function clean_content(elementID){
		document.getElementById(elementID).innerHTML='';
}

function login(phpfile,username,password){
	clean_content('loginfail');
	login_send_http_req(phpfile+'?action=validate&username='+username+"&password="+password,document.getElementById('loginform'));
	return true;
}

function logout(phpfile){
	login_send_http_req(phpfile+'?action=logout',document.getElementById('loginsuc'));
	return true;
}

function login_send_http_req(url, target_element) {

	var http = (window.XMLHttpRequest) ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");

	if (!http) return false;

	http.open('get', url);

	http.onreadystatechange = function () { 

		if(http.readyState!=4) return;
		if(http.responseText.isEmpty()) return;
		
		var targetID = target_element ? target_element.getAttribute('id') : null;
		
		if(targetID=='loginform'){ // result from login
			var succeed = http.responseText.getTagValue('bool')=='suc';
			var result  = http.responseText.getTagValue('result');		
			if(succeed){
				target_element.style.display='none';
				document.getElementById('loginsuc').style.display='block';
				document.getElementById('loginusername').innerHTML = result;
			}else{
				document.getElementById('loginfail').innerHTML=result;
			}
		}
		else if(targetID=='loginsuc'){ // result from logout
			var succeed = http.responseText.getTagValue('bool')=='suc';;
			if(succeed){
				document.getElementById('loginusername').innerHTML='';
				target_element.style.display='none';
				document.getElementById('loginform').style.display='block';
			} else{
				alert(http.responseText);
			}
		}
		else{ alert(http.responseText); }
	};
	http.send('');
}