/** 
 *  @fileoverview TextResizeDetector
 * 
 *  Detects changes to font sizes when user changes browser settings
 *  <br>Fires a custom event with the following data:<br><br>
 * 	iBase  : base font size  	
 *	iDelta : difference in pixels from previous setting<br>
 *  	iSize  : size in pixel of text<br>
 *  
 *  * @author Lawrence Carvalho carvalho@uk.yahoo-inc.com
 * @version 1.0
 */

/**
 * @constructor
 */
TextResizeDetector = function() {
	var el = null;
	var iIntervalDelay = 200;
	var iInterval = null;
	var iCurrSize = -1;
	var iBase = -1;
	var aListeners = [];
	var createControlElement = function() {
		el = document.createElement('span');
		el.id = 'textResizeControl';
		el.innerHTML = '&nbsp;';
		el.style.position = "absolute";
		el.style.left = "-9999px";
		var elC = document.getElementById(TextResizeDetector.TARGET_ELEMENT_ID);
		// insert before firstChild
		if (elC)
			elC.insertBefore(el, elC.firstChild);
		iBase = iCurrSize = TextResizeDetector.getSize();
	};

	function _stopDetector() {
		window.clearInterval(iInterval);
		iInterval = null;
	}
	;
	function _startDetector() {
		if (!iInterval) {
			iInterval = window.setInterval('TextResizeDetector.detect()',
					iIntervalDelay);
		}
	}
	;

	function _detect() {
		var iNewSize = TextResizeDetector.getSize();

		if (iNewSize !== iCurrSize) {
			for ( var i = 0; i < aListeners.length; i++) {
				aListnr = aListeners[i];
				var oArgs = {
					iBase : iBase,
					iDelta : ((iCurrSize != -1) ? iNewSize - iCurrSize + 'px'
							: "0px"),
					iSize : iCurrSize = iNewSize
				};
				if (!aListnr.obj) {
					aListnr.fn('textSizeChanged', [ oArgs ]);
				} else {
					aListnr.fn.apply(aListnr.obj, [ 'textSizeChanged',
							[ oArgs ] ]);
				}
			}

		}
		return iCurrSize;
	}
	;
	var onAvailable = function() {

		if (!TextResizeDetector.onAvailableCount_i) {
			TextResizeDetector.onAvailableCount_i = 0;
		}

		if (document.getElementById(TextResizeDetector.TARGET_ELEMENT_ID)) {
			TextResizeDetector.init();
			if (TextResizeDetector.USER_INIT_FUNC) {
				TextResizeDetector.USER_INIT_FUNC();
			}
			TextResizeDetector.onAvailableCount_i = null;
		} else {
			if (TextResizeDetector.onAvailableCount_i < 600) {
				TextResizeDetector.onAvailableCount_i++;
				setTimeout(onAvailable, 200)
			}
		}
	};
	setTimeout(onAvailable, 500);

	return {
		/*
		 * Initializes the detector
		 * 
		 * @param {String} sId The id of the element in which to create the
		 * control element
		 */
		init : function() {

			createControlElement();
			_startDetector();
		},
		/**
		 * Adds listeners to the ontextsizechange event. Returns the base font
		 * size
		 * 
		 */
		addEventListener : function(fn, obj, bScope) {
			aListeners[aListeners.length] = {
				fn : fn,
				obj : obj
			}
			return iBase;
		},
		/**
		 * performs the detection and fires textSizeChanged event
		 * 
		 * @return the current font size
		 * @type {integer}
		 */
		detect : function() {
			return _detect();
		},
		/**
		 * Returns the height of the control element
		 * 
		 * @return the current height of control element
		 * @type {integer}
		 */
		getSize : function() {
			var iSize;
			return el.offsetHeight;

		},
		/**
		 * Stops the detector
		 */
		stopDetector : function() {
			return _stopDetector();
		},
		/*
		 * Starts the detector
		 */
		startDetector : function() {
			return _startDetector();
		}
	}
}();

TextResizeDetector.TARGET_ELEMENT_ID = 'doc';
TextResizeDetector.USER_INIT_FUNC = null;