Archiver = function(format, options) {
  if (!(this instanceof Archiver)) {
    return new Archiver(format, options);
  }

  if (typeof format !== 'string') {
    options = format;
    format = 'zip';
  }

  options = this.options = util.defaults(options, {
    highWaterMark: 1024 * 1024,
    statConcurrency: 4
  });

  Transform.call(this, options);

  this._format = false;
  this._module = false;
  this._pending = 0;
  this._pointer = 0;

  this._entriesCount = 0;
  this._entriesProcessedCount = 0;
  this._fsEntriesTotalBytes = 0;
  this._fsEntriesProcessedBytes = 0;

  this._queue = async.queue(this._onQueueTask.bind(this), 1);
  this._queue.drain = this._onQueueDrain.bind(this);

  this._statQueue = async.queue(this._onStatQueueTask.bind(this), options.statConcurrency);

  this._state = {
    aborted: false,
    finalize: false,
    finalizing: false,
    finalized: false,
    modulePiped: false
  };

  this._streams = [];
}
@constructor
@param {String} format The archive format to use.
@param {(CoreOptions|TransformOptions)} options See also {@link ZipOptions} and {@link TarOptions}.