/**
* @projectDescription Monitor Font Size Changes with jQuery
*
* @version 1.0
* @author Dave Cardwell
*
* jQuery-Em - $Revision: 24 $ ($Date: 2007-08-19 11:24:56 +0100 (Sun, 19 Aug 2007) $)
* http://davecardwell.co.uk/javascript/jquery/plugins/jquery-em/
*
* Copyright ©2007 Dave Cardwell <http://davecardwell.co.uk/>
*
* Released under the MIT licence:
* http://www.opensource.org/licenses/mit-license.php
*/

// Upon $(document).ready()…
jQuery(function($) {
	// Configuration…
	var eventName = 'emchange';


	// Set up default options.
	$.em = $.extend({
		/**
		* The jQuery-Em version string.
		*
		* @example $.em.version;
		* @desc '1.0a'
		*
		* @property
		* @name version
		* @type String
		* @cat Plugins/Em
		*/
		version: '1.0',

		/**
		* The number of milliseconds to wait when polling for changes to the
		* font size.
		*
		* @example $.em.delay = 400;
		* @desc Defaults to 200.
		*
		* @property
		* @name delay
		* @type Number
		* @cat Plugins/Em
		*/
		delay: 200,

		/**
		* The element used to detect changes to the font size.
		*
		* @example $.em.element = $('<div />')[0];
		* @desc Default is an empty, absolutely positioned, 100em-wide <div>.
		*
		* @private
		* @property
		* @name element
		* @type Element
		* @cat Plugins/Em
		*/
		element: $('<div />').css({ left: '-100em',
			position: 'absolute',
			width: '100em'
		})
                             .prependTo('body')[0],

		/**
		* The action to perform when a change in the font size is detected.
		*
		* @example $.em.action = function() { ... }
		* @desc The default action is to trigger a global “emchange” event.
		* You probably shouldn’t change this behaviour as other plugins may
		* rely on it, but the option is here for completion.
		*
		* @example $(document).bind('emchange', function(e, cur, prev) {...})
		* @desc Any functions triggered on this event are passed the current
		* font size, and last known font size as additional parameters.
		*
		* @private
		* @property
		* @name action
		* @type Function
		* @cat Plugins/Em
		* @see current
		* @see previous
		*/
		action: function() {
			var currentWidth = $.em.element.offsetWidth / 100;

			// If the font size has changed since we last checked…
			if (currentWidth != $.em.current) {
				/**
				* The previous pixel value of the user agent’s font size. See
				* $.em.current for caveats. Will initially be undefined until
				* the “emchange” event is triggered.
				*
				* @example $.em.previous;
				* @result 16
				*
				* @property
				* @name previous
				* @type Number
				* @cat Plugins/Em
				* @see current
				*/
				$.em.previous = $.em.current;

				/**
				* The current pixel value of the user agent’s font size. As
				* with $.em.previous, this value *may* be subject to minor
				* browser rounding errors that mean you might not want to
				* rely upon it as an absolute value.
				*
				* @example $.em.current;
				* @result 14
				*
				* @property
				* @name current
				* @type Number
				* @cat Plugins/Em
				* @see previous
				*/
				$.em.current = currentWidth;

				$.event.trigger(eventName, [$.em.current, $.em.previous]);
			}
		}
	}, $.em);


	/**
	* Bind a function to the emchange event of each matched element.
	*
	* @example $("p").emchange( function() { alert("Hello"); } );
	*
	* @name emchange
	* @type jQuery
	* @param Function fn A function to bind to the emchange event.
	* @cat Plugins/Em
	*/

	/**
	* Trigger the emchange event of each matched element.
	*
	* @example $("p").emchange()
	*
	* @name emchange
	* @type jQuery
	* @cat Plugins/Em
	*/
	$.fn[eventName] = function(fn) {
		return fn ? this.bind(eventName, fn)
                                               : this.trigger(eventName);
	};


	// Store the initial pixel value of the user agent’s font size.
	$.em.current = $.em.element.offsetWidth / 100;

	/**
	* While polling for font-size changes, $.em.iid stores the intervalID in
	* case you should want to cancel with clearInterval().
	*
	* @example window.clearInterval( $.em.iid );
	* 
	* @property
	* @name iid
	* @type Number
	* @cat Plugins/Em
	*/
	$.em.iid = setInterval($.em.action, $.em.delay);
});