public static function now(?string $timezone = null): Date
    {
        $timezone = $timezone ?: date_default_timezone_get();
        assert(Validate::isTimezone($timezone), sprintf('Invalid timezone: %s', $timezone));

        $dateTime = new DateTimeImmutable('now', new DateTimeZone($timezone));
        $year = (int) $dateTime->format('Y');
        $month = (int) $dateTime->format('n');
        $day = (int) $dateTime->format('j');

        return new static($year, $month, $day);
    }