public static function getWeekdayFullname($day = null)
    {
        if ($day === null) {
            $day = new AnDate();
        }
        if ($day instanceof AnDate) {
            $weekday = self::getDayOfWeek($day);
        } elseif (is_int($day)) {
            $weekday = $day;
        }
        $names = self::getWeekDays();
        return $names[$weekday];
    }