var selectedYear = new Date().getYear(); 
    var monthOptions = null;
    
    function createOption(text, value)
    {
		var option = new Option();
		option.text = text;
		option.value = value;
		return option;
    }
		
    function getMonthOptions()
    {
		if (monthOptions == null)
		{
			monthOptions = new Array();
			monthOptions[monthOptions.length] = createOption("Januari", 0);
			monthOptions[monthOptions.length] = createOption("Februari", 1);
			monthOptions[monthOptions.length] = createOption("Maart", 2);
			monthOptions[monthOptions.length] = createOption("April", 3);
			monthOptions[monthOptions.length] = createOption("Mei", 4);
			monthOptions[monthOptions.length] = createOption("Juni", 5);
			monthOptions[monthOptions.length] = createOption("Juli", 6);
			monthOptions[monthOptions.length] = createOption("Augustus", 7);
			monthOptions[monthOptions.length] = createOption("September", 8);
			monthOptions[monthOptions.length] = createOption("Oktober", 9);
			monthOptions[monthOptions.length] = createOption("November", 10);
			monthOptions[monthOptions.length] = createOption("December", 11);
		}
		return monthOptions;
    }
    
    function loadMonths(monthfield)
    {
		var monthsList = document.getElementById(monthfield.id);
		if (monthsList.options.length == 0)
		{
			var options = getMonthOptions();
			for(var i = 0; i < options.length; i++)
				monthsList.options[i] = options[i];
		} 
    }
    
    function clearOptions(list)
    {
		for(var i = 0; i < list.options.length; i ++)
			list.options[i] = null;
    }
    
    function loadDays(monthfield,dayfield)
    {
		var date = new Date();
		var month = document.getElementById(monthfield.id).value;
		var year = selectedYear;
		
		month ++;
		if (month == 12) // if it was december, move to next year
		{
			month = 0;
			year ++;
		}
		
		// get the next month's first day and substract a day to obtain the last day in the selected month
		date.setFullYear(year, month, 1); 
		date.setDate(0);
		
		var days = date.getDate();
		
		var daysList = document.getElementById(dayfield.id);
		clearOptions(daysList);
		
		for(var i = 1; i <= days; i++)
			daysList.options[i - 1] = new Option(i);
    }
    
    function onYearChanged(yearfield,monthfield,dayfield)
    {		
		
		var textbox = document.getElementById(yearfield.id);
		if (isNaN(textbox.value))
			textbox.value = selectedYear;		
		selectedYear = parseInt(textbox.value);
		textbox.value = selectedYear;
		loadMonths(monthfield);
		loadDays(monthfield,dayfield);
    }
    
    function onMonthChanged(monthfield,dayfield)
    {
		loadDays(monthfield,dayfield);
    }