Deduplicate the delimiter-separated casing validators

Semantics.Strings/Validation/Attributes/Casing/IsKebabCaseAttribute.cs

@@ -3,7 +3,6 @@
 namespace ktsu.Semantics.Strings;
 
 using System;
-using System.Linq;
 
 /// <summary>
 /// Validates that a string is in kebab-case (lowercase words separated by hyphens)
@@ -34,38 +33,7 @@ private sealed class KebabCaseValidator : ValidationAdapter
 		/// </summary>
 		/// <param name="value">The string value to validate</param>
 		/// <returns>A validation result indicating success or failure</returns>
-		protected override ValidationResult ValidateValue(string value)
-		{
-			if (string.IsNullOrEmpty(value))
-			{
-				return ValidationResult.Success();
-			}
-
-			// Cannot start or end with hyphen
-			if (value.StartsWith('-') || value.EndsWith('-'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// Cannot have consecutive hyphens
-			if (value.Contains("--"))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// No spaces, underscores, or other separators allowed (except hyphens)
-			if (value.Any(c => char.IsWhiteSpace(c) || c == '_'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// All characters must be lowercase letters, digits, or hyphens
-			if (!value.All(c => char.IsLower(c) || char.IsDigit(c) || c == '-'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			return ValidationResult.Success();
-		}
+		protected override ValidationResult ValidateValue(string value) =>
+			DelimitedCaseValidation.Validate(value, '-', '_', char.IsLower, FailureMessage);
 	}
 }

Semantics.Strings/Validation/Attributes/Casing/IsMacroCaseAttribute.cs

@@ -3,7 +3,6 @@
 namespace ktsu.Semantics.Strings;
 
 using System;
-using System.Linq;
 
 /// <summary>
 /// Validates that a string is in MACRO_CASE (uppercase words separated by underscores)
@@ -35,38 +34,7 @@ private sealed class MacroCaseValidator : ValidationAdapter
 		/// </summary>
 		/// <param name="value">The string value to validate</param>
 		/// <returns>A validation result indicating success or failure</returns>
-		protected override ValidationResult ValidateValue(string value)
-		{
-			if (string.IsNullOrEmpty(value))
-			{
-				return ValidationResult.Success();
-			}
-
-			// Cannot start or end with underscore
-			if (value.StartsWith('_') || value.EndsWith('_'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// Cannot have consecutive underscores
-			if (value.Contains("__"))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// No spaces, hyphens, or other separators allowed (except underscores)
-			if (value.Any(c => char.IsWhiteSpace(c) || c == '-'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// All characters must be uppercase letters, digits, or underscores
-			if (!value.All(c => char.IsUpper(c) || char.IsDigit(c) || c == '_'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			return ValidationResult.Success();
-		}
+		protected override ValidationResult ValidateValue(string value) =>
+			DelimitedCaseValidation.Validate(value, '_', '-', char.IsUpper, FailureMessage);
 	}
 }

Semantics.Strings/Validation/Attributes/Casing/IsSnakeCaseAttribute.cs

@@ -3,7 +3,6 @@
 namespace ktsu.Semantics.Strings;
 
 using System;
-using System.Linq;
 
 /// <summary>
 /// Validates that a string is in snake_case (lowercase words separated by underscores)
@@ -34,38 +33,7 @@ private sealed class SnakeCaseValidator : ValidationAdapter
 		/// </summary>
 		/// <param name="value">The string value to validate</param>
 		/// <returns>A validation result indicating success or failure</returns>
-		protected override ValidationResult ValidateValue(string value)
-		{
-			if (string.IsNullOrEmpty(value))
-			{
-				return ValidationResult.Success();
-			}
-
-			// Cannot start or end with underscore
-			if (value.StartsWith('_') || value.EndsWith('_'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// Cannot have consecutive underscores
-			if (value.Contains("__"))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// No spaces, hyphens, or other separators allowed (except underscores)
-			if (value.Any(c => char.IsWhiteSpace(c) || c == '-'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			// All characters must be lowercase letters, digits, or underscores
-			if (!value.All(c => char.IsLower(c) || char.IsDigit(c) || c == '_'))
-			{
-				return ValidationResult.Failure(FailureMessage);
-			}
-
-			return ValidationResult.Success();
-		}
+		protected override ValidationResult ValidateValue(string value) =>
+			DelimitedCaseValidation.Validate(value, '_', '-', char.IsLower, FailureMessage);
 	}
 }

Semantics.Strings/Validation/DelimitedCaseValidation.cs

@@ -0,0 +1,62 @@
+// Copyright (c) 2023-2026 ktsu-dev contributors
+
+namespace ktsu.Semantics.Strings;
+
+using System;
+using System.Linq;
+
+/// <summary>
+/// The shared rules for the delimiter-separated casing conventions — kebab-case, snake_case and
+/// MACRO_CASE — which differ only in the delimiter they use, the delimiter they forbid, and the
+/// letter case they require.
+/// </summary>
+internal static class DelimitedCaseValidation
+{
+	/// <summary>
+	/// Validates a delimiter-separated casing convention.
+	/// </summary>
+	/// <param name="value">The string value to validate.</param>
+	/// <param name="delimiter">The delimiter the convention separates words with.</param>
+	/// <param name="foreignDelimiter">The delimiter belonging to a different convention, which must not appear.</param>
+	/// <param name="isExpectedCase">Predicate matching the letter case the convention requires.</param>
+	/// <param name="failureMessage">The message reported for every way a value can fail.</param>
+	/// <returns>A validation result indicating success or failure.</returns>
+	internal static ValidationResult Validate(
+		string value,
+		char delimiter,
+		char foreignDelimiter,
+		Func<char, bool> isExpectedCase,
+		string failureMessage)
+	{
+		if (string.IsNullOrEmpty(value))
+		{
+			return ValidationResult.Success();
+		}
+
+		// Cannot start or end with the delimiter.
+		if (value.StartsWith(delimiter) || value.EndsWith(delimiter))
+		{
+			return ValidationResult.Failure(failureMessage);
+		}
+
+		// Cannot have consecutive delimiters.
+		for (int i = 1; i < value.Length; i++)
+		{
+			if (value[i] == delimiter && value[i - 1] == delimiter)
+			{
+				return ValidationResult.Failure(failureMessage);
+			}
+		}
+
+		// No whitespace, and no delimiter belonging to a different convention.
+		if (value.Any(c => char.IsWhiteSpace(c) || c == foreignDelimiter))
+		{
+			return ValidationResult.Failure(failureMessage);
+		}
+
+		// Every character must be an expected-case letter, a digit, or the delimiter.
+		return value.All(c => isExpectedCase(c) || char.IsDigit(c) || c == delimiter)
+			? ValidationResult.Success()
+			: ValidationResult.Failure(failureMessage);
+	}
+}