function $(id){
	return document.getElementById(id);
}
function nao(obj){ // not an object
	if(typeof(obj)=='undefined' || obj==null){
		return true;
	}
	return false;
}

function displayExtras(){
	
	var obj		= null;
	var selObj	= null;
	var reiseart= 'all';
	var i		= 0;

	selObj		= $('reiseart');
	if(nao(selObj)){
		return false;
	}

	reiseart	= selObj.value;
	if(reiseart!='sommer' && reiseart!='winter'){
		showAll();
		return true;
	}
	if(reiseart=='sommer'){
		reiseart	= 'winter';
	}else{
		reiseart	= 'sommer';
	}

	obj		= $('extra['+i+']');
	while(!nao(obj)){
		if( checkExtra(obj.value,reiseart) ){
			obj.parentNode.parentNode.style.display	= 'none';
			obj.disabled							= 'disabled';

		}else if( !checkExtra(obj.value,reiseart)){
			obj.parentNode.parentNode.style.display	= 'block';
			obj.disabled							= '';

		}
		i++;
		obj	= $('extra['+i+']');
	}
	return true;
}

function showAll(){
	var i   = 0;
	var obj = $('extra['+i+']');
	while(!nao(obj)){
		obj.parentNode.parentNode.style.display	= 'block';
		obj.disabled							= '';
		i++;
		obj	= $('extra['+i+']');
	}
}

function checkExtra(extraValue, reiseart){

	var extras	= new Array();
	extras['sommer']	= new Array('warmwasser');
	extras['winter']	= new Array('piste','gletscher','ski','apres');
	
	var c		= extras[reiseart].length;
	var i		= 0;
	for(i=0; i<c; i++){
		if(extraValue==extras[reiseart][i]){
			return true;
		}
	}
	return false;
}

function installDisplayExtras(){

	var obj		= null;
	obj		= $('reiseart');
	if(nao(obj)){
		return false;
	}

	obj.onchange	= displayExtras;
	
	return true;
}