#ifndef HPC_MPI_MATRIX_HPP
#define HPC_MPI_MATRIX_HPP 1

#include <cassert>
#include <memory>
#include <type_traits>
#include <vector>
#include <mpi.h>
#include <hpc/aux/slices.hpp>
#include <hpc/matvec/gematrix.hpp>
#include <hpc/mpi/fundamental.hpp>

namespace hpc { namespace mpi {

/* construct MPI data type for a row of Matrix A
   where the extent is adapted such that consecutive
   rows can be combined even if they overlap */
template<typename T, template<typename> class Matrix,
   Require<Ge<Matrix<T>>> = true>
MPI_Datatype get_row_type(const Matrix<T>& A) {
   MPI_Datatype rowtype;
   MPI_Type_vector(
      /* count = */ A.numCols(),
      /* blocklength = */ 1,
      /* stride = */ A.incCol(),
      /* element type = */ get_type(A(0, 0)),
      /* newly created type = */ &rowtype);

   /* in case of row-major we are finished */
   if (A.incRow() == A.numCols()) {
      MPI_Type_commit(&rowtype);
      return rowtype;
   }

   /* the extent of the MPI data type does not match
      the offset of subsequent rows -- this is a problem
      whenever we want to handle more than one row;
      to fix this we need to use the resize function
      which allows us to adapt the extent to A.incRow() */
   MPI_Datatype resized_rowtype;
   MPI_Type_create_resized(rowtype, 0, /* lb remains unchanged */
      A.incRow() * sizeof(T), &resized_rowtype);
   MPI_Type_commit(&resized_rowtype);
   MPI_Type_free(&rowtype);
   return resized_rowtype;
}

/* create MPI data type for matrix A */
template<typename T, template<typename> class Matrix,
   Require<Ge<Matrix<T>>> = true>
MPI_Datatype get_type(const Matrix<T>& A) {
   MPI_Datatype datatype;
   if (A.incCol() == 1) {
      MPI_Type_vector(
	 /* count = */ A.numRows(),
	 /* blocklength = */ A.numCols(),
	 /* stride = */ A.incRow(),
	 /* element type = */ get_type(A(0, 0)),
	 /* newly created type = */ &datatype);
   } else {
      /* vector of row vectors */
      MPI_Datatype rowtype = get_row_type(A);
      MPI_Type_contiguous(A.numRows(), rowtype, &datatype);
      MPI_Type_free(&rowtype);
   }
   MPI_Type_commit(&datatype);
   return datatype;
}

} } // namespaces mpi, hpc

#endif // HPC_MPI_MATRIX_H