/**
 * jQuery.fn.sortElements
 * --------------
 * @param Function comparator:
 *   Exactly the same behaviour as [1,2,3].sort(comparator)
 *
 * @param Function getSortable
 *   A function that should return the element that is
 *   to be sorted. The comparator will run on the
 *   current collection, but you may want the actual
 *   resulting sort to occur on a parent or another
 *   associated element.
 *
 *   E.g. $('td').sortElements(comparator, function(){
 *      return this.parentNode;
 *   })
 *
 *   The <td>'s parent (<tr>) will be sorted instead
 *   of the <td> itself.
 */
jQuery.fn.sortElements = (function() {

	var sort = [].sort;

	return function(comparator, getSortable) {
		getSortable = getSortable ||
		function() {
			return this;
		};

		var placements = this.map(function() {

			var sortElement = getSortable.call(this), parentNode = sortElement.parentNode,

			// Since the element itself will change position, we have
			// to have some way of storing its original position in
			// the DOM. The easiest way is to have a 'flag' node:
			nextSibling = parentNode.insertBefore(document.createTextNode(''), sortElement.nextSibling);

			return function() {

				if(parentNode === this) {
					throw new Error("You can't sort elements if any one is a descendant of another.");
				}

				// Insert before flag:
				parentNode.insertBefore(this, nextSibling);
				// Remove flag:
				parentNode.removeChild(nextSibling);

			};
		});
		return sort.call(this, comparator).each(function(i) {
			placements[i].call(getSortable.call(this));
		});
	};
})();