class ChromeTtsEngine extends ChromeApi {
 static final JsObject _ttsEngine = chrome['ttsEngine'];

 ChromeTtsEngine._();

 bool get available => _ttsEngine != null;

 /**
  * Routes a TTS event from a speech engine to a client.
  * 
  * [event] The update event from the text-to-speech engine indicating the
  * status of this utterance.
  */
 void sendTtsEvent(int requestId, TtsEvent event) {
   if (_ttsEngine == null) _throwNotAvailable();

   _ttsEngine.callMethod('sendTtsEvent', [requestId, jsify(event)]);
 }

 /**
  * Called when the user makes a call to tts.speak() and one of the voices from
  * this extension's manifest is the first to match the options object.
  */
 Stream<OnSpeakEvent> get onSpeak => _onSpeak.stream;

 final ChromeStreamController<OnSpeakEvent> _onSpeak =
     new ChromeStreamController<OnSpeakEvent>.threeArgs(_ttsEngine, 'onSpeak', _createOnSpeakEvent);

 /**
  * Fired when a call is made to tts.stop and this extension may be in the
  * middle of speaking. If an extension receives a call to onStop and speech is
  * already stopped, it should do nothing (not raise an error). If speech is in
  * the paused state, this should cancel the paused state.
  */
 Stream get onStop => _onStop.stream;

 final ChromeStreamController _onStop =
     new ChromeStreamController.noArgs(_ttsEngine, 'onStop');

 /**
  * Optional: if an engine supports the pause event, it should pause the
  * current utterance being spoken, if any, until it receives a resume event or
  * stop event. Note that a stop event should also clear the paused state.
  */
 Stream get onPause => _onPause.stream;

 final ChromeStreamController _onPause =
     new ChromeStreamController.noArgs(_ttsEngine, 'onPause');

 /**
  * Optional: if an engine supports the pause event, it should also support the
  * resume event, to continue speaking the current utterance, if any. Note that
  * a stop event should also clear the paused state.
  */
 Stream get onResume => _onResume.stream;

 final ChromeStreamController _onResume =
     new ChromeStreamController.noArgs(_ttsEngine, 'onResume');

 void _throwNotAvailable() {
   throw new UnsupportedError("'chrome.ttsEngine' is not available");
 }
}