Add some more substring extension methods

src/BizHawk.Common/Extensions/StringExtensions.cs

@@ -26,6 +26,18 @@ namespace BizHawk.Common.StringExtensions
 		/// </returns>
 		public static string RemovePrefix(this string str, char prefix, string notFoundValue) => str.Length != 0 && str[0] == prefix ? str.Substring(1, str.Length - 1) : notFoundValue;
 
+		/// <returns>
+		/// <paramref name="str"/> with the leading substring <paramref name="prefix"/> removed, or
+		/// the original <paramref name="str"/> if <paramref name="str"/> does not start with <paramref name="prefix"/>
+		/// </returns>
+		public static string RemovePrefix(this string str, string prefix) => str.RemovePrefix(prefix, notFoundValue: str);
+
+		/// <returns>
+		/// <paramref name="str"/> with the leading substring <paramref name="prefix"/> removed, or
+		/// <paramref name="notFoundValue"/> if <paramref name="str"/> does not start with <paramref name="prefix"/>
+		/// </returns>
+		public static string RemovePrefix(this string str, string prefix, string notFoundValue) => str.StartsWith(prefix) ? str.Substring(prefix.Length, str.Length - prefix.Length) : notFoundValue;
+
 		/// <returns>
 		/// <paramref name="str"/> with the last char removed, or
 		/// the original <paramref name="str"/> if the last char of <paramref name="str"/> is not <paramref name="suffix"/>
@@ -35,6 +47,34 @@ namespace BizHawk.Common.StringExtensions
 				? str.Substring(0, str.Length - 1)
 				: str;
 
+		/// <returns>
+		/// <paramref name="str"/> with the trailing substring <paramref name="suffix"/> removed, or
+		/// the original <paramref name="str"/> if <paramref name="str"/> does not end with <paramref name="suffix"/>
+		/// </returns>
+		public static string RemoveSuffix(this string str, string suffix) => str.RemoveSuffix(suffix, notFoundValue: str);
+
+		/// <returns>
+		/// <paramref name="str"/> with the trailing substring <paramref name="suffix"/> removed, or
+		/// <paramref name="notFoundValue"/> if <paramref name="str"/> does not end with <paramref name="suffix"/>
+		/// </returns>
+		public static string RemoveSuffix(this string str, string suffix, string notFoundValue) => str.EndsWith(suffix) ? str.Substring(0, str.Length - suffix.Length) : notFoundValue;
+
+		/// <returns>
+		/// the substring of <paramref name="str"/> after the first occurrence of <paramref name="delimiter"/>, or
+		/// the original <paramref name="str"/> if not found
+		/// </returns>
+		public static string SubstringAfter(this string str, string delimiter) => str.SubstringAfter(delimiter, notFoundValue: str);
+
+		/// <returns>
+		/// the substring of <paramref name="str"/> after the first occurrence of <paramref name="delimiter"/>, or
+		/// <paramref name="notFoundValue"/> if not found
+		/// </returns>
+		public static string SubstringAfter(this string str, string delimiter, string notFoundValue)
+		{
+			var index = str.IndexOf(delimiter);
+			return index < 0 ? notFoundValue : str.Substring(index + delimiter.Length, str.Length - index - delimiter.Length);
+		}
+
 		/// <returns>
 		/// the substring of <paramref name="str"/> before the first occurrence of <paramref name="delimiter"/>, or
 		/// the original <paramref name="str"/> if not found
@@ -51,6 +91,22 @@ namespace BizHawk.Common.StringExtensions
 			return index < 0 ? notFoundValue : str.Substring(0, index);
 		}
 
+		/// <returns>
+		/// the substring of <paramref name="str"/> before the last occurrence of <paramref name="delimiter"/>, or
+		/// the original <paramref name="str"/> if not found
+		/// </returns>
+		public static string SubstringBeforeLast(this string str, char delimiter) => str.SubstringBeforeLast(delimiter, notFoundValue: str);
+
+		/// <returns>
+		/// the substring of <paramref name="str"/> before the last occurrence of <paramref name="delimiter"/>, or
+		/// <paramref name="notFoundValue"/> if not found
+		/// </returns>
+		public static string SubstringBeforeLast(this string str, char delimiter, string notFoundValue)
+		{
+			var index = str.LastIndexOf(delimiter);
+			return index < 0 ? notFoundValue : str.Substring(0, index);
+		}
+
 		/// <returns>
 		/// the substring of <paramref name="str"/> before the first occurrence of <paramref name="delimiter"/>, or
 		/// <see langword="null"/> if not found

src/BizHawk.Tests/Common/StringExtensions/StringExtensionTests.cs

@@ -6,6 +6,10 @@ namespace BizHawk.Tests.Common.StringExtensions
 	[TestClass]
 	public class StringExtensionTests
 	{
+		private const string abcdef = "abcdef";
+
+		private const string qrs = "qrs";
+
 		[TestMethod]
 		public void In_CaseInsensitive()
 		{
@@ -21,14 +25,62 @@ namespace BizHawk.Tests.Common.StringExtensions
 		[TestMethod]
 		public void TestRemovePrefix()
 		{
-			const string abcdef = "abcdef";
-			const string qrs = "qrs";
-
 			Assert.AreEqual("bcdef", abcdef.RemovePrefix('a', qrs));
 			Assert.AreEqual(string.Empty, "a".RemovePrefix('a', qrs));
 			Assert.AreEqual(qrs, abcdef.RemovePrefix('c', qrs));
 			Assert.AreEqual(qrs, abcdef.RemovePrefix('x', qrs));
 			Assert.AreEqual(qrs, string.Empty.RemovePrefix('a', qrs));
+
+			Assert.AreEqual("def", abcdef.RemovePrefix("abc", qrs));
+			Assert.AreEqual("bcdef", abcdef.RemovePrefix("a", qrs));
+			Assert.AreEqual(abcdef, abcdef.RemovePrefix(string.Empty, qrs));
+			Assert.AreEqual(string.Empty, abcdef.RemovePrefix(abcdef, qrs));
+			Assert.AreEqual(string.Empty, "a".RemovePrefix("a", qrs));
+			Assert.AreEqual(qrs, abcdef.RemovePrefix("c", qrs));
+			Assert.AreEqual(qrs, abcdef.RemovePrefix("x", qrs));
+			Assert.AreEqual(qrs, string.Empty.RemovePrefix("abc", qrs));
+		}
+
+		[TestMethod]
+		public void TestRemoveSuffix()
+		{
+			Assert.AreEqual("abc", abcdef.RemoveSuffix("def", qrs));
+			Assert.AreEqual("abcde", abcdef.RemoveSuffix("f", qrs));
+			Assert.AreEqual(abcdef, abcdef.RemoveSuffix(string.Empty, qrs));
+			Assert.AreEqual(string.Empty, abcdef.RemoveSuffix(abcdef, qrs));
+			Assert.AreEqual(string.Empty, "f".RemoveSuffix("f", qrs));
+			Assert.AreEqual(qrs, abcdef.RemoveSuffix("d", qrs));
+			Assert.AreEqual(qrs, abcdef.RemoveSuffix("x", qrs));
+			Assert.AreEqual(qrs, string.Empty.RemoveSuffix("def", qrs));
+		}
+
+		[TestMethod]
+		public void TestSubstringAfter()
+		{
+			Assert.AreEqual("def", abcdef.SubstringAfter("bc", qrs));
+			Assert.AreEqual(abcdef, abcdef.SubstringAfter(string.Empty, qrs));
+			Assert.AreEqual(string.Empty, abcdef.SubstringAfter(abcdef, qrs));
+			Assert.AreEqual(string.Empty, abcdef.SubstringAfter("f", qrs));
+			Assert.AreEqual(string.Empty, "f".SubstringAfter("f", qrs));
+			Assert.AreEqual("abcdab", "abcdabcdab".SubstringAfter("cd", qrs));
+			Assert.AreEqual(qrs, abcdef.SubstringAfter("x", qrs));
+			Assert.AreEqual(qrs, string.Empty.SubstringAfter("abc", qrs));
+		}
+
+		[TestMethod]
+		public void TestSubstringBefore()
+		{
+			Assert.AreEqual("abc", abcdef.SubstringBefore('d', qrs));
+			Assert.AreEqual(string.Empty, abcdef.SubstringBefore('a', qrs));
+			Assert.AreEqual(string.Empty, "a".SubstringBefore('a', qrs));
+			Assert.AreEqual("abc", "abcdabcdab".SubstringBefore('d', qrs));
+			Assert.AreEqual(qrs, abcdef.SubstringBefore('x', qrs));
+			Assert.AreEqual(qrs, string.Empty.SubstringBefore('d', qrs));
+
+			// fewer tests for SubstringBeforeLast as its implementation should match SubstringBefore, save for using LastIndexOf
+
+			Assert.AreEqual("abcdabc", "abcdabcdab".SubstringBeforeLast('d', qrs));
+			Assert.AreEqual(qrs, "abcdabcdab".SubstringBeforeLast('x', qrs));
 		}
 	}
 }