/* 
 * usage: random-spair <# processes> <# messages>
 */

#include <stdio.h>
#include <poll.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/tcp.h>
#include <fcntl.h>
#include <netdb.h>


int main(int argc, char *argv[]) {
    int i, j, n, cnt, pid, rank, dest;
    int lsock;
    char data;
    int port = 11100;
    
    cnt = atoi(argv[1]);
    n = atoi(argv[2]);

    {
        int socks[cnt-1];    
        struct pollfd pfds[cnt-1];
        int spairs[2*cnt*cnt];    
        
        
        for (i=0; i<2*cnt*cnt; i+=2) {
            socketpair(AF_UNIX, SOCK_STREAM, 0, spairs+i);
        }   
        
        /* Create processes */
        rank = 0;
        for (i=1; i<cnt; i++) {
            pid = fork();
            if (pid == 0) {
                rank=cnt-i;
                break;    
            }
        }

        
        /* Assign sockets */
        j=0;
        for (i=0; i<cnt; i++) {
            if (i != rank) {
                if (i < rank) {
                    socks[j] = spairs[2*(i*cnt+rank)];                
                } else {
                    socks[j] = spairs[2*(rank*cnt+i)+1];                
                }
                pfds[j].fd = socks[j];
                pfds[j].events = POLLIN;
                j++;
            }
        }
                
        srandom(rank);        
        
        /* Write startup messages */
        if (rank < n) {
            dest = random()%(cnt-1);
            if (write(socks[dest], &data, 1) == -1) {
                perror("write 1");                            
            }
        }

        /* Receive and forward messages to random destinations */
        while (1) {
            poll(pfds, cnt-1, -1);
            j = 0;
            for (i=0; i<cnt-1; i++) {
                if (pfds[i].revents != 0) {
                    if (read(pfds[i].fd, &data, 1) == -1) {
                        perror("read");                            
                    }
                    j++;
                }
            }
            
            for (i=0; i<j; i++) {
                dest = random()%(cnt-1);
                if (write(socks[dest], &data, 1) == -1) {
                    perror("write 2");                            
                }
            }
        }
    }    
    return 0;
}