var efa_default   = 70;
var efa_increment = 7;

function Efa_Fontsize(increment, def) {

	// check for the W3C DOM
	this.w3c = (document.getElementById);
	
	// check for the MS DOM
	this.ms = (document.all);
	
	// get the userAgent string and normalize case
	this.userAgent = navigator.userAgent.toLowerCase();
	
	// check for Opera and that the version is 7 or higher; note that because of Opera's spoofing we need to
	// resort to some fancy string trickery to extract the version from the userAgent string rather than
	// just using appVersion
	this.isOldOp = ((this.userAgent.indexOf('opera') != -1)&&(parseFloat(this.userAgent.substr(this.userAgent.indexOf('opera')+5)) <= 7));
	
	// check for Mac IE; this has been commented out because there is a simple fix for Mac IE's 'no resizing
	// text in table cells' bug--namely, make sure there is at least one tag (a <p>, <span>, <div>, whatever)
	// containing any content in the table cell; that is, use <td><p>text</p></td> or <th><span>text</span></th>
	// instead of <td>text</td> or <th>text</th>; if you'd prefer not to use the workaround, then uncomment
	// the following line:
	// this.isMacIE = ((this.userAgent.indexOf('msie') != -1) && (this.userAgent.indexOf('mac') != -1) && (this.userAgent.indexOf('opera') == -1));
	
	// check whether the W3C DOM or the MS DOM is present and that the browser isn't Mac IE (if above line is
	// uncommented) or an old version of Opera
	if ((this.w3c || this.ms) && !this.isOldOp && !this.isMacIE) {
		
		// set the name of the function so we can create event handlers later
		this.name = "efa_fontSize";
		
		// set the cookie name to get/save preferences
		this.cookieName = 'efaSize';
		
		// set the increment value to the appropriate parameter
		this.increment = increment;
		
		// default text size as percentage of user default
		this.def = def;
		
		// intended default text size in pixels as a percentage of the assumed 16px
		this.defPx = Math.round(16*(def/100))
		
		// base multiplier to correct for small user defaults
		this.base = 1;
		
		// call the getPrefs function to get preferences saved as a cookie, if any
		this.pref = this.getPref();

		// stuff the HTML for the test <div> into the testHTML property
		this.testHTML = '<div id="efaTest" style="position:absolute; visibility:hidden; line-height:1em;">&nbsp;</div>';

	// set up an onlunload handler to save the user's font size preferences
	} else {
		
		// set the efaInit method to a function that only returns true so
		// we don't get errors in unsupported browsers
		this.efaInit = new Function('return true;');
	}
}

// check the user's current base text size and adjust as necessary
Efa_Fontsize.prototype.efaInit = function() {
	
	// write the test <div> into the document
	document.writeln(this.testHTML);
	
	// get a reference to the body tag
	this.body = (this.w3c) ? document.getElementsByTagName('body')[0].style : document.all.tags('body')[0].style;
	
	// get a reference to the test element
	this.efaTest = (this.w3c) ? document.getElementById('efaTest') : document.all['efaTest'];
	
	// get the height of the test element
	var h = (this.efaTest.clientHeight) ? parseInt(this.efaTest.clientHeight) : (this.efaTest.offsetHeight) ? parseInt(this.efaTest.offsetHeight) : 999;
	
	// check that the current base size is at least as large as the browser default (16px) adjusted
	// by our base percentage; if not, divide 16 by the base size and multiply our base multiplier
	//  by the result to compensate
	if (h < this.defPx) this.base = this.defPx/h;

	// now we set the body font size to the appropriate percentage so the user gets the 
	// font size they selected or our default if they haven't chosen one
	this.body.fontSize = Math.round(this.pref*this.base) + '%';
}

// get the saved preferences out of the cookie, if any
Efa_Fontsize.prototype.getPref = function() {
	
	// get the value of the cookie for this object
	var pref = this.getCookie(this.cookieName);
	
	// if there was a cookie value return it as a number
	if (pref) return parseInt(pref);
	
	// if no cookie value, return the default
	else return this.def;
}

// change the text size; expects a direction parameter of 1 (increase size), -1 (decrease size)
// or 0 (reset to default)
Efa_Fontsize.prototype.setSize = function(direction) {
	
	// see if we were passed a nonzero direction parameter;
	// if so, multiply it by the increment and add it to the current percentage size;
	// if the direction was negative, it will reduce the size; if the direction was positive,
	// it will increase the size; if the direction parameter is undefined or zero, reset
	// current percentage to the default
	this.pref = (direction) ? this.pref + (direction*this.increment) : this.def;
	this.setCookie(this.cookieName,this.pref);
	
	// set the text size
	this.body.fontSize = Math.round(this.pref*this.base) + '%';
}

// get the value of the cookie with the name equal to a string passed as an argument
Efa_Fontsize.prototype.getCookie = function(cookieName) {
	var cookie = cookieManager.getCookie(cookieName);
	return (cookie) ? cookie : false;
}

// set a cookie with a supplied name and value
Efa_Fontsize.prototype.setCookie = function(cookieName,cookieValue) {
	return cookieManager.setCookie(cookieName,cookieValue);
}

var efa_fontSize = new Efa_Fontsize(efa_increment, efa_default);