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

int main (int argc, char *argv[])
{
  int id, np;
  char name[MPI_MAX_PROCESSOR_NAME];
  char message[128], filename[128], line[128];
  int namelen;
  MPI_Status status;
  int i, st;
  FILE *fid;
  void nodesused ();

  MPI_Init (&argc, &argv);

  MPI_Comm_size (MPI_COMM_WORLD, &np);
  MPI_Comm_rank (MPI_COMM_WORLD, &id);
  MPI_Get_processor_name (name, &namelen);

  /* ------------------------------------------------------------------- */
  /* The following code prints the name of the run directory: */

  if (id == 0)
  {
    printf ("\n");
    printf ("Running in directory\n");
    system ("/bin/pwd");
    printf ("\n");
    fflush (stdout);
  }

  /* ------------------------------------------------------------------- */
  /* The following code tests MPI_Bcast: */

  sprintf (message, "This is a message from Process %2d to all", id);
  MPI_Bcast (message, 128, MPI_CHAR, 0, MPI_COMM_WORLD);
  printf ("[%2d] %s\n", id, message);
  fflush (stdout);

  /* ------------------------------------------------------------------- */
  /* The following code tests MPI_Send / MPI_Recv: */

  nodesused ();

  /* ------------------------------------------------------------------- */
  /* The following code tests whether every process can read the same
     input file from the run directory: */

  sprintf (filename, "testio.in");
  fid = fopen (filename, "r");
  if (fid == NULL)
  {
    fprintf (stderr, "Problem opening input file %s. Aborting.\n", filename);
    MPI_Abort (MPI_COMM_WORLD, 1);
  }

  fgets (line, sizeof(line), fid);
  printf ("[%2d] Line from input file: %s\n", id, line);
  fflush (stdout);

  fclose (fid);

  /* ------------------------------------------------------------------- */
  /* The following code tests whether each process can write to a file
     with filename testio-p<id>.out, where <id> is its own process number,
     and whether these files end up in the run directory: */

  sprintf (filename, "testio-p%2.2d.out", id);
  fid = fopen (filename, "w");
  if (fid == NULL)
  {
    fprintf (stderr, "Problem opening input file %s. Aborting.\n", filename);
    MPI_Abort (MPI_COMM_WORLD, 1);
  }

  sprintf (message, "Output filename = %s", filename);
  st = fprintf (fid, "[%2d] Message to output file: %s\n", id, message);
  if (st < 0)
  {
    fprintf (stderr, "Problem writing line to file. Aborting.\n");
    MPI_Abort (MPI_COMM_WORLD, 2);
  }

  /* print message to screen in case of success: */
  printf ("[%2d] Message successfully printed to file %s\n", id, filename);
  fflush (stdout);

  fclose (fid);


  /* ------------------------------------------------------------------- */

  MPI_Finalize ();

  return (0);
}

/* --------------------------------------------------------------------- */

void nodesused (void)
{
  int id, np;
  char name[MPI_MAX_PROCESSOR_NAME];
  int namelen;
  MPI_Status status;
  int i;
  char message[128];

  MPI_Comm_size (MPI_COMM_WORLD, &np);
  MPI_Comm_rank (MPI_COMM_WORLD, &id);
  MPI_Get_processor_name (name, &namelen);

  sprintf (message, "Process %2d out of %2d running on host %s", id, np, name);
  /* uncomment for testing: */
  /* printf ("[%2d] %s\n", id, message); */
  if (id == 0)
  {
    printf ("\n");
    /* print own message first: */
    printf ("[%2d] %s\n", id, message);
    /* receive and print messages from other processes: */
    for (i = 1; i < np; i++)
    {
      MPI_Recv (message, 128, MPI_CHAR, i, i, MPI_COMM_WORLD, &status);
      printf ("[%2d] %s\n", id, message);
    }
    fflush (stdout);
  }
  else /* (id > 0) */
  {
    MPI_Send (message, strlen(message)+1, MPI_CHAR, 0, id, MPI_COMM_WORLD);
  }
}

/* --------------------------------------------------------------------- */