[SystemExtensions] ToSnakeCase()

Author: flyingpie

src/10-Core/Wtq.UnitTest/Utils/SystemExtensionsTest.cs

@@ -13,4 +13,28 @@ public void EmptyOrWhiteSpaceToNull(string inp, string expected)
 	{
 		Assert.AreEqual(expected, inp.EmptyOrWhiteSpaceToNull());
 	}
+
+	[TestMethod]
+	[DataRow("", "")]
+	[DataRow(" ", " ")]
+	[DataRow("a", "a")]
+	[DataRow("A", "a")]
+	[DataRow("aa", "aa")]
+	[DataRow("Aa", "aa")]
+	[DataRow("AA", "a_a")]
+	[DataRow("Snake", "snake")]
+	[DataRow("SNAKE", "s_n_a_k_e")]
+	[DataRow("ToSnakeCase", "to_snake_case")]
+	[DataRow("to_snake_case", "to_snake_case")]
+	[DataRow("To_Snake_Case", "to__snake__case")]
+	public void ToSnakeCase(string inp, string expected)
+	{
+		Assert.AreEqual(expected, inp.ToSnakeCase());
+	}
+
+	[TestMethod]
+	public void ToSnakeCaseNull()
+	{
+		Assert.ThrowsException<ArgumentNullException>(() => ((string)null).ToSnakeCase());
+	}
 }

src/10-Core/Wtq/Utils/SystemExtensions.cs

@@ -20,13 +20,49 @@ public static IEnumerable<ValidationResult> Validate(this IValidatableObject val
 		return validatable.Validate(new ValidationContext(new object()));
 	}
 
-	public static string ExpandEnvVars(this string? src)
+	/// <summary>
+	/// Replace variables such as "%ENV_VAR%".<br/>
+	/// E.g. "User %USER% is logged in" => "User username1 is logged in".<br/>
+	/// Also replaces "~" with the path to the user's home directory.
+	/// </summary>
+	public static string ExpandEnvVars(this string source)
 	{
-		src ??= string.Empty;
+		Guard.Against.Null(source);
 
 		return Environment
-				.ExpandEnvironmentVariables(src)
+				.ExpandEnvironmentVariables(source)
 				?.Replace("~", WtqPaths.UserHome)
 			?? string.Empty;
 	}
+
+	/// <summary>
+	/// "ToSnakeCase" => "to_snake_case".
+	/// </summary>
+	public static string ToSnakeCase(this string source)
+	{
+		Guard.Against.Null(source);
+
+		if (source.Length <= 1)
+		{
+			return source.ToLowerInvariant();
+		}
+
+		var sb = new StringBuilder();
+		sb.Append(char.ToLowerInvariant(source[0]));
+		for (var i = 1; i < source.Length; ++i)
+		{
+			var c = source[i];
+			if (char.IsUpper(c))
+			{
+				sb.Append('_');
+				sb.Append(char.ToLowerInvariant(c));
+			}
+			else
+			{
+				sb.Append(c);
+			}
+		}
+
+		return sb.ToString();
+	}
 }