// fill in Year options	
function fillElementYear() {
	var element = this.elementYear;
	element.options[0] = new Option("1999", "1999");
	element.options[1] = new Option("2000", "2000");
	element.options[2] = new Option("2001", "2001");
	element.options[3] = new Option("2002", "2002");
	element.options[this.date.getFullYear() - 1999].selected=true;
}

// fill in Month options
function fillElementMonth() {
	var element = this.elementMonth;
	var months = new Array("January","February","March","April","May","June",
                  "July","August","September","October","November","December");
	for (i = 0; i < 12; i++) {
		element.options[i] = new Option(months[i], i + 1);
	}
	element.options[this.date.getMonth()].selected=true;
}

// fill in Day options
function fillElementDay() {
	var element = this.elementDay;
	var days = this.getMaxDays(this.date.getMonth(), this.date.getYear());
	
	if (this.date.getDate() > days) {
		this.date.setDate(days);
	}
	
	// add days
	if (element.length < days) {
		for (i = element.length; i < days; i++) {
			element.options[i] = new Option(i+1, i+1);
		}
	}
	// subtrack days
	else if (element.length > days) {
		for (i = element.length; i >= days; i--) {
			element.options[i] = null;
		}
	}
	
	element.options[this.date.getDate()-1].selected=true;
}

// returns the last day(number) in month or maximium day
function getMaxDays(month, year) {
	month++;

	var maxDays=31;//default

	// months with 30 days
	if (month==4 || month==6 || month==9 || month==11) {
		maxDays=30
	}

	// february, leap year
	if (month==2) {
		// feb
		if ((year/4)!=parseInt(year/4)) {
			maxDays=28
		}
		else {
			//leap year
			maxDays=29
		}
	}
	return maxDays
}



function fillElements() {
	this.fillElementYear();
	this.fillElementMonth();
	this.fillElementDay();
}

function update(field) {
	switch (field) {
	case "Year" :
		this.date.setFullYear(this.elementYear[this.elementYear.selectedIndex].value);
		break;
		
	case "Month" :
		var month = this.elementMonth[this.elementMonth.selectedIndex].value - 1;
		var maxDays = this.getMaxDays(month, this.date.getYear());
		if (this.date.getDate() > maxDays) { 
			this.date.setDate(maxDays);
		}
		this.date.setMonth(month);
		break;
		
	case "Day" :  
		this.date.setDate(this.elementDay[this.elementDay.selectedIndex].value);
		break;
		
	}
	this.fillElementDay();
}

// create FormDate Object
function FormDate(date, form, elementNameYear, elementNameMonth, elementNameDay) {
	// fields
	this.date = date;
	this.form = form;
	this.elementYear = form.elements[elementNameYear];
	this.elementMonth = form.elements[elementNameMonth];
	this.elementDay = form.elements[elementNameDay];
	
	// methods
	this.getMaxDays = getMaxDays;
	this.fillElementYear = fillElementYear;
	this.fillElementMonth = fillElementMonth;	
	this.fillElementDay = fillElementDay;
	this.fillElements = fillElements;
	this.update = update;
}