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

/* command line configurables */
int Ntrips;        /* -t <ntrips> */
int Verbose;       /* -v */
int Reverse;       /* -r */
int Alternate;     /* -a */

int parse_command_line_args(int argc, char **argv, int my_id)
{

int i;
int error;

    /* default values */
    Ntrips = 10000;
    Verbose = 0;
    Reverse = 0;

    for (i = 1, error = 0; !error && i < argc; i ++)
    {
	if (!strcmp(argv[i], "-t"))
	{
	    if (i + 1 < argc && (Ntrips = atoi(argv[i+1])) > 0)
		i ++;
	    else
		error = 1;
	}
	else if (!strcmp(argv[i], "-a"))
	    Alternate = 1; 
	else if (!strcmp(argv[i], "-r"))
	    Reverse = 1; 
	else if (!strcmp(argv[i], "-v"))
	    Verbose = 1; 
	else
	    error = 1;

    } /* endfor */

    if (error && !my_id)
    {
	/* only Master prints usage message */
	fprintf(stderr, "\n\tusage: %s {-t <ntrips>} {-r} {-a} {-v}\n\n", 
	    argv[0]);
	fprintf(stderr, "where\n\n");
	fprintf(stderr,
	    "\t-v <ntrips>\t- Number of trips around the ring.  "
	    "Default value 1.\n");
	fprintf(stderr,
	    "\t-r\t\t- Reverse direction. By default first trip's direction"
	    " is 0->1->2 etc.  '-r' reverses direction.\n");
	fprintf(stderr,
	    "\t-a\t\t- Alternate direction. When ntrips > 1 alternate the"
	    "direction of each trip. Default is no alternate.\n");
	fprintf(stderr,
	    "\t-v\t\t- Verbose.  Master and all slaves log each step. \n");
	fprintf(stderr, "\t\t\t  Default value is FALSE.\n\n");
    } /* endif */

    return error;

} /* end parse_command_line_args() */

main(int argc, char **argv)
{

    int numprocs, my_id, passed_num;
    int trip;
    int dest_f, src_f;
    int dest_r, src_r;
    int *dest, *src;
    MPI_Status status;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &my_id);

    if (parse_command_line_args(argc, argv, my_id))
    {
	MPI_Finalize();
	exit(1);
    } /* endif */

    if (Verbose)
	printf("my_id %d numprocs %d\n", my_id, numprocs);

    if (numprocs > 1)
    {
	dest_f = src_r  = (my_id+1) % numprocs;
	src_f  = dest_r = (my_id ? my_id-1 : numprocs-1);

	dest = (Reverse ? &dest_r : &dest_f);
	src  = (Reverse ? &src_r  : &src_f);

	if (my_id == 0)
	{
	    /* I am the Master */

	    passed_num = 0;
	    for (trip = 1; trip <= Ntrips; trip ++)
	    {
		passed_num ++;

		if (Verbose)
		    printf("Master: starting trip %d of %d: before sending "
			"num=%d to dest=%d\n", 
			trip, Ntrips, passed_num, *dest);
		MPI_Send(&passed_num,    /* buff  */
			1,               /* count */
			MPI_INT,         /* type  */
			*dest,           /* dest  */
			0,               /* tag   */
			MPI_COMM_WORLD); /* comm  */
     
		if (Verbose)
		    printf("Master: inside trip %d of %d: before receiving "
			"from source=%d\n", 
			trip, Ntrips, *src);

		MPI_Recv(&passed_num,    /* buff   */
			1,               /* count  */
			MPI_INT,         /* type   */
			*src,            /* source */
			0,               /* tag    */
			MPI_COMM_WORLD,  /* comm   */
			&status);        /* status */

		printf("Master: initial direction=%s: end of trip %d of %d: "
		    "after receiving passed_num=%d "
		    "(should be =trip*numprocs=%d) from source=%d\n", 
		    (Reverse ? "reverse" : "forward"), trip, Ntrips, 
		    passed_num, trip*numprocs, *src);

		if (Alternate)
		{
		    dest = (dest == &dest_f ? &dest_r : &dest_f);
		    src  = (src  == &src_f  ? &src_r  : &src_f );
		} /* endif */

	    } /* endfor */ 
	}
	else
	{
	    /* I am a Slave */

	    for (trip = 1; trip <= Ntrips; trip ++)
	    {
		if (Verbose)
		    printf("Slave %d: top of trip %d of %d: before receiving "
			"from source=%d\n", 
			my_id, trip, Ntrips, *src);

		MPI_Recv(&passed_num,    /* buff   */
			1,               /* count  */
			MPI_INT,         /* type   */
			*src,            /* source */
			0,               /* tag    */
			MPI_COMM_WORLD,  /* comm   */
			&status);        /* status */

		if (Verbose)
		    printf("Slave %d: inside trip %d of %d: after receiving "
			"passed_num=%d from source=%d\n", 
			my_id, trip, Ntrips, passed_num, *src);

		passed_num ++;

		if (Verbose)
		    printf("Slave %d: inside trip %d of %d: before sending "
			"passed_num=%d to dest=%d\n", 
			my_id, trip, Ntrips, passed_num, *dest);

		MPI_Send(&passed_num,    /* buff  */
			1,               /* count */
			MPI_INT,         /* type  */
			*dest,           /* dest  */
			0,               /* tag   */
			MPI_COMM_WORLD); /* comm  */

		if (Verbose)
		    printf("Slave %d: bottom of trip %d of %d: after send to "
			"dest=%d\n",
			my_id, trip, Ntrips, *dest);

		if (Alternate)
		{
		    dest = (dest == &dest_f ? &dest_r : &dest_f);
		    src  = (src  == &src_f  ? &src_r  : &src_f );
		} /* endif */
	    } /* endfor */
	} /* endif */
    } 
    else
	printf("numprocs = %d, should be run with numprocs > 1\n", numprocs);

    MPI_Finalize();

} /* end main() */