Merge pull request #6 from wlindley/command-chain-failure

Adding OnFailure to Command chains

Bantam/CommandChain.cs

@@ -9,6 +9,7 @@ namespace Bantam
 	public abstract class CommandChain
 	{
 		internal List<CommandAllocator> Commands = new List<CommandAllocator>();
+		internal CommandAllocator FailureCommand;
 	}
 
 	public class CommandChain<T> : CommandChain where T : class, Event
@@ -18,5 +19,10 @@ public class CommandChain<T> : CommandChain where T : class, Event
 			Commands.Add(new CommandAllocator<T, U>(initializer));
 			return this;
 		}
+
+		public void OnFailure<U>(CommandInitializer<U, T> initializer = null) where U : Command, new()
+		{
+			FailureCommand = new CommandAllocator<T, U>(initializer);
+		}
 	}
 }

Bantam/CommandChainExecutor.cs

@@ -50,6 +50,8 @@ internal class EventCommandChainExecutor : CommandChainExecutor
 		private CommandRelay manager;
 		private Event triggeringEvent;
 		private List<CommandAllocator>.Enumerator enumerator;
+		private CommandAllocator failureAllocator;
+		private CommandAllocator currentAllocator;
 		private ObjectPool pool;
 		private Command currentCommand;
 
@@ -60,21 +62,24 @@ public void Reset()
 			currentCommand = null;
 			pool = null;
 			enumerator.Dispose();
+			failureAllocator = null;
+			currentAllocator = null;
 		}
 
 		internal void Start(Event triggeringEvent, CommandChain chain, CommandRelay manager, ObjectPool pool)
 		{
 			this.triggeringEvent = triggeringEvent;
 			this.manager = manager;
 			this.pool = pool;
+			failureAllocator = chain.FailureCommand;
 			enumerator = chain.Commands.GetEnumerator();
 			enumerator.MoveNext();
 			Next();
 		}
 
 		public void CurrentCommandComplete()
 		{
-			enumerator.Current.FreeCommand(pool, currentCommand);
+			currentAllocator.FreeCommand(pool, currentCommand);
 			currentCommand = null;
 			if (enumerator.MoveNext())
 				Next();
@@ -84,14 +89,30 @@ public void CurrentCommandComplete()
 
 		public void CurrentCommandFailed()
 		{
-			enumerator.Current.FreeCommand(pool, currentCommand);
+			currentAllocator.FreeCommand(pool, currentCommand);
 			currentCommand = null;
-			manager.CompleteChainExecution<EventCommandChainExecutor>(this);
+			if (null != failureAllocator)
+				ExecuteFailureCommand();
+			else
+				manager.CompleteChainExecution<EventCommandChainExecutor>(this);
 		}
 
 		private void Next()
 		{
-			currentCommand = enumerator.Current.AllocateCommand(pool, triggeringEvent);
+			currentAllocator = enumerator.Current;
+			StartCommandFromCurrentAllocator();
+		}
+
+		private void ExecuteFailureCommand()
+		{
+			currentAllocator = failureAllocator;
+			failureAllocator = null;
+			StartCommandFromCurrentAllocator();
+		}
+
+		void StartCommandFromCurrentAllocator()
+		{
+			currentCommand = currentAllocator.AllocateCommand(pool, triggeringEvent);
 			currentCommand.Start(this);
 		}
 	}

BantamTest/CommandRelayTest.cs

@@ -76,6 +76,33 @@ public void LaunchRunsInitializerOnCommandIfProvided()
 			testObj.Launch<DummyCommand>(cmd => cmd.value = 7500);
 			Assert.AreEqual(7500, DummyCommand.LastValue);
 		}
+
+		[Test]
+		public void OnFailureExecutesCommandWhenChainFails()
+		{
+			testObj.On<DummyEvent>().Do<FailingCommand>().OnFailure<DummyCommand>();
+			eventBus.Dispatch<DummyEvent>();
+			Assert.AreEqual(1, DummyCommand.ExecuteCount);
+		}
+
+		[Test]
+		public void OnFailureCommandCanFailWithoutCreatingInfiniteRecursion()
+		{
+			testObj.On<DummyEvent>().Do<FailingCommand>().OnFailure<FailingCommand>();
+			eventBus.Dispatch<DummyEvent>();
+		}
+
+		[Test]
+		public void OnFailureCanTakeAnOptionalInitializerForCommand()
+		{
+			var expectedValue = 55;
+			testObj.On<DummyEvent>().Do<FailingCommand>().OnFailure<DummyCommand>((cmd, evt) =>
+				{
+					cmd.value = evt.value;
+				});
+			eventBus.Dispatch<DummyEvent>(evt => evt.value = expectedValue);
+			Assert.AreEqual(expectedValue, DummyCommand.LastValue);
+		}
 	}
 
 	public class DummyCommand : Command

README.md

@@ -29,6 +29,11 @@ commandRelay.On<LoginEvent>()
 	.Do<ShowUsernameCommand>((cmd, evt) => cmd.loginEvent = evt)
 	.Do<ShowOptionsCommand>();
 
+//Handle a failed command chain
+commandRelay.On<UserDataRequestEvent>()
+	.Do<FailingCommand>()
+	.OnFailure<ResetUserDataCommand>();
+
 //Create a Model.
 modelRegistry.Create<UserDataModel>(mdl => mdl.username = "Jane Doe");
 ```