public static class HideSensitiveInfoExtension
{
    /// <summary>
    /// 隱藏敏感資訊
    /// </summary>
    /// <param name="info">資訊實體</param>
    /// <param name="left">左邊保留的字元數</param>
    /// <param name="right">右邊保留的字元數</param>
    /// <param name="basedOnLeft">當長度異常時，是否顯示左邊 
 
</param>
    /// <returns></returns>
    public static string HideSensitiveInfo(this string info, int left, int right, bool basedOnLeft = true)
    {
        if (String.IsNullOrEmpty(info))
        {
            return "";
        }
        StringBuilder sbText = new StringBuilder();
        
 
int hiddenCharCount = info.Length - left - right;
        if (hiddenCharCount > 0)
        {
            string prefix = info.Substring(0, left), suffix = info.Substring(info.Length - right);
            sbText.Append(prefix);
            for (int i = 0; i < hiddenCharCount; i++)
            {
                sbText.Append(
 
"*");
            }
            sbText.Append(suffix);
        }
        else
        {
            if (basedOnLeft)
            {
                if (info.Length > left && left > 0)
                {
                    sbText.Append(info.Substring(0, left) + "****");
                }
                else
                {
                    sbText.Append(info.Substring(0, 1) + "****");
                }
            }
            else
            {
                if (info.Length > right && right > 0)
                {
                    sbText.Append("****" + info.Substring(info.Length - right));
                }
                else
                {
                    sbText.Append("****" + info.Substring(info.Length - 1));
                }
            }
        }
        return sbText.ToString();
    }
 
    /// <summary>
    /// 隱藏敏感資訊
    /// </summary>
    /// <param name="info">資訊</param>
    /// <param name="sublen">資訊總長與左子串（或右子串）的比例</param>
    /// <param name="basedOnLeft">當長度異常時，是否顯示左邊，預設true，預設顯示左邊</param>
    /// <code>true</code>顯示左邊，<code>false</code>顯示右邊
    /// <returns></returns>
    public static string HideSensitiveInfo(this string info, int sublen = 3, bool basedOnLeft = true)
    {
        if (String.IsNullOrEmpty(info))
        {
            return "";
        }
        if (sublen <= 1)
        {
            sublen = 3;
        }
        int subLength = info.Length / sublen;
        if (subLength > 0 && info.Length > (subLength * 2))
        {
            string prefix = info.Substring(0, subLength), suffix = info.Substring(info.Length - subLength);
            return prefix + "****" + suffix;
        }
        else
        {
            if (basedOnLeft)
            {
                string prefix = subLength > 0 ? info.Substring(0, subLength) : info.Substring(0, 1);
                return prefix + "****";
            }
            else
            {
                string suffix = subLength > 0 ? info.Substring(info.Length - subLength) : info.Substring(info.Length - 1);
                return "****" + suffix;
            }
        }
    }
 
    /// <summary>
    /// 隱藏郵件詳情
    /// </summary>
    /// <param name="email">郵件地址</param>
    /// <param name="left">郵件頭保留字元個數，預設值設定為3</param>
    /// <returns></returns>
    public static string HideEmailDetails(this string email, int left = 3)
    {
        if (String.IsNullOrEmpty(email))
        {
            return "";
        }
        if (System.Text.RegularExpressions.Regex.IsMatch(email, @"\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"))//如果是郵件地址
        {
            int suffixLen = email.Length - email.LastIndexOf('@');
            return HideSensitiveInfo(email, left, suffixLen, false);
        }
        else
        {
            return HideSensitiveInfo(email);
        }
    }
}