C# 獲取頂級（一級）功能變數名稱方法

   /// <summary>
        /// 獲取功能變數名稱的頂級功能變數名稱
        /// </summary>
        /// <param name="domain"></param>
        /// <returns></returns>
        public static string GetTopDomainName(string domain)
        {
            //https://www.safsd.asdfasdf.baidu.com.cn/ssssd/s/b/d/hhh.html?domain=sfsdf.com.cn&id=1
            domain = domain.Trim().ToLower();
            string rootDomain = ".com.cn|.gov.cn|.cn|.com|.net|.org|.so|.co|.mobi|.tel|.biz|.info|.name|.me|.cc|.tv|.asiz|.hk";
            if (domain.StartsWith("http://")) domain = domain.Replace("http://", "");
            if (domain.StartsWith("https://")) domain = domain.Replace("https://", "");
            if (domain.StartsWith("www.")) domain = domain.Replace("www.", "");
            //safsd.asdfasdf.baidu.com.cn/ssssd/s/b/d/hhh.html?domain=sfsdf.com.cn&id=1
            if (domain.IndexOf("/") > 0)
                domain = domain.Substring(0, domain.IndexOf("/"));
            //safsd.asdfasdf.baidu.com.cn
            foreach (string item in rootDomain.Split('|'))
            {
                if (domain.EndsWith(item))
                {
                    domain = domain.Replace(item, "");
                    if (domain.LastIndexOf(".") > 0)//adfasd.asdfas.cn
                    {
                        domain = domain.Replace(domain.Substring(0, domain.LastIndexOf(".") + 1), "");
                    }
                    return domain + item;
                }
                continue;
            }
            return "";
        }