/**
 * createRequestObject()
 * ==================================
 * Creates an XMLHttpRequest object
 * ==================================
 */
function createRequestObject(){
	var request_o;
	var xmlhttp
	/*@cc_on @*/
	/*@if (@_jscript_version >= 5)
	try {
		xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
	}catch(e){
	try {
		xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	} catch (E) {
		xmlhttp=false;
	}
	}
	@else
		xmlhttp=false
	@end @*/
	if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
		try {
			xmlhttp = new XMLHttpRequest();
		} catch (e) {
			xmlhttp=false;
		}
	}
	if (!xmlhttp && window.createRequest) {
		try {
			xmlhttp = window.createRequest();
		} catch (e) {
			xmlhttp=false;
		}
	}
		return xmlhttp;
}
var http;

/**
 * getSuburbs()
 * ==================================
 * Called by a change to the town dropdown
 * Calls the DB to retrieve the list of suburbs for that town
 * ==================================
 */		
function getSuburbs(){
	if(document.searchform.town.selectedIndex){
		// Empties the suburbs dropdown
		document.forms['searchform'].suburb.options.length = 0;
		// Sets the suburbs dropdown to say "Loading"
		document.forms['searchform'].suburb.options[0] = new Option("Loading... ","");
		// Sets index to the selected dropdown option (NOT it's value)
		var index=document.searchform.town.selectedIndex;
		// Retrieves XML from the database with an AJAX call.
		// Sends the VALUE of the selected dropdown index (ie the town id)
		// And a random value to stop caching
		// Initialises a request object
		http = createRequestObject(); 
		http.open('get', 'http://www.funguide.co.nz/ajax_town.php?town='+ document.searchform.town.options[index].value+'&time='+Math.random());
		http.onreadystatechange = handleSuburbs; 
		http.send(null);
	}else{
		// If selectedIndex has no value, the towns dropdown only says "Waiting for region"
		document.forms['searchform'].suburb.options.length = 0;
		document.forms['searchform'].suburb.options[0] = new Option("Waiting for town...","");
	}
}

/**
 * handleSuburbs()
 * ==================================
 * Called by getSuburbs to handle the various states of the AJAX request
 * ==================================
 */		
function handleSuburbs(){
	// If the request has been completed... and we have XML
	if((http.readyState == 4)&&(http.responseXML)){
		// Setup variables
		var XMLResponse = http.responseXML;

		// Get handles to the XML data
		suburb_list = XMLResponse.getElementsByTagName('town').item(0).firstChild.data;
		suburb_id = XMLResponse.getElementsByTagName('suburb');
		
		// Empty the suburb dropdown
		document.forms['searchform'].suburb.options.length = 0;
	
		// Set the first option to "Choose..."
		document.forms['searchform'].suburb.options[0] = new Option("Choose...","");

		// Populate the dropdown
		for(i=0; i<suburb_id.length; i++){
			id =suburb_id[i].getAttribute('id')
			name =suburb_id[i].getElementsByTagName('name').item(0).firstChild.data;
			document.forms['searchform'].suburb.options[i+1] = new Option(name,id);
		}	
	}
	// If the request has been completed... and we have XML
	if((http.readyState == 4)&&(!http.responseXML)){
		document.forms['searchform'].suburb.options[0] = new Option("<No suburbs available>","");
	}
}