updating to check if the number is actually a credit card using luhn

src/Serilog.Enrichers.Sensitive/CreditCardMaskingOperator.cs

@@ -1,27 +1,71 @@
-using System.Text.RegularExpressions;
+using System;
+using System.Text.RegularExpressions;
 
 namespace Serilog.Enrichers.Sensitive
 {
-	public class CreditCardMaskingOperator : RegexMaskingOperator
-	{
-		private const string CreditCardPartialReplacePattern =
-			@"(?<leading4>\d{4}(?<sep>[ -]?))(?<toMask>\d{4}\k<sep>*\d{2})(?<trailing6>\d{2}\k<sep>*\d{4})";
+    public class CreditCardMaskingOperator : IMaskingOperator
+    {
+        private const string CreditCardPartialReplacePattern =
+            @"(?<leading4>\d{4}(?<sep>[ -]?))(?<toMask>\d{4}\k<sep>*\d{2})(?<trailing6>\d{2}\k<sep>*\d{4})";
 
-		private const string CreditCardFullReplacePattern =
-			@"(?<toMask>\d{4}(?<sep>[ -]?)\d{4}\k<sep>*\d{4}\k<sep>*\d{4})";
+        private const string CreditCardFullReplacePattern =
+            @"(?<toMask>\d{4}(?<sep>[ -]?)\d{4}\k<sep>*\d{4}\k<sep>*\d{4})";
 
-		private readonly string _replacementPattern;
+        private readonly string _replacementPattern;
 
-		public CreditCardMaskingOperator() : this(true)
-		{
-		}
+        public CreditCardMaskingOperator() : this(true)
+        {
+        }
 
-		public CreditCardMaskingOperator(bool fullMask) 
-			: base(fullMask ? CreditCardFullReplacePattern : CreditCardPartialReplacePattern, RegexOptions.IgnoreCase | RegexOptions.Compiled)
-		{
-			_replacementPattern = fullMask ? "{0}" : "${{leading4}}{0}${{trailing6}}";
-		}
+        public CreditCardMaskingOperator(bool fullMask)
+        {
+            _replacementPattern = fullMask ? "{0}" : "${{leading4}}{0}${{trailing6}}";
+        }
 
-		protected override string PreprocessMask(string mask) => string.Format(_replacementPattern, mask);
-	}
+        protected string PreprocessMask(string mask)
+        {
+            return string.Format(_replacementPattern, mask);
+        }
+
+        public MaskingResult Mask(string input, string mask)
+        {
+            var matches = Regex.Matches(input, _replacementPattern);
+            foreach (Match match in matches)
+            {
+                if (IsValidCreditCardNumber(match.Value))
+                {
+                    // Perform masking
+                    input = Regex.Replace(input, match.Value, m => PreprocessMask("XXXX-XXXX-XXXX-XXXX"));
+                    return new MaskingResult { Match = true, Result = input };
+                }
+            }
+            return MaskingResult.NoMatch;
+        }
+
+        private bool IsValidCreditCardNumber(string cardNumber)
+        {
+            // Remove non-numeric characters
+            var cleanCardNumber = Regex.Replace(cardNumber, "[^0-9]", "");
+
+            int sum = 0;
+            bool alternate = false;
+            for (int i = cleanCardNumber.Length - 1; i >= 0; i--)
+            {
+                var digit = int.Parse(cleanCardNumber[i].ToString());
+
+                if (alternate)
+                {
+                    digit *= 2;
+                    if (digit > 9)
+                    {
+                        digit = (digit % 10) + 1;
+                    }
+                }
+                sum += digit;
+                alternate = !alternate;
+            }
+            // If the sum modulo 10 is 0, the number is valid according to the Luhn formula
+            return sum % 10 == 0;
+        }
+    }
 }