#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/time.h>
#include <stdlib.h>
#include <string.h>

#define BUFLEN sizeof(struct timeval)
#define PORT 9876

static int sock_fd, slen;

void diep(char * s)
{
    perror(s);
    exit(1);
}

static long long time_diff(struct timeval * one, struct timeval * two)
{
    long long t1 = ((long long) one->tv_sec) * 1000000
        + (long long) one->tv_usec;
    long long t2 = ((long long) two->tv_sec) * 1000000
        + (long long) two->tv_usec;
    return t1 - t2;
}

void * thread(void * arg)
{
    struct sockaddr_in si_other;
    char time_str[100];
    struct timeval tv_msg, tv_now, tv_last;
    for (;;)
    {
        if (recvfrom(sock_fd, &tv_msg, BUFLEN, 0,
                    (struct sockaddr *) &si_other, &slen) == -1)
            diep("recvfrom()");
        gettimeofday(&tv_now, NULL);
        struct tm * lt = localtime(&tv_now.tv_sec);
        strftime(time_str, 100, "%F %T", lt);
        printf("Rcv: %s, rtt: %lld, elapsed: %lld\n",
                time_str,
                time_diff(&tv_now, &tv_msg),
                time_diff(&tv_now, &tv_last));
        tv_last.tv_sec = tv_now.tv_sec;
        tv_last.tv_usec = tv_now.tv_usec;
    }
}

int main(int argc, char * argv[])
{
    int interval;
    struct timeval tv;
    struct sockaddr_in si_other;
    if (argc != 3)
    {
        printf("Usage: client server-address msec-interval\n");
        exit(2);
    }
    interval = atoi(argv[2]) * 1000;

    slen = sizeof(si_other);

    if ((sock_fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
        diep("socket");

    memset((char *) &si_other, 0, sizeof(si_other));
    si_other.sin_family = AF_INET;
    si_other.sin_port = htons(PORT);
    inet_aton(argv[1], &si_other.sin_addr);
#if 0
    if (bind(sock_fd, (struct sockaddr *) &si_other, sizeof(si_other)) == -1)
        diep("bind");
#endif

    pthread_t t;
    if (pthread_create(&t, NULL, thread, NULL) != 0)
        diep("pthread_create()");

    usleep(100000);
    for (;;)
    {
        gettimeofday(&tv, NULL);
        if (sendto(sock_fd, &tv, BUFLEN, 0,
                    (struct sockaddr *) &si_other, slen) == -1)
            diep("sendto()");
        usleep(interval);
    }

    close(sock_fd);
    return 0;
}