From 3ce8d281b792ee8e58a66a1f0651711c5fd070f7 Mon Sep 17 00:00:00 2001
From: Oliver Booth <me@olivr.me>
Date: Thu, 30 Mar 2023 17:55:41 +0100
Subject: [PATCH] feat: add TextReader.EnumerateLines/Async

---
 CHANGELOG.md                         |  1 +
 X10D.Tests/src/IO/TextReaderTests.cs | 83 ++++++++++++++++++++++++++++
 X10D/src/IO/TextReaderExtensions.cs  | 53 ++++++++++++++++++
 3 files changed, 137 insertions(+)
 create mode 100644 X10D.Tests/src/IO/TextReaderTests.cs
 create mode 100644 X10D/src/IO/TextReaderExtensions.cs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d88d34e..6ff7772 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -75,6 +75,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - X10D: Added `string.IsWhiteSpace()`.
 - X10D: Added `string.IsNullOrEmpty()`.
 - X10D: Added `string.IsNullOrWhiteSpace()`.
+- X10D: Added `TextReader.EnumerateLines()` and `TextReader.EnumerateLinesAsync()`.
 - X10D: Added `TimeSpan.TryParse(ReadOnlySpan<char>, out TimeSpan)`.
 - X10D: Added `Quaternion.Multiply(Vector3)` - this functions as an equivalent to Unity's `Quaternion * Vector3` operator.
 - X10D: Added `Vector2.Deconstruct()`.
diff --git a/X10D.Tests/src/IO/TextReaderTests.cs b/X10D.Tests/src/IO/TextReaderTests.cs
new file mode 100644
index 0000000..6e10ef4
--- /dev/null
+++ b/X10D.Tests/src/IO/TextReaderTests.cs
@@ -0,0 +1,83 @@
+using System.Text;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.IO;
+
+namespace X10D.Tests.IO;
+
+[TestClass]
+public class TextReaderTests
+{
+    [TestMethod]
+    public void EnumerateLines_ShouldYield10Lines_Given10LineString()
+    {
+        using var stream = new MemoryStream();
+        using (var writer = new StreamWriter(stream, Encoding.UTF8, leaveOpen: true))
+        {
+            for (var index = 0; index < 10; index++)
+            {
+                writer.WriteLine(index);
+            }
+        }
+
+        stream.Position = 0;
+        using var reader = new StreamReader(stream, Encoding.UTF8);
+        var lineCount = 0;
+
+        foreach (string _ in reader.EnumerateLines())
+        {
+            lineCount++;
+        }
+
+        Assert.AreEqual(10, lineCount);
+    }
+
+    [TestMethod]
+    public async Task EnumerateLinesAsync_ShouldYield10Lines_Given10LineString()
+    {
+        using var stream = new MemoryStream();
+        await using (var writer = new StreamWriter(stream, Encoding.UTF8, leaveOpen: true))
+        {
+            for (var index = 0; index < 10; index++)
+            {
+                writer.WriteLine(index);
+            }
+        }
+
+        stream.Position = 0;
+        using var reader = new StreamReader(stream, Encoding.UTF8);
+        var lineCount = 0;
+
+        await foreach (string _ in reader.EnumerateLinesAsync().ConfigureAwait(false))
+        {
+            lineCount++;
+        }
+
+        Assert.AreEqual(10, lineCount);
+    }
+
+    [TestMethod]
+    public void EnumerateLines_ShouldThrowArgumentNullException_GivenNullSource()
+    {
+        TextReader reader = null!;
+        Assert.ThrowsException<ArgumentNullException>(() =>
+        {
+            foreach (string _ in reader.EnumerateLines())
+            {
+                // loop body is intentionally empty
+            }
+        });
+    }
+
+    [TestMethod]
+    public async Task EnumerateLinesAsync_ShouldThrowArgumentNullException_GivenNullSource()
+    {
+        TextReader reader = null!;
+        await Assert.ThrowsExceptionAsync<ArgumentNullException>(async () =>
+        {
+            await foreach (string _ in reader.EnumerateLinesAsync().ConfigureAwait(false))
+            {
+                // loop body is intentionally empty
+            }
+        }).ConfigureAwait(false);
+    }
+}
diff --git a/X10D/src/IO/TextReaderExtensions.cs b/X10D/src/IO/TextReaderExtensions.cs
new file mode 100644
index 0000000..4ecb213
--- /dev/null
+++ b/X10D/src/IO/TextReaderExtensions.cs
@@ -0,0 +1,53 @@
+namespace X10D.IO;
+
+/// <summary>
+///     IO-related extension methods for <see cref="TextReader" />.
+/// </summary>
+public static class TextReaderExtensions
+{
+    /// <summary>
+    ///     Enumerates the lines provided by the current text reader.
+    /// </summary>
+    /// <param name="reader">The reader whose lines to enumerate.</param>
+    /// <returns>An enumerable collection of lines as read from <paramref name="reader" />.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="reader" /> is <see langword="null" />.</exception>
+    public static IEnumerable<string> EnumerateLines(this TextReader reader)
+    {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(reader);
+#else
+        if (reader is null)
+        {
+            throw new ArgumentNullException(nameof(reader));
+        }
+#endif
+
+        while (reader.ReadLine() is { } line)
+        {
+            yield return line;
+        }
+    }
+
+    /// <summary>
+    ///     Asynchronously enumerates the lines provided by the current text reader.
+    /// </summary>
+    /// <param name="reader">The reader whose lines to enumerate.</param>
+    /// <returns>An asynchronous enumerable collection of lines as read from <paramref name="reader" />.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="reader" /> is <see langword="null" />.</exception>
+    public static async IAsyncEnumerable<string> EnumerateLinesAsync(this TextReader reader)
+    {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(reader);
+#else
+        if (reader is null)
+        {
+            throw new ArgumentNullException(nameof(reader));
+        }
+#endif
+
+        while (await reader.ReadLineAsync().ConfigureAwait(false) is { } line)
+        {
+            yield return line;
+        }
+    }
+}