3 files changed, 95 insertions, 0 deletions
diff --git a/src/DotNetOpenAuth.BuildTasks/DotNetOpenAuth.BuildTasks.csproj b/src/DotNetOpenAuth.BuildTasks/DotNetOpenAuth.BuildTasks.csproj
index 7f84787..e41b1e6 100644
--- a/src/DotNetOpenAuth.BuildTasks/DotNetOpenAuth.BuildTasks.csproj
+++ b/src/DotNetOpenAuth.BuildTasks/DotNetOpenAuth.BuildTasks.csproj
@@ -95,6 +95,7 @@
     <Compile Include="CheckAdminRights.cs" />
     <Compile Include="JsPack.cs" />
     <Compile Include="ParseMaster.cs" />
+    <Compile Include="Purge.cs" />
     <Compile Include="ReSignDelaySignedAssemblies.cs" />
     <Compile Include="SetEnvironmentVariable.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
diff --git a/src/DotNetOpenAuth.BuildTasks/CustomMsBuildTasks.sln b/src/DotNetOpenAuth.BuildTasks/DotNetOpenAuth.BuildTasks.sln
index 6eae4e0..c875882 100644
--- a/src/DotNetOpenAuth.BuildTasks/CustomMsBuildTasks.sln
+++ b/src/DotNetOpenAuth.BuildTasks/DotNetOpenAuth.BuildTasks.sln
@@ -3,6 +3,12 @@ Microsoft Visual Studio Solution File, Format Version 10.00
 # Visual Studio 2008
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "DotNetOpenAuth.BuildTasks", "DotNetOpenAuth.BuildTasks.csproj", "{AC231A51-EF60-437C-A33F-AF8ADEB8EB74}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{ABBE14A3-0404-4123-9093-E598C3DD3E9B}"
+	ProjectSection(SolutionItems) = preProject
+		..\..\build.proj = ..\..\build.proj
+		..\..\lib\DotNetOpenAuth.BuildTasks.targets = ..\..\lib\DotNetOpenAuth.BuildTasks.targets
+	EndProjectSection
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
diff --git a/src/DotNetOpenAuth.BuildTasks/Purge.cs b/src/DotNetOpenAuth.BuildTasks/Purge.cs
new file mode 100644
index 0000000..f23a6d9
--- /dev/null
+++ b/src/DotNetOpenAuth.BuildTasks/Purge.cs
@@ -0,0 +1,88 @@
+//-----------------------------------------------------------------------
+// <copyright file="Purge.cs" company="Andrew Arnott">
+//     Copyright (c) Andrew Arnott. All rights reserved.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace DotNetOpenAuth.BuildTasks {
+	using System;
+	using System.Collections.Generic;
+	using System.Linq;
+	using System.Text;
+	using Microsoft.Build.Utilities;
+	using Microsoft.Build.Framework;
+	using System.IO;
+	using System.Text.RegularExpressions;
+
+	/// <summary>
+	/// Purges directory trees of all directories and files that are not on a whitelist.
+	/// </summary>
+	/// <remarks>
+	/// This task performs a function similar to robocopy's /MIR switch, except that
+	/// this task does not require that an entire directory tree be used as the source
+	/// in order to purge old files from the destination.
+	/// </remarks>
+	public class Purge : Task {
+		/// <summary>
+		/// Initializes a new instance of the <see cref="Purge"/> class.
+		/// </summary>
+		public Purge() {
+			this.PurgeEmptyDirectories = true;
+		}
+
+		/// <summary>
+		/// Gets or sets the root directories to purge.
+		/// </summary>
+		/// <value>The directories.</value>
+		[Required]
+		public string[] Directories { get; set; }
+
+		/// <summary>
+		/// Gets or sets the files that should be NOT be purged.
+		/// </summary>
+		public ITaskItem[] IntendedFiles { get; set; }
+
+		/// <summary>
+		/// Gets or sets a value indicating whether empty directories will be deleted.
+		/// </summary>
+		/// <value>
+		/// 	The default value is <c>true</c>.
+		/// </value>
+		public bool PurgeEmptyDirectories { get; set; }
+
+		/// <summary>
+		/// Executes this instance.
+		/// </summary>
+		public override bool Execute() {
+			HashSet<string> intendedFiles = new HashSet<string>(this.IntendedFiles.Select(file => file.GetMetadata("FullPath")), StringComparer.OrdinalIgnoreCase);
+
+			foreach (string directory in this.Directories.Select(dir => NormalizePath(dir))) {
+				foreach (string existingFile in Directory.GetFiles(directory, "*", SearchOption.AllDirectories)) {
+					if (!intendedFiles.Contains(existingFile)) {
+						this.Log.LogWarning("Purging file \"{0}\".", existingFile);
+						File.Delete(existingFile);
+					}
+				}
+
+				if (this.PurgeEmptyDirectories) {
+					foreach (string subdirectory in Directory.GetDirectories(directory, "*", SearchOption.AllDirectories)) {
+						// We have to check for the existance of the directory because it MAY be
+						// a descendent of a directory we already deleted in this loop.
+						if (Directory.Exists(subdirectory)) {
+							if (Directory.GetDirectories(subdirectory).Length == 0 && Directory.GetFiles(subdirectory).Length == 0) {
+								this.Log.LogWarning("Purging empty directory \"{0}\".", subdirectory);
+								Directory.Delete(subdirectory);
+							}
+						}
+					}
+				}
+			}
+
+			return !this.Log.HasLoggedErrors;
+		}
+
+		private static string NormalizePath(string path) {
+			return Regex.Replace(path, @"\\+", @"\");
+		}
+	}
+}