public static function theme($theme = null)
    {
        if (!self::$_initialized) {
            self::init();
        }

        if ($theme !== null) {
            if (!isset(self::$_themes[$theme])) {
                throw new Exception(__d('wasabi_cms', 'Theme "{0}" does not exist.', $theme));
            }
            self::$_theme = self::$_themes[$theme];
        }

        return self::$_theme;
    }