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

/* command line configurables */
int Ntrips;  /* -t <ntrips> */
int Verbose; /* -v */

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

    int i;
    int error;

    /* default values */
    Ntrips = 1;
    Verbose = 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], "-v"))
            Verbose = 1;
        else
            error = 1;

    } /* endfor */

    if (error && !my_id)
    {
        /* only Master prints usage message */
        fprintf(stderr, "\n\tusage: %s {-t <ntrips>} {-v}\n\n", argv[0]);
        fprintf(stderr, "where\n\n");
        fprintf(stderr,
	    "\t-t <ntrips>\t- Number of trips around the ring.  "
	    "Default value 1.\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() */

int main(int argc, char **argv)
{

    int numprocs, my_id, passed_num;
    int trip;
    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)
    {
        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, 1);


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

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

                printf("Master: end of trip %d of %d: "
		    "after receiving passed_num=%d "
		    "(should be =trip*numprocs=%d) from source=%d\n", 
		    trip, Ntrips, passed_num, trip*numprocs, numprocs-1);
            } /* 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, my_id-1);

                MPI_Recv(&passed_num,    /* buff   */
                        1,               /* count  */
                        MPI_INT,         /* type   */
                        my_id-1,         /* 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, my_id-1);

                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, (my_id+1)%numprocs);

                MPI_Send(&passed_num,       /* buff  */
                        1,                  /* count */
                        MPI_INT,            /* type  */
                        (my_id+1)%numprocs, /* 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, (my_id+1)%numprocs);
            } /* endfor */
        } /* endif */
    } 
    else
        printf("numprocs = %d, should be run with numprocs > 1\n", numprocs);

    MPI_Finalize();

    exit(0);

} /* end main() */