!>
!> @file p2p_mat.tpl
!>
!> @brief
!>
!> @copyright
!> Copyright (©) 2021 EPFL (Ecole Polytechnique Fédérale de Lausanne)
!> SPC (Swiss Plasma Center)
!>
!> SPClibs is free software: you can redistribute it and/or modify it under
!> the terms of the GNU Lesser General Public License as published by the Free
!> Software Foundation, either version 3 of the License, or (at your option)
!> any later version.
!>
!> SPClibs is distributed in the hope that it will be useful, but WITHOUT ANY
!> WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
!> FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
!>
!> You should have received a copy of the GNU Lesser General Public License
!> along with this program. If not, see <https://www.gnu.org/licenses/>.
!>
!> @author
!> (in alphabetical order)
!> @author Trach-Minh Tran <trach-minh.tran@epfl.ch>
!>
    INTEGER, INTENT(in)          :: dest
    CHARACTER(len=*), INTENT(in) :: extyp ! ('send', 'recv', 'sendrecv')
    CHARACTER(len=*), INTENT(in) :: op    ! ('put', 'updt')
    INTEGER, INTENT(in)          :: comm
!
    INTEGER :: ierr
    INTEGER :: nrank, nnz, nnz_rem
    INTEGER :: i, s, idx, bufsize, position
    CHARACTER(len=1), ALLOCATABLE :: sbuf(:), rbuf(:)
    INTEGER, ALLOCATABLE :: irow(:), cols(:)
!--------------------------------------------------------------------------
!                    1.0  Prologue
!
    nrank = mat%rank
    nnz = get_count(mat)
    CALL mpi_sendrecv(nnz, 1, MPI_INTEGER, dest, 0, &
         &            nnz_rem, 1, MPI_INTEGER, dest, 0, &
         &            comm, MPI_STATUS_IGNORE, ierr)
!--------------------------------------------------------------------------
!                    2.0  Send or sendrecv
!
    IF(extyp.EQ.'send' .OR. extyp.EQ.'sendrecv') THEN
!
!    Allocate packed send buffer
       bufsize = 0
       CALL mpi_pack_size(nrank+1, MPI_INTEGER, comm, s, ierr); bufsize=bufsize+s
       CALL mpi_pack_size(nnz, MPI_INTEGER, comm, s, ierr); bufsize=bufsize+s
       CALL mpi_pack_size(nnz, mpi_type, comm, s, ierr); bufsize=bufsize+s
       ALLOCATE(sbuf(bufsize))
!
!    Obtain matrix CSR arrays and pack
       CALL to_mat(mat, nlkeep=.TRUE.)
       position = 0
       CALL mpi_pack(mat%irow, nrank+1, MPI_INTEGER, sbuf, bufsize, position, comm, ierr)
       CALL mpi_pack(mat%cols, nnz, MPI_INTEGER, sbuf, bufsize, position, comm, ierr)
       CALL mpi_pack(mat%val, nnz, mpi_type, sbuf, bufsize, position, comm, ierr)
       DEALLOCATE(mat%irow)
       DEALLOCATE(mat%cols)
       DEALLOCATE(mat%val)
!
!   Communicate packed buffer
       IF(extyp.EQ.'send') THEN
          CALL mpi_send(sbuf, position, MPI_PACKED, dest, 0, comm, ierr)
          DEALLOCATE(sbuf)
       END IF
    END IF
!--------------------------------------------------------------------------
!                    3.0  Sendrecv or recv
!
    IF(extyp.EQ.'recv' .OR. extyp.EQ.'sendrecv') THEN
!
!    Allocate unpacked received buffer
       bufsize = 0
       CALL mpi_pack_size(nrank+1, MPI_INTEGER, comm, s, ierr); bufsize=bufsize+s
       CALL mpi_pack_size(nnz_rem, MPI_INTEGER, comm, s, ierr); bufsize=bufsize+s
       CALL mpi_pack_size(nnz_rem, mpi_type, comm, s, ierr); bufsize=bufsize+s
       ALLOCATE(rbuf(bufsize))
!
!    Communicate packed buffer
       IF(extyp.EQ.'recv') THEN
          CALL mpi_recv(rbuf, bufsize, MPI_PACKED, dest, 0, comm, MPI_STATUS_IGNORE, ierr)
       ELSE IF(extyp.EQ.'sendrecv') THEN
          CALL mpi_sendrecv(sbuf, position, MPI_PACKED, dest, 0, &
               &            rbuf, bufsize, MPI_PACKED, dest, 0, &
               &            comm, MPI_STATUS_IGNORE, ierr)
          DEALLOCATE(sbuf)
       END IF
!
!    Unpacked rbuf
       ALLOCATE(irow(nrank+1))
       ALLOCATE(cols(nnz_rem))
       ALLOCATE(val(nnz_rem))
       position = 0
       CALL mpi_unpack(rbuf, bufsize, position, irow, nrank+1, MPI_INTEGER, comm, ierr)
       CALL mpi_unpack(rbuf, bufsize, position, cols, nnz_rem, MPI_INTEGER, comm, ierr)
       CALL mpi_unpack(rbuf, bufsize, position, val, nnz_rem, mpi_type, comm, ierr)
       DEALLOCATE(rbuf)
!
!    Update/replace sparse matrix
       DO i=1,nrank
          DO idx=irow(i),irow(i+1)-1
             IF(op.EQ.'updt') THEN
                CALL updtmat(mat, i, cols(idx), val(idx))
             ELSE IF(op.EQ.'put') THEN
                CALL putele(mat, i, cols(idx), val(idx))
             END IF
          END DO
       END DO
       DEALLOCATE(irow)
       DEALLOCATE(cols)
       DEALLOCATE(val)
!      
    END IF
!--------------------------------------------------------------------------