function move_back(day) {
    var year_id = document.all["calendar_year"].selectedIndex;
    var month   = document.all["calendar_month"][document.all["calendar_month"].selectedIndex].value;

    if (month == 1) {
        if (year_id != 0) {
            var year = document.all["calendar_year"][year_id - 1].value;
            month    = 12;
        } else {
            var year = document.all["calendar_year"][year_id].value;
        }
    } else {
        month--;
        var year = document.all["calendar_year"][year_id].value;
    }

    window.location = "index.php?year=" + year + "&month=" + month + "&day=" + day;
}

function move_front(day) {
    var year_id = document.all["calendar_year"].selectedIndex;
    var month   = document.all["calendar_month"][document.all["calendar_month"].selectedIndex].value;

    if (month == 12) {
        if (year_id != document.all["calendar_year"].length - 1) {
            var year = document.all["calendar_year"][year_id + 1].value;
            month    = 1;
        } else {
            var year = document.all["calendar_year"][year_id].value;
        }
    } else {
        month++;
        var year = document.all["calendar_year"][year_id].value;
    }

    window.location = "index.php?year=" + year + "&month=" + month + "&day=" + day;
}

function move_month_year(day) {
    var year  = document.all["calendar_year"][document.all["calendar_year"].selectedIndex].value;
    var month = document.all["calendar_month"][document.all["calendar_month"].selectedIndex].value;

    window.location = "index.php?year=" + year + "&month=" + month + "&day=" + day;
}