/*

Switching Styles
----------------

First we need the script to be able to differentiate between the three different types of style sheet. This is relatively easy to do, as we only need to check two of the attributes of each link element.

Is it a link to a style sheet?

HTMLLinkElement.getAttribute("rel").indexOf("style") != -1

Is there a title attribute?

HTMLListElement.getAttribute("title")

Does the rel attribute contain the keyword "alternate"?

HTMLLinkElement.getAttribute("rel").indexOf("alt") != -1

Note that we check for the string ÒaltÓ because some browsers accept the keyword ÒalternativeÓ in place of Òalternate.Ó

Using these three checks we can write a function to switch style sheets. This involves looping through every link element in the document, disabling all preferred and alternate style sheets that we donÕt want active, and enabling all preferred and alternate style sheets that we do want active.

Note that only preferred and alternate style sheet link elements will have a title attribute.


Cookies
-------

Now we can change the style sheet. Cool. We have a more personalized page. Excellent. But we donÕt have a personalized site. The preference is only applied to the current page; when we leave the current page the preference leaves with us. This situation, however, can be rectified with a cookie.

To store a cookie we need another function to return the current style sheet. We also need two functions to store and read the cookie.

To return the current style sheet we look for an active preferred or alternate style sheet and check its title.

First we loop through all the link elements in the document again. We then check whether the link is a style sheet. If it is, we check whether the style sheet has a title. This tells us that the style sheet is either preferred or alternative.

The last check is to see whether or not the style sheet is active. If all three checks return true, we have the current style sheet and we can return the title.

For implementation details and cookie functions see http://www.alistapart.com/articles/alternate/

*/


	function setActiveStyleSheet(title) {
	  var i, a, main;
	  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
	    if(a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title")) {
	      a.disabled = true;
	      if(a.getAttribute("title") == title) a.disabled = false;
	    }
	  }
	}
	
	function getActiveStyleSheet() {
	  var i, a;
	  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
	    if(a.getAttribute("rel").indexOf("style") != -1 && a.getAttribute("title") && !a.disabled) return a.getAttribute("title");
	  }
	  return null;
	}
	
	function getPreferredStyleSheet() {
	  var i, a;
	  for(i=0; (a = document.getElementsByTagName("link")[i]); i++) {
	    if(a.getAttribute("rel").indexOf("style") != -1
	       && a.getAttribute("rel").indexOf("alt") == -1
	       && a.getAttribute("title")
	       ) return a.getAttribute("title");
	  }
	  return null;
	}
	
	function createCookie(name,value,days) {
	  if (days) {
	    var date = new Date();
	    date.setTime(date.getTime()+(days*24*60*60*1000));
	    var expires = "; expires="+date.toGMTString();
	  }
	  else expires = "";
	  document.cookie = name+"="+value+expires+"; path=/";
	}
	
	function readCookie(name) {
	  var nameEQ = name + "=";
	  var ca = document.cookie.split(';');
	  for(var i=0;i < ca.length;i++) {
	    var c = ca[i];
	    while (c.charAt(0)==' ') c = c.substring(1,c.length);
	    if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
	  }
	  return null;
	}
	
	window.onload = function(e) {
	  var cookie = readCookie("style");
	  var title = cookie ? cookie : getPreferredStyleSheet();
	  setActiveStyleSheet(title);
	}
	
	window.onunload = function(e) {
	  var title = getActiveStyleSheet();
	  createCookie("style", title, 365);
	}
	
	var cookie = readCookie("style");
	var title = cookie ? cookie : getPreferredStyleSheet();
	setActiveStyleSheet(title);