
  grid->SetYCoordinates(this->OutputGrid->Y_Coords);
  grid->SetZCoordinates(this->OutputGrid->Z_Coords);
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::ConstructOutput()
{
  if (this->OutputGrid != nullptr)
  {
    this->OutputGrid->Clear();
    delete this->OutputGrid;
    this->OutputGrid = nullptr;
  }

  this->OutputGrid = new vtk::detail::StructuredGrid();
  this->OutputGrid->Initialize(this->InputGrid);
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::UpdateNeighborList(const int dim)
{
  assert("pre: dimension index out-of-bounds!" && (dim >= 0) && (dim <= 2));
  assert("pre: input grid is nullptr!" && this->InputGrid != nullptr);
  assert("pre: domain info is nullptr!" && this->DomainInfo != nullptr);

  vtk::detail::ImplicitNeighbor* neiPtr = nullptr;
  size_t nNeis = this->InputGrid->Neighbors.size();
  for (size_t nei = 0; nei < nNeis; ++nei)
  {
    neiPtr = &(this->InputGrid->Neighbors)[nei];
    int orient = neiPtr->Orientation[dim];

    if (orient == vtk::detail::IntervalsConnect::IMPLICIT_HI ||
      orient == vtk::detail::IntervalsConnect::IMPLICIT_LO ||
      orient == vtk::detail::IntervalsConnect::UNDEFINED)
    {
      continue;
    } // END if implicit connectivity

    // Update neighbor extent
    if (neiPtr->Extent[dim * 2 + 1] < this->DomainInfo->WholeExtent[dim * 2 + 1])
    {
      neiPtr->Extent[dim * 2 + 1]++;
    } // END if update neighbor extent

    // Update overlap extent
    if (neiPtr->Overlap[dim * 2 + 1] < this->DomainInfo->WholeExtent[dim * 2 + 1] &&
      neiPtr->Overlap[dim * 2 + 1] + 1 <= neiPtr->Extent[dim * 2 + 1])
    {
      neiPtr->Overlap[dim * 2 + 1]++;
    } // END if update overlap

    assert("post: overlap extent out-of-bounds of output grid extent!" &&
      vtkStructuredExtent::Smaller(neiPtr->Overlap, this->OutputGrid->Extent));
  } // END for all neighbors
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::PackData(int ext[6], vtkMultiProcessStream& bytestream)
{
  // Sanity checks
  assert("pre: input grid is nullptr!" && (this->InputGrid != nullptr));
  assert("pre: output grid is nullptr!" && (this->OutputGrid != nullptr));
  assert("pre: extent is out-of-bounds the output grid!" &&
    vtkStructuredExtent::Smaller(ext, this->OutputGrid->Extent));

  bytestream.Push(ext, 6);

  if (this->OutputGrid->Nodes != nullptr)
  {
    bytestream << VTK_STRUCTURED_GRID;
    vtkIdType nnodes = vtkStructuredData::GetNumberOfPoints(ext);
    bytestream << nnodes;

    int ijk[3] = { 0, 0, 0 };
    for (I(ijk) = IMIN(ext); I(ijk) <= IMAX(ext); ++I(ijk))
    {
      for (J(ijk) = JMIN(ext); J(ijk) <= JMAX(ext); ++J(ijk))
      {
        for (K(ijk) = KMIN(ext); K(ijk) <= KMAX(ext); ++K(ijk))
        {
          vtkIdType idx = vtkStructuredData::ComputePointIdForExtent(
            this->OutputGrid->Extent, ijk, this->OutputGrid->DataDescription);
          bytestream.Push(this->OutputGrid->Nodes->GetPoint(idx), 3);
        } // END for all k
      }   // END for all j
    }     // END for all i
  }       // END if structured grid
  else if (this->OutputGrid->IsRectilinearGrid())
  {
    bytestream << VTK_RECTILINEAR_GRID;
    vtkDataArray* coords[3];
    coords[0] = this->OutputGrid->X_Coords;
    coords[1] = this->OutputGrid->Y_Coords;
    coords[2] = this->OutputGrid->Z_Coords;
    for (int dim = 0; dim < 3; ++dim)
    {
      assert("pre: nullptr coordinates" && coords[dim] != nullptr);
      int flag = -1;
      if (ext[dim * 2] == ext[dim * 2 + 1])
      {
        flag = 1;
        bytestream << flag;
        bytestream << coords[dim]->GetTuple1(0);
      }
      else
      {
        bytestream << flag;
      }
    } // END for all dimensions
  }   // END if rectilinear grid
  else
  {
    bytestream << VTK_UNIFORM_GRID;
  }

  // serialize the node-centered fields
  if (this->OutputGrid->PointData != nullptr)
  {
    vtkFieldDataSerializer::SerializeSubExtent(
      ext, this->OutputGrid->Extent, this->OutputGrid->PointData, bytestream);
  }
  else
  {
    bytestream << 0;
  }
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::UnPackData(unsigned char* buffer, unsigned int size)
{
  assert("pre: output grid is nullptr!" && (this->OutputGrid != nullptr));

  if (size == 0)
  {
    return;
  }

  assert("pre: nullptr buffer encountered!" && (buffer != nullptr));

  vtkMultiProcessStream bytestream;
  bytestream.SetRawData(buffer, size);

  int* ext = nullptr;
  unsigned int sz = 0;
  bytestream.Pop(ext, sz);
  assert("post: ext size should be 6" && (sz == 6));
  assert("post: ext is out-of-bounds the output grid!" &&
    vtkStructuredExtent::Smaller(ext, this->OutputGrid->Extent));

  int datatype = -1;
  bytestream >> datatype;

  if (datatype == VTK_STRUCTURED_GRID)
  {
    int nnodes = 0;
    bytestream >> nnodes;
    assert("pre: nnodes must be greater than 0!" && (nnodes > 0));
    assert("post: output grid must have nodes!" && (this->OutputGrid->Nodes != nullptr));

    int ijk[3] = { 0, 0, 0 };
    double* pnt = new double[3];
    unsigned int pntsz = 3;

    for (I(ijk) = IMIN(ext); I(ijk) <= IMAX(ext); ++I(ijk))
    {
      for (J(ijk) = JMIN(ext); J(ijk) <= JMAX(ext); ++J(ijk))
      {
        for (K(ijk) = KMIN(ext); K(ijk) <= KMAX(ext); ++K(ijk))
        {
          vtkIdType idx = vtkStructuredData::ComputePointIdForExtent(
            this->OutputGrid->Extent, ijk, this->OutputGrid->DataDescription);
          assert("post: idx is out-of-bounds!" && (idx >= 0) &&
            (idx < this->OutputGrid->Nodes->GetNumberOfPoints()));

          bytestream.Pop(pnt, pntsz);
          assert("post: pntsz!=3" && (pntsz == 3));

          this->OutputGrid->Nodes->SetPoint(idx, pnt);
        } // END for all k
      }   // END for all j
    }     // END for all i

    delete[] pnt;
  } // END if structured
  else if (datatype == VTK_RECTILINEAR_GRID)
  {
    vtkDataArray* coords[3];
    coords[0] = this->OutputGrid->X_Coords;
    coords[1] = this->OutputGrid->Y_Coords;
    coords[2] = this->OutputGrid->Z_Coords;
    for (int dim = 0; dim < 3; ++dim)
    {
      assert("pre: nullptr coordinates" && coords[dim] != nullptr);
      int flag = 0;
      bytestream >> flag;
      if (flag == 1)
      {
        double coordinate;
        vtkIdType lastIdx = coords[dim]->GetNumberOfTuples() - 1;
        bytestream >> coordinate;
        coords[dim]->SetTuple1(lastIdx, coordinate);
      }
    } // END for all dimensions
  }   // END if rectilinear

  // de-serialize the node-centered fields
  if (this->OutputGrid->PointData != nullptr)
  {
    vtkFieldDataSerializer::DeSerializeToSubExtent(
      ext, this->OutputGrid->Extent, this->OutputGrid->PointData, bytestream);
  }

  delete[] ext;
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::AllocateBuffers(const int dim)
{
  assert("pre: dimension index out-of-bounds!" && (dim >= 0) && (dim <= 2));

  // Allocate CommBuffer data-structure
  if (this->CommManager == nullptr)
  {
    this->CommManager = new vtk::detail::CommunicationManager();
  }

  // Clear previously calculated buffers, since we call this iteratively as
  // we carry out the communication along each dimension independently.
  this->CommManager->Clear();

  size_t nNeis = this->InputGrid->Neighbors.size();
  for (size_t nei = 0; nei < nNeis; ++nei)
  {
    vtk::detail::ImplicitNeighbor* neiPtr = &(this->InputGrid->Neighbors)[nei];
    int orient = neiPtr->Orientation[dim];

    if (orient == vtk::detail::IntervalsConnect::IMPLICIT_HI)
    {
      // enqueue rcv from the rank of this neighbor
      this->CommManager->EnqueueRcv(neiPtr->Rank);
    } // END if
    else if (orient == vtk::detail::IntervalsConnect::IMPLICIT_LO)
    {
      // enqueue send to the rank of this neighbor
      vtkMultiProcessStream bytestream;
      this->PackData(neiPtr->Overlap, bytestream);

      unsigned char* buffer = nullptr;
      unsigned int bytesize = 0;
      bytestream.GetRawData(buffer, bytesize);

      this->CommManager->EnqueueSend(neiPtr->Rank, buffer, bytesize);
    } // END else if
  }   // END for all neighbors
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::GrowGrid(const int dim)
{
  assert("pre: dimension index out-of-bounds!" && (dim >= 0) && (dim <= 2));
  assert("pre: input grid is nullptr!" && this->InputGrid != nullptr);

  // STEP 0: Allocate buffers & associated data-structures
  this->AllocateBuffers(dim);
  assert("pre: CommManager is nullptr!" && (this->CommManager != nullptr));

  // STEP 1: Exchange data
  this->CommManager->Exchange(this->Controller);

  // STEP 4: Unpack data to output grid
  size_t nNeis = this->InputGrid->Neighbors.size();
  for (size_t nei = 0; nei < nNeis; ++nei)
  {
    vtk::detail::ImplicitNeighbor* neiPtr = &(this->InputGrid->Neighbors)[nei];
    int orient = neiPtr->Orientation[dim];
    int neiRank = neiPtr->Rank;

    if (orient == vtk::detail::IntervalsConnect::IMPLICIT_HI)
    {
      unsigned char* buffer = this->CommManager->GetRcvBuffer(neiRank);
      unsigned int size = this->CommManager->GetRcvBufferSize(neiRank);
      this->UnPackData(buffer, size);
    } // END if rcv'ed data

  } // END for all neighbors
}

//------------------------------------------------------------------------------
void vtkStructuredImplicitConnectivity::ExchangeData()
{
  // Sanity checks!
  assert("pre: null controller!" && (this->Controller != nullptr));

  if (this->InputGrid != nullptr)
  {
    // STEP 0: construct output grid data-structure
    this->ConstructOutput();

    // STEP 1: Process each dimension
    for (int d = 0; d < this->DomainInfo->NDim; ++d)
    {
      int dim = this->DomainInfo->DimIndex[d];
      this->GrowGrid(dim);

      // STEP 2: Update neighbor list, w/ the grown grid information
      this->UpdateNeighborList(dim);
    } // END for all dimensions
  }   // END if
  else
  {
    this->OutputGrid = nullptr;
  } // END else

  // Barrier synchronization
  this->Controller->Barrier();
}
