ObjectSetPrototypeOf(Duplex.prototype, Readable.prototype);
ObjectSetPrototypeOf(Duplex, Readable);

{
  const keys = ObjectKeys(Writable.prototype);
  // Allow the keys array to be GC'ed.
  for (let i = 0; i < keys.length; i++) {
    const method = keys[i];
    if (!Duplex.prototype[method])
      Duplex.prototype[method] = Writable.prototype[method];
  }
}

function Duplex(options) {
  if (!(this instanceof Duplex))
    return new Duplex(options);

  Readable.call(this, options);
  Writable.call(this, options);

  if (options) {
    this.allowHalfOpen = options.allowHalfOpen !== false;

    if (options.readable === false) {
      this._readableState.readable = false;
      this._readableState.ended = true;
      this._readableState.endEmitted = true;
    }

    if (options.writable === false) {
      this._writableState.writable = false;
      this._writableState.ending = true;
      this._writableState.ended = true;
      this._writableState.finished = true;
    }
  } else {
    this.allowHalfOpen = true;
  }
}

ObjectDefineProperties(Duplex.prototype, {
  writable:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writable') },
  writableHighWaterMark:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableHighWaterMark') },
  writableObjectMode:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableObjectMode') },
  writableBuffer:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableBuffer') },
  writableLength:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableLength') },
  writableFinished:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableFinished') },
  writableCorked:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableCorked') },
  writableEnded:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableEnded') },
  writableNeedDrain:
    { __proto__: null, ...ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableNeedDrain') },

  destroyed: {
    __proto__: null,
    get() {
      if (this._readableState === undefined ||
        this._writableState === undefined) {
        return false;
      }
      return this._readableState.destroyed && this._writableState.destroyed;
    },
    set(value) {
      // Backward compatibility, the user is explicitly
      // managing destroyed.
      if (this._readableState && this._writableState) {
        this._readableState.destroyed = value;
        this._writableState.destroyed = value;
      }
    },
  },
});

let webStreamsAdapters;

// Lazy to avoid circular references
function lazyWebStreams() {
  if (webStreamsAdapters === undefined)
    webStreamsAdapters = require('internal/webstreams/adapters');
  return webStreamsAdapters;
}

Duplex.fromWeb = function(pair, options) {
  return lazyWebStreams().newStreamDuplexFromReadableWritablePair(
    pair,
    options);
};

Duplex.toWeb = function(duplex) {
  return lazyWebStreams().newReadableWritablePairFromDuplex(duplex);
};

let duplexify;

Duplex.from = function(body) {
  if (!duplexify) {
    duplexify = require('internal/streams/duplexify');
  }
  return duplexify(body, 'body');
};