#NOT MY CODE
# Video Tutorial Can Be Seen Here: https://www.youtube.com/watch?v=Iv8vQDFJp4E

#define SINGLE_INSTANCE_PORT 38273

static void ensure_single_instance(void);

ensure_single_instance();

static void ensure_single_instance(void)
{
    static BOOL local_bind = TRUE;
    struct sockaddr_in addr;
    int opt = 1;

    if ((fd_ctrl = socket(AF_INET, SOCK_STREAM, 0)) == -1)
        return;
    setsockopt(fd_ctrl, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof (int));
    fcntl(fd_ctrl, F_SETFL, O_NONBLOCK | fcntl(fd_ctrl, F_GETFL, 0));

    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = local_bind ? (INET_ADDR(127,0,0,1)) : LOCAL_ADDR;
    addr.sin_port = htons(SINGLE_INSTANCE_PORT);

    // Try to bind to the control port
    errno = 0;
    if (bind(fd_ctrl, (struct sockaddr *)&addr, sizeof (struct sockaddr_in)) == -1)
    {
        if (errno == EADDRNOTAVAIL && local_bind)
            local_bind = FALSE;
#ifdef DEBUG
        printf("[main] Another instance is already running (errno = %d)! Sending kill request...\r\n", errno);
#endif

        // Reset addr just in case
        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = INADDR_ANY;
        addr.sin_port = htons(SINGLE_INSTANCE_PORT);

        if (connect(fd_ctrl, (struct sockaddr *)&addr, sizeof (struct sockaddr_in)) == -1)
        {
#ifdef DEBUG
            printf("[main] Failed to connect to fd_ctrl to request process termination\n");
#endif
        }
        
        sleep(5);
        close(fd_ctrl);
        killer_kill_by_port(htons(SINGLE_INSTANCE_PORT));
        ensure_single_instance(); // Call again, so that we are now the control
    }
    else
    {
        if (listen(fd_ctrl, 1) == -1)
        {
#ifdef DEBUG
            printf("[main] Failed to call listen() on fd_ctrl\n");
            close(fd_ctrl);
            sleep(5);
            killer_kill_by_port(htons(SINGLE_INSTANCE_PORT));
            ensure_single_instance();
#endif
        }
#ifdef DEBUG
        printf("[main] We are the only process on this system!\n");
#endif
    }
}