tools/dom/src/EventStreamProvider.dart

// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of html;

/**
 * Adapter for exposing DOM events as Dart streams.
 */
class _EventStream<T extends Event> extends Stream<T> {
  final EventTarget _target;
  final String _eventType;
  final bool _useCapture;

  _EventStream(this._target, this._eventType, this._useCapture);

  // DOM events are inherently multi-subscribers.
  Stream<T> asBroadcastStream() => this;
  bool get isBroadcast => true;

  StreamSubscription<T> listen(void onData(T event),
      { void onError(AsyncError error),
      void onDone(),
      bool unsubscribeOnError}) {

    return new _EventStreamSubscription<T>(
        this._target, this._eventType, onData, this._useCapture);
  }
}

class _EventStreamSubscription<T extends Event> extends StreamSubscription<T> {
  int _pauseCount = 0;
  EventTarget _target;
  final String _eventType;
  var _onData;
  final bool _useCapture;

  _EventStreamSubscription(this._target, this._eventType, this._onData,
      this._useCapture) {
    _tryResume();
  }

  void cancel() {
    if (_canceled) {
      throw new StateError("Subscription has been canceled.");
    }

    _unlisten();
    // Clear out the target to indicate this is complete.
    _target = null;
    _onData = null;
  }

  bool get _canceled => _target == null;

  void onData(void handleData(T event)) {
    if (_canceled) {
      throw new StateError("Subscription has been canceled.");
    }
    // Remove current event listener.
    _unlisten();

    _onData = handleData;
    _tryResume();
  }

  /// Has no effect.
  void onError(void handleError(AsyncError error)) {}

  /// Has no effect.
  void onDone(void handleDone()) {}

  void pause([Future resumeSignal]) {
    if (_canceled) {
      throw new StateError("Subscription has been canceled.");
    }
    ++_pauseCount;
    _unlisten();

    if (resumeSignal != null) {
      resumeSignal.whenComplete(resume);
    }
  }

  bool get _paused => _pauseCount > 0;

  void resume() {
    if (_canceled) {
      throw new StateError("Subscription has been canceled.");
    }
    if (!_paused) {
      throw new StateError("Subscription is not paused.");
    }
    --_pauseCount;
    _tryResume();
  }

  void _tryResume() {
    if (_onData != null && !_paused) {
      _target.$dom_addEventListener(_eventType, _onData, _useCapture);
    }
  }

  void _unlisten() {
    if (_onData != null) {
      _target.$dom_removeEventListener(_eventType, _onData, _useCapture);
    }
  }
}


/**
 * A factory to expose DOM events as Streams.
 */
class EventStreamProvider<T extends Event> {
  final String _eventType;

  const EventStreamProvider(this._eventType);

  /**
   * Gets a [Stream] for this event type, on the specified target.
   *
   * This may be used to capture DOM events:
   *
   *     Element.keyDownEvent.forTarget(element, useCapture: true).listen(...);
   *
   * Or for listening to an event which will bubble through the DOM tree:
   *
   *     MediaElement.pauseEvent.forTarget(document.body).listen(...);
   *
   * See also:
   *
   * [addEventListener](http://docs.webplatform.org/wiki/dom/methods/addEventListener)
   */
  Stream<T> forTarget(EventTarget e, {bool useCapture: false}) {
    return new _EventStream(e, _eventType, useCapture);
  }

  /**
   * Gets the type of the event which this would listen for on the specified
   * event target.
   *
   * The target is necessary because some browsers may use different event names
   * for the same purpose and the target allows differentiating browser support.
   */
  String getEventType(EventTarget target) {
    return _eventType;
  }
}

/**
 * A factory to expose DOM events as streams, where the DOM event name has to
 * be determined on the fly (for example, mouse wheel events).
 */
class _CustomEventStreamProvider<T extends Event>
    implements EventStreamProvider<T> {

  final _eventTypeGetter;
  const _CustomEventStreamProvider(this._eventTypeGetter);

  Stream<T> forTarget(EventTarget e, {bool useCapture: false}) {
    return new _EventStream(e, _eventTypeGetter(e), useCapture);
  }

  String getEventType(EventTarget target) {
    return _eventTypeGetter(target);
  }
}