var a_optionsCashe = [],
	o_request;

function f_updateOptions (e_source) {

	var s_source = e_source.name;
	var e_form = e_source.form;
	var s_value = e_source.options[e_source.options.selectedIndex].value;
	var a_values = s_value.split('|');
	var n_parentID = a_values[0];
	var s_link =  a_values[1];
	var s_target =  a_values[2];
	
	// open URL if supplied
	if (s_link) {
			window.open(s_link, '_blank');
	}
	
	// reset and disalbe dependent selects if option doesn't have sub-options
	if (!n_parentID) {
		var b_under = false;
		for (var i = 0; i < a_hierarchy.length; i++) {
			if (b_under) {
				e_form[a_hierarchy[i]].options.length = 1;
				e_form[a_hierarchy[i]].disabled = true;
			}
			else if (a_hierarchy[i] == s_source)
				b_under = true;
		}
		return;
	}
	
	// determine direcly dependent select
	var s_target;
	for (var i = 0; i < a_hierarchy.length; i++)
		if (a_hierarchy[i] == s_source) {
			s_target = a_hierarchy[i + 1]
			break;
		}
	var e_target = e_form.elements[s_target];
	if (!e_target) return;
	
	// use cached values if available
	if (a_optionsCashe[n_parentID]) {
		f_populateOptions(e_target, a_optionsCashe[n_parentID]);
		return;
	}

	// submit new ajax request for options
	window.o_request = {
		'target': e_target,
		'source': e_source,
		'parent_id' : n_parentID
	};
	if (window.ActiveXObject) 
		o_request.o_http = new ActiveXObject("Microsoft.XMLHTTP");
	else if (window.XMLHttpRequest) 
		o_request.o_http = new XMLHttpRequest();
	else
		throw 'AJAX is not supported';

	e_source.disabled = true;
	o_request.o_http.onreadystatechange = f_processRequest;
	o_request.o_http.open("GET", 'asbackend.php?id=' + n_parentID, true);
	o_request.o_http.send(null);
}

function f_populateOptions (e_target, a_options) {

	if (!e_target)
		return;
	e_target.options.length = 1;
	for (var i = 0; i < a_options.length; i++)
		e_target.options[e_target.options.length] = new Option (
			a_options[i]['text'] + (a_options[i]['children'] ? ' (' + a_options[i]['children'] + ')' : ''),
			(a_options[i]['id'] ? a_options[i]['id'] : '') + '|' +
			(a_options[i]['link'] ? a_options[i]['link'] : '') +
			(a_options[i]['target'] ? '|' + a_options[i]['target'] : '')
		);

	e_target.disabled = false;
	e_target.focus();
}

function f_processRequest () {

	if (!window.o_request || o_request.o_http.readyState != 4)
		return;

	o_request['source'].disabled = false;
	if (o_request.o_http.status != 200 && o_request.o_http.status != 304)
		throw 'AJAX response error';

	// parse XML
	var e_xml = o_request.o_http.responseXML;
	var o_options = e_xml.getElementsByTagName('option');
	var a_options = [],
		o_option, s_id, s_link, s_target;

	for (var i = 0; i < o_options.length; i++) {
		o_option = o_options[i];
		var a_option = {
			'text': o_option.firstChild.nodeValue,
			'id' : o_option.getAttribute('id'),
			'children' : o_option.getAttribute('children'),
			'link' : o_option.getAttribute('href'),
			'target': o_option.getAttribute('target')
		};
		a_options[a_options.length] = a_option;
	}

	// add to cache and update the selectbox
	a_optionsCashe[o_request['parent_id']] = a_options;
	f_populateOptions(o_request['target'], a_options);
}