abstract class Timer {
  /**
   * Creates a new timer. The [callback] callback is invoked after
   * [milliSeconds] milliseconds.
   */
  factory Timer(int milliSeconds, void callback(Timer timer)) {
    if (_TimerFactory._factory == null) {
      throw new UnsupportedOperationException("Timer interface not supported.");
    }
    return _TimerFactory._factory(milliSeconds, callback, false);
  }

  /**
   * Creates a new repeating timer. The [callback] is invoked every
   * [milliSeconds] millisecond until cancelled.
   */
  factory Timer.repeating(int milliSeconds, void callback(Timer timer)) {
    if (_TimerFactory._factory == null) {
      throw new UnsupportedOperationException("Timer interface not supported.");
    }
    return _TimerFactory._factory(milliSeconds, callback, true);
  }

  /**
   * Cancels the timer.
   */
  void cancel();
}