int MPI_Comm_size(MPI_Comm comm, int *size) {
  *size = comm->nprocs;
  return 0;
}

int MPI_Comm_rank(MPI_Comm comm, int *rank) {
  // this only works for MPI_COMM_WORLD.
  // for multiple communicators, you will need 
  // a map (array) from PID to rank for each comm
  *rank = __rank;
  return 0;
}

int MPI_Send(void *buf, int count, MPI_Datatype datatype,
             int dest, int tag, MPI_Comm comm) {
  $atom {
    int size;
    
    switch (datatype) {
    case MPI_INT:
      buf = (int*)buf;
      size = count*sizeof(int); 
      break;
    case MPI_FLOAT:
      buf = (float*)buf;
      size = count*sizeof(float);
      break;
    case MPI_DOUBLE:
      buf = (double*)buf;
      size = count*sizeof(double);     
      break;
    case MPI_CHAR:
      buf = (char*)buf;
      size = count*sizeof(char);
      break;
    default:
      printf("Unsupported datatype %d\n", datatype);
      $assert $false;    
    }
    $message out = $message_pack(__rank, dest, tag, buf, size);
    $comm_enqueue(comm, out);
  }
  return 0;
}

int MPI_Recv(void *buf, int count, MPI_Datatype datatype,
             int source, int tag, MPI_Comm comm, MPI_Status *status) {
  $message in = $comm_dequeue(comm, source, __rank, tag);
  $atom {
    int size;
    
    switch (datatype) {
    case MPI_INT:
      buf = (int*)buf;
      size = count*sizeof(int); 
      break;
    case MPI_FLOAT:
      buf = (float*)buf;
      size = count*sizeof(float);
      break;
    case MPI_DOUBLE:
      buf = (double*)buf;
      size = count*sizeof(double);     
      break;
    case MPI_CHAR:
      buf = (char*)buf;
      size = count*sizeof(char);
      break;
    default:
      printf("Unsupported datatype %d\n", datatype);
      $assert $false;    
    }
    $message_unpack(in, buf, size);
    if (status != MPI_STATUS_IGNORE) {
      status->MPI_SOURCE = in.source;
      status->MPI_TAG = in.tag;
      status->size = in.size;
    }
  }
  return 0;
}

$when (__start);