fs: add abstractions for reading all text and enum dir

Add abstractions to the IFileSystem interface for enumerating
directories and reading the entire contents of a file to a string.

Author: mjcheetham

src/shared/Core/FileSystem.cs

@@ -84,6 +84,29 @@ public interface IFileSystem
         /// </returns>
         IEnumerable<string> EnumerateFiles(string path, string searchPattern);
 
+        /// <summary>
+        /// Returns an enumerable collection of directory full names in a specified path.
+        /// </summary>
+        /// <param name="path">The relative or absolute path to the directory to search. This string is not case-sensitive.</param>
+        /// <returns>
+        /// An enumerable collection of the full names (including paths) for the directories
+        /// in the directory specified by path.
+        /// </returns>
+        IEnumerable<string> EnumerateDirectories(string path);
+
+        /// <summary>
+        /// Opens a text file, reads all the text in the file, and then closes the file
+        /// </summary>
+        /// <param name="path">The file to open for reading.</param>
+        /// <returns>A string containing all the text in the file.</returns>
+        string ReadAllText(string path);
+
+        /// <summary>
+        /// Opens a text file, reads all lines of the file, and then closes the file.
+        /// </summary>
+        /// <param name="path">The file to open for reading.</param>
+        /// <returns>A string array containing all lines of the file.</returns>
+        string[] ReadAllLines(string path);
     }
 
     /// <summary>
@@ -111,5 +134,11 @@ public Stream OpenFileStream(string path, FileMode fileMode, FileAccess fileAcce
         public void DeleteFile(string path) => File.Delete(path);
 
         public IEnumerable<string> EnumerateFiles(string path, string searchPattern) => Directory.EnumerateFiles(path, searchPattern);
+
+        public IEnumerable<string> EnumerateDirectories(string path) => Directory.EnumerateDirectories(path);
+
+        public string ReadAllText(string path) => File.ReadAllText(path);
+
+        public string[] ReadAllLines(string path) => File.ReadAllLines(path);
     }
 }

src/shared/TestInfrastructure/Objects/TestFileSystem.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Text;
 using System.Text.RegularExpressions;
 
 namespace GitCredentialManager.Tests.Objects
@@ -92,6 +93,41 @@ bool IsPatternMatch(string s, string p)
             }
         }
 
+        IEnumerable<string> IFileSystem.EnumerateDirectories(string path)
+        {
+            StringComparison comparer = IsCaseSensitive
+                ? StringComparison.Ordinal
+                : StringComparison.OrdinalIgnoreCase;
+
+            foreach (var dirPath in Directories)
+            {
+                if (dirPath.StartsWith(path, comparer))
+                {
+                    yield return dirPath;
+                }
+            }
+        }
+
+        string IFileSystem.ReadAllText(string path)
+        {
+            if (Files.TryGetValue(path, out byte[] data))
+            {
+                return Encoding.UTF8.GetString(data);
+            }
+
+            throw new IOException("File not found");
+        }
+
+        string[] IFileSystem.ReadAllLines(string path)
+        {
+            if (Files.TryGetValue(path, out byte[] data))
+            {
+                return Encoding.UTF8.GetString(data).Split(new[] { "\r\n", "\n" }, StringSplitOptions.None);
+            }
+
+            throw new IOException("File not found");
+        }
+
         #endregion
 
         /// <summary>