public static string ToSeoUrl(this string url)
        {
            // make the url lowercase
            string encodedUrl = (url ?? "").ToLower();

            // replace & with and
            encodedUrl = Regex.Replace(encodedUrl, @"\&+", "and");

            // remove characters
            encodedUrl = encodedUrl.Replace("'", "");

            // remove invalid characters
            encodedUrl = Regex.Replace(encodedUrl, @"[^a-zآ-ی0-9]", "-");

            // remove duplicates
            encodedUrl = Regex.Replace(encodedUrl, @"-+", "-");

            // trim leading & trailing characters
            encodedUrl = encodedUrl.Trim('-');

            return encodedUrl;
        }