function dt_days(month, year){
    if (month==4 || month==6 || month==9 || month==11){
        return 30;
    } else if(month == 2) {
        if(year % 4 == 0){
            return 29;
        } else {
            return 28;
        }
    } else {
        return 31;
    }
}

function dt_options(month, year, selectedIndex){
    var options = new Array();
    var daysCount = dt_days(month, year);
    var newSelectedIndex;

    if(daysCount<selectedIndex+1){
        newSelectedIndex = daysCount -1;
    } else {
        newSelectedIndex = selectedIndex;
    }

    for(i=0; i<daysCount; i++)
        options[i] = new Option(i+1, i+1, false, false);

    options[newSelectedIndex].selected = true;

    return options;
}

function dt_setDay(dayId, monthId, yearId){
	daySelect = document.getElementById(dayId);
	monthSelect = document.getElementById(monthId);
	yearSelect = document.getElementById(yearId);

	if(daySelect == null || monthSelect == null || yearSelect ==null) return;

	month = monthSelect.options[monthSelect.selectedIndex].value;
	year = yearSelect.options[yearSelect.selectedIndex].value;
	selectedIndex = daySelect.selectedIndex;
	if(selectedIndex == -1) selectedIndex = 0;

	newOptions = dt_options(month, year, selectedIndex);

	for(i=0; i< newOptions.length; i++){
		daySelect.options[i]=newOptions[i];
	}
	oldLength = daySelect.options.length;
	for(i=newOptions.length; i<oldLength; i++){
		daySelect.options[newOptions.length]=null;
	}
}

function dt_getDateString(yearId,monthId,dayId) {
	d_obj= document.getElementById(dayId);
	m_obj= document.getElementById(monthId);
	y_obj= document.getElementById(yearId);
	var y = y_obj.options[y_obj.selectedIndex].value;
	var m = m_obj.options[m_obj.selectedIndex].value;
	var d = d_obj.options[d_obj.selectedIndex].value;
	if (y=="" || m=="") { return null; }
	if (d=="") { d=1; }
	return str= y+'-'+m+'-'+d;
}