function Downloader() {
  this.isActive = false;
  this.realtime = false;
  this.chunkStart = 0;
  this.chunkSize = 0;
  this.totalLength = 0;
  this.chunkTimeout = 1000;
  this.url = null;
  this.callback = null;
  this.eof = false;
  this.setDownloadTimeoutCallback = null;
}

Downloader.prototype.setDownloadTimeoutCallback = function (callback) {
  this.setDownloadTimeoutCallback = callback;
  return this;
};

Downloader.prototype.reset = function () {
  this.chunkStart = 0;
  this.totalLength = 0;
  this.eof = false;
  return this;
};

Downloader.prototype.setRealTime = function (_realtime) {
  this.realtime = _realtime;
  return this;
};

Downloader.prototype.setChunkSize = function (_size) {
  this.chunkSize = _size;
  return this;
};

Downloader.prototype.setChunkStart = function (_start) {
  this.chunkStart = _start;
  this.eof = false;
  return this;
};

Downloader.prototype.setInterval = function (_timeout) {
  this.chunkTimeout = _timeout;
  return this;
};

Downloader.prototype.setUrl = function (_url) {
  this.url = _url;
  return this;
};

Downloader.prototype.setCallback = function (_callback) {
  this.callback = _callback;
  return this;
};

Downloader.prototype.isStopped = function () {
  return !this.isActive;
};

Downloader.prototype.getFileLength = function () {
  return this.totalLength;
};

Downloader.prototype.getFile = function () {
  var dl = this;
  if (dl.totalLength && this.chunkStart >= dl.totalLength) {
    dl.eof = true;
  }
  if (dl.eof === true) {
    Log.info('Downloader', 'File download done.');
    this.callback(null, true);
    return;
  }
  var xhr = new XMLHttpRequest();
  xhr.open('GET', this.url, true);
  xhr.responseType = 'arraybuffer';
  var range = null;
  xhr.start = this.chunkStart;
  var maxRange;
  if (this.chunkStart + this.chunkSize < Infinity) {
    range = 'bytes=' + this.chunkStart + '-';
    maxRange = this.chunkStart + this.chunkSize - 1;
    /* if the file length is known we limit the max range to that length */
    /*if (dl.totalLength !== 0) {
			maxRange = Math.min(maxRange, dl.totalLength);
		}*/
    range += maxRange;
    xhr.setRequestHeader('Range', range);
  }
  xhr.onerror = function (e) {
    dl.callback(null, false, true);
  };
  xhr.onreadystatechange = function (e) {
    if (xhr.status == 404) {
      dl.callback(null, false, true);
    }
    if (
      (xhr.status == 200 || xhr.status == 206 || xhr.status == 304 || xhr.status == 416) &&
      xhr.readyState == this.DONE
    ) {
      var rangeReceived = xhr.getResponseHeader('Content-Range');
      Log.info('Downloader', 'Received data range: ' + rangeReceived);
      /* if the length of the file is not known, we get it from the response header */
      if (!dl.totalLength && rangeReceived) {
        var sizeIndex;
        sizeIndex = rangeReceived.indexOf('/');
        if (sizeIndex > -1) {
          dl.totalLength = +rangeReceived.slice(sizeIndex + 1);
        }
      }
      dl.eof =
        xhr.response.byteLength !== dl.chunkSize || xhr.response.byteLength === dl.totalLength;
      var buffer = xhr.response;
      buffer.fileStart = xhr.start;
      if (!buffer.fileStart) {
        // IE does not support adding properties to an ArrayBuffer generated by XHR
        buffer = buffer.slice(0);
        buffer.fileStart = xhr.start;
      }
      dl.callback(buffer, dl.eof);
      if (dl.isActive === true && dl.eof === false) {
        var timeoutDuration = 0;
        if (!dl.realtime) {
          timeoutDuration = dl.chunkTimeout;
        } else {
          timeoutDuration = computeWaitingTimeFromBuffer(video);
        }
        if (dl.setDownloadTimeoutCallback) dl.setDownloadTimeoutCallback(timeoutDuration);
        Log.info(
          'Downloader',
          'Next download scheduled in ' + Math.floor(timeoutDuration) + ' ms.',
        );
        dl.timeoutID = window.setTimeout(dl.getFile.bind(dl), timeoutDuration);
      } else {
        /* end of file */
        dl.isActive = false;
      }
    }
  };
  if (dl.isActive) {
    Log.info('Downloader', 'Fetching ' + this.url + (range ? ' with range: ' + range : ''));
    xhr.send();
  }
};

Downloader.prototype.start = function () {
  Log.info('Downloader', 'Starting file download');
  this.chunkStart = 0;
  this.resume();
  return this;
};

Downloader.prototype.resume = function () {
  Log.info('Downloader', 'Resuming file download');
  this.isActive = true;
  if (this.chunkSize === 0) {
    this.chunkSize = Infinity;
  }
  this.getFile();
  return this;
};

Downloader.prototype.stop = function () {
  Log.info('Downloader', 'Stopping file download');
  this.isActive = false;
  if (this.timeoutID) {
    window.clearTimeout(this.timeoutID);
    delete this.timeoutID;
  }
  return this;
};