webamp/experiments/audioAbstraction/bufferSource.js

(function() {
  const invariant = (assertion, message) => {
    if (!assertion) {
      console.error(message);
    }
  };

  async function readFileAsArrayBuffer(file) {
    return new Promise((resolve, reject) => {
      const reader = new FileReader();
      reader.onload = function(e) {
        const arrayBuffer = e.target.result;
        resolve(arrayBuffer);
      };
      reader.onerror = function(e) {
        reject(e);
      };
      reader.readAsArrayBuffer(file);
    });
  }

  async function readUrlAsArrayBuffer(url) {
    return new Promise((resolve, reject) => {
      const oReq = new XMLHttpRequest();
      oReq.open("GET", url, true);
      oReq.responseType = "arraybuffer";

      oReq.onload = () => {
        const arrayBuffer = oReq.response; // Note: not oReq.responseText
        resolve(arrayBuffer);
      };

      oReq.onerror = e => {
        reject(e);
      };

      oReq.send(null);
      return true;
    });
  }

  const STATUS = {
    WAITING: "WAITING",
    PLAYING: "PLAYING",
    STOPPED: "STOPPED",
    PAUSED: "PAUSED"
  };

  class BufferSource extends window.Emitter {
    constructor(context, destination) {
      super();
      this._context = context;
      this._destination = destination;
      this._loop = false;
      this._buffer = null;
      this._source = null;
      this._status = STATUS.STOPPED;
      this._startTime = null;
      this._autoPlay = false;
      this._pausedAtTime = null;
      this._onEnded = this._onEnded.bind(this);
    }

    disconnect() {
      if (this._source != null) {
        this._source.disconnect();
      }
    }

    // Just adapt the callback into a promise.
    _decodeAudioData(buffer) {
      return new Promise((resolve, reject) => {
        this._context.decodeAudioData(buffer, resolve, reject);
      });
    }

    async loadFile(file) {
      this._setStatus(STATUS.WAITING);
      const arrayBuffer = await readFileAsArrayBuffer(file);
      this._buffer = await this._decodeAudioData(arrayBuffer);
      if (this._autoPlay) {
        this.play();
      }
    }

    async loadUrl(url) {
      this._setStatus(STATUS.WAITING);
      const arrayBuffer = await readUrlAsArrayBuffer(url);
      this._buffer = await this._decodeAudioData(arrayBuffer);
      if (this._autoPlay) {
        this.play();
      }
    }

    play() {
      switch (this._status) {
        case STATUS.WAITING:
        case STATUS.PLAYING:
        case STATUS.STOPPED:
          this._start(0);
          break;
        case STATUS.PAUSED:
          invariant(
            this._pausedAtTime != null,
            "Status is paused, but there is no _pausedAtTime"
          );
          this._start(this._pausedAtTime);
          break;
      }
    }

    pause() {
      this._pausedAtTime = this.getTimeElapsed();
      this._silence(STATUS.PAUSED);
    }

    stop() {
      this._silence(STATUS.STOPPED);
    }

    seekToTime(time) {
      time = Math.min(time, this.getDuration());
      time = Math.max(time, 0);
      this._start(time);
    }

    getStatus() {
      return this._status;
    }

    getDuration() {
      if (this._buffer == null) {
        return 0;
      }
      return this._buffer.duration;
    }

    getTimeElapsed() {
      switch (this._status) {
        case STATUS.PLAYING:
          invariant(
            this._startTime != null,
            "status is playing, but there is no _startTime"
          );
          return this._context.currentTime - this._startTime;
        case STATUS.STOPPED:
        case STATUS.WAITING:
          return 0;
        case STATUS.PAUSED:
          invariant(
            this._pausedAtTime != null,
            "Status is paused, but there is no _pausedAtTime"
          );
          return this._pausedAtTime;
      }
      throw new Error("Invalid status");
    }

    getNumberOfChannels() {
      if (this._buffer == null) {
        return null;
      }
      return this._buffer.numberOfChannels;
    }

    getSampleRate() {
      if (this._buffer == null) {
        return null;
      }
      return this._buffer.sampleRate;
    }

    getLoop() {
      return this._loop;
    }

    setLoop(shouldLoop) {
      this._loop = shouldLoop;
      if (this._source) {
        this._source.loop = this._loop;
      }
    }

    setAutoPlay(shouldAutoPlay) {
      this._autoPlay = shouldAutoPlay;
    }

    _start(position) {
      if (this._buffer == null) {
        return;
      }
      if (this._source) {
        // Does this work?
        this._source.disconnect();
        this._source = null;
      }
      this._source = this._context.createBufferSource();
      this._source.buffer = this._buffer;
      this._source.loop = this._loop;
      this._source.connect(this._destination);
      this._source.onended = this._onEnded;
      this._startTime = this._context.currentTime - position;
      this._setStatus(STATUS.PLAYING);
      this._source.start(0, position);
    }

    _silence(reason) {
      if (!reason) {
        throw new Error("Tried to silence the audio without a reason");
      }
      // We must always update the status before ending the audio, so that onEnded
      // can distinguish between audio that got to the end of the track, and audio
      // that the user stopped/paused
      this._setStatus(reason);
      if (this._source == null) {
        return;
      }
      this._source.stop(0);
      this._source = null;
    }

    _startMonitoringPosition() {
      this._nextPositionUpdate = setTimeout(() => {
        this.trigger("positionChange");
        this._startMonitoringPosition();
      }, 100);
    }

    _stopMonitoringPosition() {
      clearTimeout(this._nextPositionUpdate);
    }

    _setStatus(status) {
      this._status = status;
      if (status === STATUS.PLAYING) {
        this._startMonitoringPosition();
      } else {
        this._stopMonitoringPosition();
      }
      this.trigger("statusChange");
    }

    _onEnded() {
      if (this._status === STATUS.PLAYING) {
        this._setStatus(STATUS.STOPPED);
      }
    }
  }

  window.BufferSource = BufferSource;
  //export default BufferSource;
})();