static long timer_nextFireTime(O timer, long now) {
  long best = 0;
  for (O entry : unnull((Collection) getOpt(timer, 'entries))) {
    Long firstTime = cast getOpt(entry, 'firstTime);
    Long period = cast getOpt(entry, 'period);
    if (firstTime != null && period != null)
      if (now >= firstTime) {
        long fireTime = now + period-((now - firstTime) % period);
        if (best == 0 || fireTime < best) best = fireTime;
      }
  }
  ret best;
}