/*

Copyright (c) 2009, Yahoo! Inc. All rights reserved.

Code licensed under the BSD License:

http://developer.yahoo.net/yui/license.txt

version: 3.0.0b1

build: 1163

*/

YUI.add('io-queue', function(Y) {

   /**

    * Extends the IO base class to implement Queue for synchronous

    * transaction processing.

	* @module io

	* @submodule io-queue

	*/

   /**

	* @description Array of transactions queued for processing

	*

	* @property _yQ

	* @private

	* @static

	* @type Object

	*/

	var _q = new Y.Queue(),

   /**

	* @description Reference to "io:complete" event handler.

	*

	* @property _e

	* @private

	* @static

	* @type Object

	*/

	_e,

	_activeId,

   /**

	* @description Property to determine whether the queue is set to

	* 1 (active) or 0 (inactive).  When inactive, transactions

	* will be stored in the queue until the queue is set to active.

	*

	* @property _qState

	* @private

	* @static

	* @type int

	*/

	_qState = 1;

   /**

	* @description Method for requesting a transaction, and queueing the

	* request before it is sent to the resource.

	*

	* @method _queue

	* @private

	* @static

	* @return Object

	*/

	function _queue(uri, c) {

		var o = { uri: uri, id: Y.io._id(), cfg:c };

		_q.add(o);

		if (_qState === 1) {

			_shift();

		}

		Y.log('Object queued.  Transaction id is' + o.id, 'info', 'io');

		return o;

	}

   /**

	* @description Method Process the first transaction from the

	* queue in FIFO order.

	*

	* @method _shift

	* @private

	* @static

	* @return void

	*/

	function _shift() {

		var o = _q.next();

		_activeId = o.id;

		_qState = 0;

		Y.io(o.uri, o.cfg, o.id);

	}

   /**

	* @description Method for promoting a transaction to the top of the queue.

	*

	* @method _unshift

	* @private

	* @static

	* @return void

	*/

	function _unshift(o) {

		_q.promote(o);

	}

	function _next(id) {

		_qState = 1;

		if (_activeId === id && _q.size() > 0) {

			_shift();

		}

	}

   /**

	* @description Method for removing a specific, pending transaction from

	* the queue.

	*

	* @method _remove

	* @private

	* @static

	* @return void

	*/

	function _remove(o) {

		_q.remove(o);

	}

	function _start() {

		_qState = 1;

		if (_q.size() > 0) {

			_shift();

		}

		Y.log('Queue started.', 'info', 'io');

	}

   /**

	* @description Method for setting queue processing to inactive.

	* Transaction requests to YUI.io.queue() will be stored in the queue, but

	* not processed until the queue is reset to "active".

	*

	* @method _stop

	* @private

	* @static

	* @return void

	*/

	function _stop() {

		_qState = 0;

		Y.log('Queue stopped.', 'info', 'io');

	};

   /**

	* @description Method to query the current size of the queue.

	*

	* @method _size

	* @private

	* @static

	* @return int

	*/

	function _size() {

		return _q.size();

	};

	_e = Y.on('io:complete', function(id) { _next(id); }, Y.io);

   /**

	* @description Method to query the current size of the queue, or to

	* set a maximum queue size.  This is the interface for _size().

	*

	* @method size

	* @public

	* @static

	* @param {number} i - Specified maximum size of queue.

    * @return number

	*/

	_queue.size = _size;

   /**

	* @description Method for setting the queue to active. If there are

	* transactions pending in the queue, they will be processed from the

	* queue in FIFO order. This is the interface for _start().

	*

	* @method start

	* @public

	* @static

    * @return void

	*/

	_queue.start = _start;

   /**

	* @description Method for setting queue processing to inactive.

	* Transaction requests to YUI.io.queue() will be stored in the queue, but

	* not processed until the queue is restarted. This is the

	* interface for _stop().

	*

	* @method stop

	* @public

	* @static

    * @return void

	*/

	_queue.stop = _stop;

   /**

	* @description Method for promoting a transaction to the top of the queue.

	* This is the interface for _unshift().

	*

	* @method promote

	* @public

	* @static

	* @param {Object} o - Reference to queued transaction.

    * @return void

	*/

	_queue.promote = _unshift;

   /**

	* @description Method for removing a specific, pending transaction from

	* the queue. This is the interface for _purge().

	*

	* @method purge

	* @public

	* @static

	* @param {Object} o - Reference to queued transaction.

    * @return void

	*/

	_queue.remove = _remove;

    Y.mix(Y.io, {

		queue: _queue

    }, true);

}, '3.0.0b1' ,{requires:['io-base']});