I need to mask the last 4 digits but not hyphen (-) in a credit card number.

For example if I have a string like “1234-5678-9123-4567-891”, the output should be “xxxx-xxxx-xxxx-xxx7-891”. If I have a string like “1234-5678-9123-4567” then the output should be “xxxx-xxxx-xxxx-4567” and for a string like “123456789123” the output should be “xxxxxxxx9123”.

In any case the last 4 digits should be visible. If in a odd string (just like first example), the last 4 digits including hyphen(if any) should be visible.

Thanks

Tried below but not working in all cases—

 public static string MaskCreditCardNo(this string value)
 {
     if (string.IsNullOrWhiteSpace(value))
         return value;

     return Regex.Replace(value, "(\d[\s|-]?){10,}\d", match=>
         {
             string CCnumber = match.Value;
             string digits = string.Concat(CCnumber
          .Where(c => char.IsDigit(c)));
             return (digits.Length >= 12 && digits.Length <= 19) ?
             Regex.Replace(CCnumber.Substring(0, CCnumber.Length - 4), @"d", "x") + CCnumber.Substring(CCnumber.Length - 4) : match.Value;
     });
 }