Merge pull request #76 from kchadha/decode-sound-refactor

Refactor decodeSound function

src/index.js

@@ -15,6 +15,27 @@ const ADPCMSoundDecoder = require('./ADPCMSoundDecoder');
  * that handles global functionality, and AudioPlayers, belonging to individual sprites and clones.
  */
 
+/**
+ * Wrapper to ensure that audioContext.decodeAudioData is a promise
+ * @param {object} audioContext The current AudioContext
+ * @param {ArrayBuffer} buffer Audio data buffer to decode
+ * @return {Promise} A promise that resolves to the decoded audio
+ */
+const decodeAudioData = function (audioContext, buffer) {
+    // Check for newer promise-based API
+    if (audioContext.decodeAudioData.length === 1) {
+        return audioContext.decodeAudioData(buffer);
+    }
+    // Fall back to callback API
+    return new Promise((resolve, reject) => {
+        audioContext.decodeAudioData(buffer,
+            decodedAudio => resolve(decodedAudio),
+            error => reject(error)
+        );
+    });
+};
+
+
 class AudioPlayer {
     /**
      * Each sprite or clone has an audio player
@@ -189,46 +210,35 @@ class AudioEngine {
      * Store a reference to it the sound in the audioBuffers dictionary, indexed by soundId
      * @param  {object} sound - an object containing audio data and metadata for a sound
      * @property {Buffer} data - sound data loaded from scratch-storage.
-     * @property {string} format - format type, either empty or adpcm.
      * @returns {?Promise} - a promise which will resolve to the soundId if decoded and stored.
      */
     decodeSound (sound) {
-        const soundId = uid();
-        let loaderPromise = null;
-
         // Make a copy of the buffer because decoding detaches the original buffer
-        const bufferCopy = sound.data.buffer.slice(0);
+        const bufferCopy1 = sound.data.buffer.slice(0);
 
-        switch (sound.format) {
+        const soundId = uid();
-        case '':
+        // Partially apply updateSoundBuffer function with the current
-            // Check for newer promise-based API
+        // soundId so that it's ready to be used on successfully decoded audio
-            if (this.audioContext.decodeAudioData.length === 1) {
+        const addDecodedAudio = this.updateSoundBuffer.bind(this, soundId);
-                loaderPromise = this.audioContext.decodeAudioData(bufferCopy);
+
-            } else {
+        // Attempt to decode the sound using the browser's native audio data decoder
-                // Fall back to callback API
+        // If that fails, attempt to decode as ADPCM
-                loaderPromise = new Promise((resolve, reject) => {
+        return decodeAudioData(this.audioContext, bufferCopy1).then(
-                    this.audioContext.decodeAudioData(bufferCopy,
+            addDecodedAudio,
-                        decodedAudio => resolve(decodedAudio),
+            () => {
-                        error => reject(error)
+                // The audio context failed to parse the sound data
+                // we gave it, so try to decode as 'adpcm'
+
+                // First we need to create another copy of our original data
+                const bufferCopy2 = sound.data.buffer.slice(0);
+                // Try decoding as adpcm
+                return (new ADPCMSoundDecoder(this.audioContext)).decode(bufferCopy2)
+                    .then(
+                        addDecodedAudio,
+                        error => {
+                            log.warn('audio data could not be decoded', error);
+                        }
                     );
-                });
-            }
-            break;
-        case 'adpcm':
-            loaderPromise = (new ADPCMSoundDecoder(this.audioContext)).decode(bufferCopy);
-            break;
-        default:
-            return log.warn('unknown sound format', sound.format);
-        }
-
-        const storedContext = this;
-        return loaderPromise.then(
-            decodedAudio => {
-                storedContext.audioBuffers[soundId] = decodedAudio;
-                return soundId;
-            },
-            error => {
-                log.warn('audio data could not be decoded', error);
             }
         );
     }
@@ -243,12 +253,14 @@ class AudioEngine {
     }
 
     /**
-     * Update the in-memory audio buffer to a new one by soundId.
+     * Add or update the in-memory audio buffer to a new one by soundId.
      * @param {!string} soundId - the id of the sound buffer to update.
      * @param {AudioBuffer} newBuffer - the new buffer to swap in.
+     * @return {string} The uid of the sound that was updated or added
      */
     updateSoundBuffer (soundId, newBuffer) {
         this.audioBuffers[soundId] = newBuffer;
+        return soundId;
     }
 
     /**