feat: Add EnumerateLines extension method (#45)

Author: gigi81

src/System.IO.Abstractions.Extensions/IFileInfoExtensions.cs

@@ -1,4 +1,8 @@
-namespace System.IO.Abstractions
+using System.Collections;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.IO.Abstractions
 {
     public static class IFileInfoExtensions
     {
@@ -12,5 +16,26 @@ public static void ThrowIfNotFound(this IFileInfo info)
             if (!info.Exists)
                 throw new FileNotFoundException(StringResources.Format("COULD_NOT_FIND_FILE_EXCEPTION", info.FullName));
         }
+
+        /// <summary>
+        /// Creates an <see cref="IEnumerable{String}"/> that can enumerate the lines of text in the <paramref name="info"/> file
+        /// </summary>
+        /// <param name="info">File to enumerate content</param>
+        /// <returns>Returns an <see cref="IEnumerable{String}"/> to enumerate the content of the file</returns>
+        public static IEnumerable<string> EnumerateLines(this IFileInfo info)
+        {
+            return new LineEnumerable(info, null);
+        }
+
+        /// <summary>
+        /// Creates an <see cref="IEnumerable{String}"/> that can enumerate the lines of text in the <paramref name="info"/> file
+        /// using the specified <paramref name="encoding"/>
+        /// </summary>
+        /// <param name="info">File to enumerate content</param>
+        /// <returns>Returns an <see cref="IEnumerable{String}"/> to enumerate the content of the file</returns>
+        public static IEnumerable<string> EnumerateLines(this IFileInfo info, Encoding encoding)
+        {
+            return new LineEnumerable(info, encoding);
+        }
     }
 }

src/System.IO.Abstractions.Extensions/LineEnumerator.cs

@@ -0,0 +1,60 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.IO.Abstractions
+{
+    internal sealed class LineEnumerable : IEnumerable<string>
+    {
+        private readonly IFileInfo _file;
+        private readonly Encoding _encoding;
+
+        public LineEnumerable(IFileInfo file, Encoding encoding)
+        {
+            _file = file;
+            _encoding = encoding;
+        }
+
+        public IEnumerator<string> GetEnumerator() => new LineEnumerator(_file, _encoding);
+
+        IEnumerator IEnumerable.GetEnumerator() => new LineEnumerator(_file, _encoding);
+    }
+
+    internal sealed class LineEnumerator : IEnumerator<string>
+    {
+        private Stream _stream;
+        private StreamReader _reader;
+        private string _current;
+
+        public LineEnumerator(IFileInfo file, Encoding encoding)
+        {
+            _stream = file.OpenRead();
+            _reader = encoding == null
+                ? new StreamReader(_stream)
+                : new StreamReader(_stream, encoding);
+        }
+
+        public string Current => _current;
+
+        object IEnumerator.Current => _current;
+
+        public void Dispose()
+        {
+            _reader?.Dispose();
+            _reader = null;
+            _stream?.Dispose();
+            _stream = null;
+        }
+
+        public bool MoveNext()
+        {
+            _current = _reader.ReadLine();
+            return _current != null;
+        }
+
+        public void Reset()
+        {
+            throw new InvalidOperationException();
+        }
+    }
+}

tests/System.IO.Abstractions.Extensions.Tests/FileInfoExtensionsTests.cs

@@ -1,4 +1,7 @@
 using NUnit.Framework;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
 
 namespace System.IO.Abstractions.Extensions.Tests
 {
@@ -43,5 +46,33 @@ public void ThrowIfNotFound_IfFileExists_DoesNotThrowException()
             //cleanup
             file.Delete();
         }
+
+        [TestCase("line1", "line2", "line3")]
+        [TestCase("line1", "", "line3")]
+        public void EnumerateLines_ReadFromExistingFile_ReturnsLines(params string[] content)
+        {
+            //arrange
+            var fs = new FileSystem();
+            var current = fs.DirectoryInfo.New(fs.Directory.GetCurrentDirectory());
+            var guid = Guid.NewGuid().ToString();
+            var file = current.File(guid);
+            //create file
+            using (var stream = file.OpenWrite())
+            using (var writer = new StreamWriter(stream, Encoding.UTF8))
+            {
+                foreach(var line in content)
+                    writer.WriteLine(line);
+            }
+
+            //act
+            var actual = file.EnumerateLines().ToArray();
+
+            //assert
+            Assert.AreEqual(content.Length, actual.Length);
+            for(int i=0; i<content.Length; i++)
+            {
+                Assert.AreEqual(content[i], actual[i]);
+            }
+        }
     }
 }