Established new TopicRepositoryDecorator base class

JeremyCaney · JeremyCaney · commit 799e2b661734 · 2021-01-26T16:15:26.000-08:00
The `ITopicRepository` is a prime candidate for decorators. Decorators require very specific handling to register the underlying implementation and wire-up passthroughs for both events and members. Outside of that, decorators don't require much in terms of implementation, and thus don't benefit from deriving from `TopicRepositoryBase`.

The `TopicRepositoryDecorator` mitigates this by offering a base class just for decorators. It handls all of the wiring so that implementors don't need to worry about that, and can focus exclusively on the parts they need to override.
diff --git a/OnTopic/Repositories/TopicRepositoryDecorator.cs b/OnTopic/Repositories/TopicRepositoryDecorator.cs
@@ -0,0 +1,126 @@
+/*==============================================================================================================================
+| Author        Ignia, LLC
+| Client        Ignia, LLC
+| Project       Topics Library
+\=============================================================================================================================*/
+using System;
+using OnTopic.Internal.Diagnostics;
+using OnTopic.Metadata;
+
+namespace OnTopic.Repositories {
+
+  /*============================================================================================================================
+  | CLASS: TOPIC REPOSITORY DECORATOR
+  \---------------------------------------------------------------------------------------------------------------------------*/
+  /// <summary>
+  ///   Defines a base abstract class for establishing a decorator of an <see cref="ITopicRepository"/>.
+  /// </summary>
+  /// <remarks>
+  ///   Decorators allow implementors to operate off of an underlying version of an <see cref="ITopicRepository"/>, while
+  ///   intercepting calls in order to extend their functionality. They do this by establishing passthrough members to each of
+  ///   the underlying members. The <see cref="TopicRepositoryDecorator"/> offers a base class for implementing decorators by
+  ///   accepting a <see cref="ITopicRepository"/> via its constructor, and then wiring up each of the members as a passthrough.
+  ///   It also subscribes to the underlying <see cref="ITopicRepository"/>'s events so that they will correctly bubble up
+  ///   through the decorator. This way, derived decorators must only implement the specific methods they wish to override, and
+  ///   can leave everything else as is.
+  /// </remarks>
+  public abstract class TopicRepositoryDecorator : ObservableTopicRepository {
+
+    /*==========================================================================================================================
+    | CONSTRUCTOR
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Instantiates a new instance of the <see cref="TopicRepositoryDecorator"/> with a dependency on an underlying <see cref
+    ///   ="ITopicRepository"/> in order to provide necessary data access.
+    /// </summary>
+    /// <param name="topicRepository">
+    ///   A concrete instance of an <see cref="ITopicRepository"/>, which will be used for data access.
+    /// </param>
+    /// <returns>A new instance of the <see cref="TopicRepositoryDecorator"/>.</returns>
+    protected TopicRepositoryDecorator(ITopicRepository topicRepository) : base() {
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Validate input
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      Contract.Requires(topicRepository, "A concrete implementation of an ITopicRepository is required.");
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Set values locally
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      TopicRepository = topicRepository;
+
+      /*------------------------------------------------------------------------------------------------------------------------
+      | Subscribe to underlying events
+      \-----------------------------------------------------------------------------------------------------------------------*/
+      TopicRepository.DeleteEvent += (object sender, DeleteEventArgs args) => OnTopicDeleted(args);
+      TopicRepository.MoveEvent   += (object sender, MoveEventArgs args)   => OnTopicMoved(args);
+      TopicRepository.RenameEvent += (object sender, RenameEventArgs args) => OnTopicRenamed(args);
+
+
+    }
+
+    /*==========================================================================================================================
+    | DATA PROVIDER
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Provides access to the underlying <see cref="ITopicRepository"/> that this decorates.
+    /// </summary>
+    protected ITopicRepository TopicRepository { get; set; }
+
+    /*==========================================================================================================================
+    | GET CONTENT TYPE DESCRIPTORS
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override ContentTypeDescriptorCollection GetContentTypeDescriptors() => TopicRepository.GetContentTypeDescriptors();
+
+    /*==========================================================================================================================
+    | METHOD: LOAD
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override Topic? Load(int topicId, Topic? referenceTopic = null, bool isRecursive = true) =>
+      TopicRepository.Load(topicId, referenceTopic, isRecursive);
+
+    /// <inheritdoc />
+    public override Topic? Load(string? uniqueKey = null, Topic? referenceTopic = null, bool isRecursive = true) =>
+      TopicRepository.Load(uniqueKey, referenceTopic, isRecursive);
+
+    /// <inheritdoc />
+    public override Topic? Load(Topic topic, DateTime version)
+      => TopicRepository.Load(topic, version);
+
+    /// <inheritdoc />
+    public override Topic? Load(int topicId, DateTime version, Topic? referenceTopic = null) =>
+      TopicRepository.Load(topicId, version, referenceTopic);
+
+    /*==========================================================================================================================
+    | METHOD: REFRESH
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override void Refresh(Topic referenceTopic, DateTime since) => TopicRepository.Refresh(referenceTopic, since);
+
+    /*==========================================================================================================================
+    | METHOD: ROLLBACK
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override void Rollback(Topic topic, DateTime version) => TopicRepository.Rollback(topic, version);
+
+    /*==========================================================================================================================
+    | METHOD: SAVE
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override void Save(Topic topic, bool isRecursive = false) => TopicRepository.Save(topic, isRecursive);
+
+    /*==========================================================================================================================
+    | METHOD: MOVE
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override void Move(Topic topic, Topic target, Topic? sibling = null) => TopicRepository.Move(topic, target, sibling);
+
+    /*==========================================================================================================================
+    | METHOD: DELETE
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <inheritdoc />
+    public override void Delete(Topic topic, bool isRecursive) => TopicRepository.Delete(topic, isRecursive);
+
+  } //Class
+} //Namespace
