var CurMonth = new Date().getMonth();
var CurYear = new Date().getFullYear();
var MonName = ['Январь', 'Февраль', 'Март', 'Апрель', 'Май', 'Июнь',
    'Июль', 'Август', 'Сентябрь', 'Октябрь', 'Ноябрь', 'Декабрь'];

function DrawCal(Month, Year) {
    if (Month > 11) {
        Month = 0;
        Year += 1;
    } else if (Month < 0) {
        Month = 11;
        Year -= 1;
    }
    CurMonth = Month;
    CurYear = Year;

    var calendar = document.getElementById('calendar');
    calendar.innerHTML = '';
    document.getElementById('headerMonth').innerHTML = MonName[Month];
    document.getElementById('headerYear').innerHTML = CurYear;

    var WeekDay = (new Date(Year, Month, 1).getDay() - 1 + 7) % 7;
    var Today = new Date();
    var DayNum = new Date(Year, Month + 1, 0).getDate();

    for (var week = 0; week < 6; week++) {
        var tr = document.createElement('tr');
        for (var day = 0; day < 7; day++){
            var td = document.createElement('td');
            tr.appendChild(td);
            var index = week * 7 + day;
            if (index < WeekDay + DayNum && index >= WeekDay) {
                td.innerHTML = index + 1 - WeekDay;
                td.onclick = function() {
                    var prevEl = document.getElementById('curday');
                    if (prevEl)
                        prevEl.id = '';
                    if (this != prevEl)
                        this.id = 'curday';
                };
                if (td.innerHTML == Today.getDate() && Month == Today.getMonth() && Year == Today.getFullYear())
                    td.className = 'cday';
            }
            else
                td.innerHTML = '&nbsp;';
        }
        calendar.appendChild(tr);
    }
}

function InitCal() {
    DrawCal(CurMonth, CurYear);
    var Calselect = document.getElementById('Calselect');
    for (var i = 1980; i < 2021; i++) {
        var option = document.createElement('option');
        Calselect.appendChild(option);
        option.value = i;
        option.innerHTML = i;
    }
}