public static function getGravatar($email, $size = 80, $default = 'mm', $rating = 'g', $attributes = [])
    {
        $attr = trim(self::arrayToString($attributes));

        $url = 'https://www.gravatar.com/';

        return sprintf(
            '<img src="%savatar.php?gravatar_id=%s&default=%s&size=%s&rating=%s" width="%spx" height="%spx" %s />',
            $url,
            md5(strtolower(trim($email))),
            $default,
            $size,
            $rating,
            $size,
            $size,
            $attr
        );
    }