/*
 * noblank.c:
 *   a wrapper for applications and/or games that lack support
 *   for xscreensaver. deactivates every 60 seconds by default,
 *   tunable with the NOBLANK_INTERVAL env variable.
 *
 * Compiling:
 *   gcc noblank.c -o noblank
 *
 * Usage:
 *   noblank quake3 +disconnect +set fs_game arena
 *   noblank nwn
 *
 * Related:
 *   http://www.jwz.org/xscreensaver/faq.html#dvd
 *
 * Mike Hokenson <http://www.gozer.org/>
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <wait.h>
#include <unistd.h>

static int do_callback = 0;
static int do_exit = 0;

void sighandler(int sig)
{
  switch (sig) {
    case SIGALRM:
      do_callback = 1;
      break;
    case SIGCHLD:
      do_exit = 1;
      break;
    default:
      break;
  }
}

int main(int argc, char *argv[])
{
  int interval = 60;

  char *e;

  pid_t pid;

  if (argc < 2) {
    fprintf(stderr, "Usage: %s command [ arg ... ]\n", argv[0]);
    exit(1);
  }

  if ((e = getenv("NOBLANK_INTERVAL")) && *e) {
    int n = atoi(e);

    if (n > 0)
      interval = n;
  }

  argv++;
  argc--;

  pid = fork();

  switch (pid) {
    case 0:  /* child */
      if (execvp(*argv, argv) == -1) {
        fprintf(stderr, "Failed to execute '%s': %s\n", *argv, strerror(errno));
        usleep(25000); /* long enough for sighandler to be installed below */
        _exit(1);
      }

      _exit(0);
    case -1: /* error */
      fprintf(stderr, "Failed to create new process: %s\n", strerror(errno));
      exit(1);
    default: /* parent */
      break;
  }

  signal(SIGALRM, sighandler);
  signal(SIGCHLD, sighandler);

  alarm(interval);

  while (1) {
    struct timeval tv;

    if (do_exit)
      break;

    if (do_callback) {
      signal(SIGCHLD, SIG_IGN);
      system("xscreensaver-command -deactivate > /dev/null 2>&1");
      signal(SIGCHLD, sighandler);

      do_callback = 0;
      alarm(interval);

      if (kill(pid, 0))  /* check if the process has exited */
        break;
    }

    tv.tv_sec  = 0;
    tv.tv_usec = 25000;

    select(0, 0, NULL, NULL, &tv);
  }

  alarm(0);

  wait(NULL);

  exit(0);
}