/**
* 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 it's 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));
        });
    };
})();