sdk/tools/dom/templates/html/impl/impl_AudioContext.darttemplate

// Copyright (c) 2012, 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 web_audio;

$(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
$!MEMBERS
  factory AudioContext() => JS('AudioContext',
      'new (window.AudioContext || window.webkitAudioContext)()');

  GainNode createGain() {
    if (JS('bool', '#.createGain !== undefined', this)) {
      return JS('GainNode', '#.createGain()', this);
    } else {
      return JS('GainNode', '#.createGainNode()', this);
    }
  }

  ScriptProcessorNode createScriptProcessor([int$NULLABLE bufferSize,
      int$NULLABLE numberOfInputChannels,
      int$NULLABLE numberOfOutputChannels]) {
    var function = JS(
        '=Object',
        '#.createScriptProcessor || '
        '#.createJavaScriptNode',
        this,
        this);
    if (numberOfOutputChannels != null) {
      return JS('ScriptProcessorNode', '#.call(#, #, #, #)', function, this,
          bufferSize, numberOfInputChannels, numberOfOutputChannels);
    } else if (numberOfInputChannels != null) {
      return JS('ScriptProcessorNode', '#.call(#, #, #)', function, this,
          bufferSize, numberOfInputChannels);
    } else if (bufferSize != null) {
      return JS(
          'ScriptProcessorNode', '#.call(#, #)', function, this, bufferSize);
    } else {
      return JS(
          'ScriptProcessorNode', '#.call(#)', function, this);
    }
  }

  Future<AudioBuffer> decodeAudioData(ByteBuffer audioData,
      [DecodeSuccessCallback$NULLABLE successCallback,
      DecodeErrorCallback$NULLABLE errorCallback]) {
    // Both callbacks need to be provided if they're being used.
    assert((successCallback == null) == (errorCallback == null));
    // `decodeAudioData` can exist either in the older callback syntax or the
    // newer `Promise`-based syntax that also accepts callbacks. In the former,
    // we synthesize a `Future` to be consistent.
    // For more details:
    // https://developer.mozilla.org/en-US/docs/Web/API/BaseAudioContext/decodeAudioData
    // https://www.w3.org/TR/webaudio/#dom-baseaudiocontext-decodeaudiodata
    final completer = Completer<Object>();
    var errorInCallbackIsNull = false;

    void success(AudioBuffer decodedData) {
      completer.complete(decodedData);
      successCallback$NULLASSERT.call(decodedData);
    }

    final nullErrorString =
        '[AudioContext.decodeAudioData] completed with a null error.';

    void error(DomException$NULLABLE error) {
      // Safari has a bug where it may return null for the error callback. In
      // the case where the Safari version still returns a `Promise` and the
      // error is not null after the `Promise` is finished, the error callback
      // is called instead in the `Promise`'s `catch` block. Otherwise, and in
      // the case where a `Promise` is not returned by the API at all, the
      // callback never gets called (for backwards compatibility, it can not
      // accept null). Instead, the `Future` completes with a custom string,
      // indicating that null was given.
      // https://github.com/mdn/webaudio-examples/issues/5
      if (error != null) {
        // Note that we `complete` and not `completeError`. This is to make sure
        // that errors in the `Completer` are not thrown if the call gets back
        // a `Promise`.
        completer.complete(error);
        errorCallback$NULLASSERT.call(error);
      } else {
        completer.complete(nullErrorString);
        errorInCallbackIsNull = true;
      }
    }

    var decodeResult;
    if (successCallback == null) {
      decodeResult =
          JS("creates:AudioBuffer;", "#.decodeAudioData(#)", this, audioData);
    } else {
      decodeResult = JS(
          "creates:AudioBuffer;",
          "#.decodeAudioData(#, #, #)",
          this,
          audioData,
          convertDartClosureToJS(success, 1),
          convertDartClosureToJS(error, 1));
    }

    if (decodeResult != null) {
      // Promise-based syntax.
      return promiseToFuture<AudioBuffer>(decodeResult).catchError((error) {
        // If the error was null in the callback, but no longer is now that the
        // `Promise` is finished, call the error callback. If it's still null,
        // throw the error string. This is to handle the aforementioned bug in
        // Safari.
        if (errorInCallbackIsNull) {
          if (error != null) {
            errorCallback?.call(error);
          } else {
            throw nullErrorString;
          }
        }
        throw error;
      });
    }

    // Callback-based syntax. We use the above completer to synthesize a
    // `Future` from the callback values. Since we don't use `completeError`
    // above, `then` is used to simulate an error.
    return completer.future.then((value) {
      if (value is AudioBuffer) return value;
      throw value;
    });
  }
}