var daysInMonth = [31,29,31,30,31,30,31,31,30,31,30,31];
var monthes = ['Январь','Февраль','Март','Апрель','Май','Июнь','Июль','Август','Сентябрь','Октябрь','Ноябрь','Декабрь'];

function initForm() {
	switchFormState();
	fillYears(document.getElementById('user_begin_year'),user_begin_year);
	fillYears(document.getElementById('user_end_year'),user_end_year);
	fillMonthes(document.getElementById('user_begin_month'),user_begin_month);
	fillMonthes(document.getElementById('user_end_month'),user_end_month);
	fillDays(document.getElementById('user_begin_day'),document.getElementById('user_begin_month'),user_begin_day);
	fillDays(document.getElementById('user_end_day'),document.getElementById('user_end_month'),user_end_day);
}

function switchFormState() {
	var formDisabled = !document.getElementById('set_period').checked;
   	document.getElementById('user_begin_day').disabled = formDisabled;
   	document.getElementById('user_begin_month').disabled = formDisabled;
   	document.getElementById('user_begin_year').disabled = formDisabled;
   	document.getElementById('user_end_day').disabled = formDisabled;
   	document.getElementById('user_end_month').disabled = formDisabled;
   	document.getElementById('user_end_year').disabled = formDisabled;
}

function fillYears(element,value) {
	var curYear = (new Date()).getFullYear();
	var minYear = curYear - 10 / 2;
	for(var i=minYear; i<minYear+10; i++) {
		var option = document.createElement('OPTION');
		option.innerHTML = i;
		option.value = i;
		if (i == value) option.selected = true;
    	element.appendChild(option);
	}
}

function fillMonthes(element,value) {
	for(var i=0; i<monthes.length; i++) {
		var option = document.createElement('OPTION');
		option.innerHTML = monthes[i];
		option.value = i+1;
		option.selected = i+1 == value;
    	element.appendChild(option);
	}
}

function fillDays(element,monthEl,value) {
	var curDay = element.value;
	element.innerHTML = '';
	for(var i=1; i<=daysInMonth[monthEl.value-1]; i++) {
		var option = document.createElement('OPTION');
		option.innerHTML = i;
		option.value = i;
		option.selected = i == value;
    	element.appendChild(option);
	}
	if (curDay) element.value = curDay;
}