Add RemoveSeparators method to process strings without separators

The new `RemoveSeparators` extension method removes various separators from a string, such as spaces, dashes, and slashes.
This is particularly useful for handling formatted inputs like credit card numbers.
Updated relevant tests, documentation, and examples to reflect this addition.

Resolves: No entry

Author: shinji-san

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Add `InvalidCharacterException` to throw an exception if the input string contains invalid characters.
+- Add `RemoveSeparators` method to remove all separators from a string. Use it, for example, with credit card numbers.
 
 ### Changed
 - Renamed `Luhn.ConvertAlphaNumericToNumeric` to `Luhn.AlphaNumericToNumeric`

README.md

@@ -274,7 +274,7 @@ namespace Example7
     {
         public static void Main(string[] args)
         {
-            string creditCardNumberWithoutCheckDigit = "4417 1234 5678 911".Replace(" ", "");
+            string creditCardNumberWithoutCheckDigit = "4417 1234 5678 911".RemoveSeparators();
             byte checkDigit = creditCardNumberWithoutCheckDigit.ComputeLuhnCheckDigit();
             Console.WriteLine($"The check digit for credit card number {creditCardNumberWithoutCheckDigit} is: {checkDigit}");
         }

src/Luhn.cs

@@ -37,8 +37,8 @@ namespace LuhnDotNet
     using System.Collections.Generic;
     using System.Diagnostics.CodeAnalysis;
     using System.Globalization;
-#if !NET8_0_OR_GREATER
     using System.Text;
+#if !NET8_0_OR_GREATER
     using System.Text.RegularExpressions;
 #endif
 
@@ -234,6 +234,34 @@ public static bool IsValidLuhnCheckDigit(this byte checkDigit, string number)
 #endif
         }
 
+        /// <summary>
+        /// Removes all separators from the input identifier string.
+        /// </summary>
+        /// <param name="identifier">The input identifier string with separators.</param>
+        /// <returns>The identifier string without separators.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when the input identifier is null or empty.</exception>
+        public static string RemoveSeparators(this string identifier)
+        {
+            if (string.IsNullOrWhiteSpace(identifier))
+            {
+                throw new ArgumentNullException(nameof(identifier), "The identifier cannot be null or empty.");
+            }
+
+            // Define valid separators as a HashSet for O(1) lookup
+            var separators = new HashSet<char> { '/', '\\', '-', '_', '|', ',', ' ', '.' };
+            var result = new StringBuilder();
+
+            foreach (char c in identifier)
+            {
+                if (!separators.Contains(c))
+                {
+                    result.Append(c);
+                }
+            }
+
+            return result.ToString();
+        }
+
         /// <summary>
         /// Converts an alphanumeric string to a numeric string.
         /// </summary>

tests/LuhnTest.cs

@@ -379,5 +379,21 @@ public void ComputeLuhnCheckDigit_WithAlphaNumericToNumeric_ReturnsExpectedCheck
             Assert.Equal(expected, input.AlphaNumericToNumeric().ComputeLuhnCheckDigit());
             Assert.Equal(expected, input.AlphaNumericToNumeric().AsSpan().ComputeLuhnCheckDigit());
         }
+
+        /// <summary>
+        /// Tests that the RemoveSeparators method processes input correctly by removing separators.
+        /// </summary>
+        /// <param name="input">The input string containing separators.</param>
+        /// <param name="expected">The expected string after separators are removed.</param>
+        [Theory]
+        [InlineData("4444 5555 6666 8888", "4444555566668888")]
+        [InlineData("6666/5555/7777/9123", "6666555577779123")]
+        [InlineData(@"6666\5555\7777\9123", "6666555577779123")]
+        [InlineData("4321-5678-9012-3456", "4321567890123456")]
+        [InlineData("0987654321", "0987654321")]
+        public void RemoveSeparators_ValidInput_ReturnsExpectedResult(string input, string expected)
+        {
+            Assert.Equal(expected, input.RemoveSeparators());
+        }
     }
 }