protected function determineType()
    {
        if (in_array($this->group, static::$linkGroups)) {
            return 'link';
        }

        if (in_array($this->extension, static::$pictureExtensions)) {
            return 'picture';
        }

        if (in_array($this->extension, static::$videoExtensions)) {
            return 'video';
        }

        return 'document';
    }