/* ///////////////////////////////////////////////////////////////////// */
/*! 
  \file  
  \brief Data communication in a ring.

  For each processor, define a unique string defining the process
  color and perform n cyclic permutations by transferring the color
  name to the process to the right.
  Three versions are provided:

  i)   using MPI_Send / Recv()   (select VERSION == 0);
  ii)  using MPI_Sendrecv()      (select VERSION == 1);
  iii) using MPI_Isend / Irecv() (select VERSION == 2). 
  
  \author A. Mignone (mignone@to.infn.it)
  \date   March 10, 2020
*/
/* ///////////////////////////////////////////////////////////////////// */


#include <mpi.h>
#include <stdio.h>

#define STR_LENGTH 32
#define VERSION 1

int main(int argc, char ** argv)
{
  int rank, size;
  int dstL, dstR;
  char recv_buf[STR_LENGTH];
  char send_buf[STR_LENGTH];
  MPI_Request req;
  
/* -- 1. Initialize the MPI execution environment -- */

  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

/* -- 2. Define color -- */

  if (rank == 0) sprintf (send_buf, "red");
  if (rank == 1) sprintf (send_buf, "blue");
  if (rank == 2) sprintf (send_buf, "green");
  if (rank == 3) sprintf (send_buf, "black");
  if (rank == 4) sprintf (send_buf, "orange");
  if (rank == 5) sprintf (send_buf, "yellow");

  if (size > 6){
    if (rank == 0) printf ("! Cannot execute with more than six processes\n");
    MPI_Finalize();
    return 0;
  }

/* -- 3. Determine neighbour processors -- */

  dstL  = rank - 1;
  dstR  = rank + 1;
  if (dstL < 0)     dstL = size-1;
  if (dstR >= size) dstR = 0;

  int n;
  for (n = 0; n < size; n++){ 
    #if VERSION == 1
    MPI_Send(send_buf, STR_LENGTH, MPI_CHAR, dstR, 0, MPI_COMM_WORLD);
    MPI_Recv(recv_buf, STR_LENGTH, MPI_CHAR, dstL, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    #elif VERSION == 2
    MPI_Sendrecv(send_buf, STR_LENGTH, MPI_CHAR, dstR, 0,
                 recv_buf, STR_LENGTH, MPI_CHAR, dstL, 0, MPI_COMM_WORLD,
                 MPI_STATUS_IGNORE);
    #elif VERSION == 3
    MPI_Isend(send_buf, STR_LENGTH, MPI_CHAR, dstR, 0, MPI_COMM_WORLD, &req);
    MPI_Irecv(recv_buf, STR_LENGTH, MPI_CHAR, dstL, 0, MPI_COMM_WORLD, &req);
    MPI_Wait (&req, MPI_STATUS_IGNORE);
    #endif
  
  /* -- Replace color -- */

    sprintf (send_buf,"%s",recv_buf);
    if (rank == 0){
      printf ("Proc #%d, I've changed my color is %s\n", rank, send_buf);
    }
  }

  MPI_Finalize();
  return 0;
}