/* Page Font Size Control (PFSC) Javascript */
/* Copyright (C) 2010 Skye Nott, F4 Systems */

/* This depends on site CSS specifying font-size using em ONLY, i
 * with a font-size in % in the body {}. Typically, one can use the
 * "body { font-size: 62.5%; }" pattern so that 1.0em = 10px
 */

var PFSC = function () {

/* Private configuration variables. */
var MIN_PCT 		= 50;
var MAX_PCT 		= 100;
var DEFAULT_PCT 	= 62.5;
var STEP_PCT 		= 0.03;
var DEBUG 		= false;
var COOKIE_NAME 	= "pfsc_pct";
var SAVE_ELEM_ID 	= "pfsc_save";
var SAVE_OK_FG 		= '#fff';
var SAVE_OK_BG 		= '#0f0';
var SAVE_FAIL_FG 	= '#fff';
var SAVE_FAIL_BG 	= '#f00';


/* Private functions */

var getFontSize = function () {
	if (document.body.style.fontSize == "")
		return setFontSize(DEFAULT_PCT);
	return parseFloat(document.body.style.fontSize);
};

var setFontSize = function(sizepct) {
	document.body.style.fontSize = sizepct + "%";
	debugMessage("Set body size to " + sizepct + "%");
	return sizepct;
};

var loadCookie = function() {
	if (document.cookie.length < 1)
		return 0;
	c_start = document.cookie.indexOf(COOKIE_NAME + "=");
	if (c_start == -1)
		return 0;
	c_start = c_start + COOKIE_NAME.length + 1;
	c_end = document.cookie.indexOf(";", c_start);
	if (c_end==-1) c_end=document.cookie.length;
	value = unescape(document.cookie.substring(c_start,c_end));
	debugMessage("Get cookie " + COOKIE_NAME + " " + value + "%");
	return parseFloat(value);
};

var setCookie = function(value) {
	var exdate = new Date();
	exdate.setDate(exdate.getDate() + 256); /* days */
	document.cookie = COOKIE_NAME + "=" + escape(value) + ";expires=" + exdate.toUTCString() + ";path=/";
	debugMessage("Set cookie " + COOKIE_NAME + " to " + value + "%");
	return true;
};

var addLoadEvent = function(func) {
	var oldonload = window.onload;
	if (typeof window.onload != "function")
		window.onload = func;
	else {
		window.onload = function() {
			func();
			oldonload();
		}
	}
};

var debugMessage = function(str) {
	if (DEBUG)
	    window.status = "PFSC: " + str;
};

var restoreAttributes = function(elem, fg, bg) {
	//alert("restoreAttributes fired!\nfg=" + fg + " bg=" + bg);
	if (!elem) return;
	elem.style.color = fg;
	elem.style.background = bg;
};

/* http://robertnyman.com/2006/04/24/get-the-rendered-style-of-an-element/ */
var getStyle = function(oElm, strCssRule) {
	var strValue = "";
	if (document.defaultView && document.defaultView.getComputedStyle) {
		strValue = document.defaultView.getComputedStyle(oElm, "").getPropertyValue(strCssRule);
	} else if (oElm.currentStyle) {
		strCssRule = strCssRule.replace(/\-(\w)/g, function (strMatch, p1) {
			return p1.toUpperCase();
		});
		strValue = oElm.currentStyle[strCssRule];
	}
	return strValue;
}

/* Construct public interface object */
return {
	init: function () {
		// No longer needed; page.php reads cookie and puts in HTML HEAD CSS.
		//addLoadEvent(this.loadFontSize);
	},
	
	increaseFontSize: function () {
		var newsize = getFontSize() * (1 + STEP_PCT);
		var rounded = Math.round(newsize * 100) / 100;
		setFontSize(Math.min(rounded, MAX_PCT));
		return true;
	},
	
	decreaseFontSize: function() {
		var newsize = getFontSize() * (1 - STEP_PCT);
		var rounded = Math.round(newsize * 100) / 100;
		setFontSize(Math.max(rounded, MIN_PCT));
		return true;
	},
	
	resetFontSize: function() {
		setFontSize(DEFAULT_PCT);
		return this.saveFontSize();
	},
	
	loadFontSize: function() {
		sizepct = loadCookie();
		if (sizepct) {
		    if (sizepct < MIN_PCT) { sizepct = MIN_PCT; }
		    if (sizepct > MAX_PCT) { sizepct = MAX_PCT; }
		    setFontSize(sizepct);
		} else {
		    sizepct = getFontSize();
		}
		debugMessage("Loaded " + sizepct + "%");
		return true;	
	},
	
	saveFontSize: function() {
		var sizepct = getFontSize();
		if (setCookie(sizepct)) {
			var elem = document.getElementById(SAVE_ELEM_ID);
			if (elem) {
				var oldfg = getStyle(elem, "color");
				var oldbg = getStyle(elem, "background");
				if (!oldfg) oldfg = 'inherit';
				if (!oldbg) oldbg = 'inherit';
				elem.style.color = SAVE_OK_FG;
				elem.style.background = SAVE_OK_BG;
				window.setTimeout(function(){ restoreAttributes(elem, oldfg, oldbg) }, 1500);
			}
		}
		debugMessage("Saved " + sizepct + "%");
		return true;	
	}
};

}();

PFSC.init();