/*
 * jQuery Extra Selectors - (c) Keith Clark freely distributable under the terms of the MIT license.
 * 
 * twitter.com/keithclarkcouk
 * www.keithclark.co.uk
 */

(function($) {
	function getNthIndex(cur, dir) {
		var t = cur, idx = 0;
		while (cur = cur[dir] ) {
			if (t.tagName == cur.tagName) {
				idx++;
			}
		}
		return idx;
	}

	function isNthOf(elm, pattern, dir) {
		var position = getNthIndex(elm, dir), loop;
		if (pattern == "odd" || pattern == "even") {
			loop = 2;
			position -= !(pattern == "odd");
		} else {
			var nth = pattern.indexOf("n");
			if (nth > -1) {
				loop = parseInt(pattern, 10) || parseInt(pattern.substring(0, nth) + "1", 10);
				position -= (parseInt(pattern.substring(nth + 1), 10) || 0) - 1;
			} else {
				loop = position + 1;
				position -= parseInt(pattern, 10) - 1;
			}
		}
		return (loop<0 ? position<=0 : position >= 0) && position % loop == 0
	}

	var pseudos = {
		"first-of-type": function(elm) {
			return getNthIndex(elm, "previousSibling") == 0;
		},
		"last-of-type": function(elm) { 
			return getNthIndex(elm, "nextSibling") == 0;
		},
		"only-of-type": function(elm) { 
			return pseudos["first-of-type"](elm) && pseudos["last-of-type"](elm);
		},
		"nth-of-type": function(elm, i, match) {
			return isNthOf(elm, match[3], "previousSibling");
		},
		"nth-last-of-type": function(elm, i, match) {
			return isNthOf(elm, match[3], "nextSibling");
		}		
	}
	$.extend($.expr[':'], pseudos);
}(jQuery));