Add immediate transitions. Add Start() to avoid faffing about with InitialStateOrDefault().

Author: leeoades

FunctionalStateMachine.Core.Tests/StateMachineImmediateTransitionTests.cs

@@ -0,0 +1,110 @@
+namespace FunctionalStateMachine.Core.Tests;
+
+public class StateMachineImmediateTransitionTests
+{
+    [Fact]
+    public void Start_AppliesEntryAndImmediateTransition()
+    {
+        var machine = StateMachine<State, Trigger, Data, Command>.Create()
+            .StartWith(State.Starting)
+            .For(State.Starting)
+                .OnEntry(data => new Command("enter-starting"))
+                .OnExit(data => new Command("exit-starting"))
+                .Immediately()
+                    .TransitionTo(State.Waiting)
+                    .Done()
+            .For(State.Waiting)
+                .OnEntry(data => new Command("enter-waiting"))
+            .Build();
+
+        var (state, _, commands) = machine.Start(Data.Initial);
+
+        Assert.Equal(State.Waiting, state);
+        Assert.Equal(
+            ["enter-starting", "exit-starting", "enter-waiting"],
+            commands.Select(command => command.Message).ToArray());
+    }
+
+    [Fact]
+    public void Fire_AppliesImmediateTransitionsAfterEntry()
+    {
+        var machine = StateMachine<State, Trigger, Data, Command>.Create()
+            .StartWith(State.Starting)
+            .For(State.Starting)
+                .On(Trigger.Next)
+                    .TransitionTo(State.Waiting)
+            .For(State.Waiting)
+                .OnEntry(data => new Command("enter-waiting"))
+                .Immediately()
+                    .TransitionTo(State.Ready)
+                    .Done()
+            .For(State.Ready)
+                .OnEntry(data => new Command("enter-ready"))
+            .Build();
+
+        var (nextState, _, commands) = machine.Fire(Trigger.Next, State.Starting, Data.Initial);
+
+        Assert.Equal(State.Ready, nextState);
+        Assert.Equal(
+            ["enter-waiting", "enter-ready"],
+            commands.Select(command => command.Message).ToArray());
+    }
+
+    [Fact]
+    public void ImmediateTransitionGuard_CanBlockTransition()
+    {
+        var machine = StateMachine<State, Trigger, Data, Command>.Create()
+            .StartWith(State.Starting)
+            .For(State.Starting)
+                .Immediately()
+                    .Guard(data => data.Value == "go")
+                    .TransitionTo(State.Waiting)
+                    .Done()
+            .For(State.Waiting)
+            .Build();
+
+        var (state, _, commands) = machine.Start(new Data("stop"));
+
+        Assert.Equal(State.Starting, state);
+        Assert.Empty(commands);
+    }
+
+    [Fact]
+    public void ImmediateTransitionLoop_Throws()
+    {
+        var machine = StateMachine<State, Trigger, Data, Command>.Create()
+            .StartWith(State.Starting)
+            .For(State.Starting)
+                .Immediately()
+                    .TransitionTo(State.Waiting)
+                    .Done()
+            .For(State.Waiting)
+                .Immediately()
+                    .TransitionTo(State.Starting)
+                    .Done()
+            .Build();
+
+        var exception = Assert.Throws<InvalidOperationException>(() => machine.Start(Data.Initial));
+
+        Assert.Contains("Immediate transition loop", exception.Message);
+    }
+
+    private enum State
+    {
+        Starting,
+        Waiting,
+        Ready
+    }
+
+    private enum Trigger
+    {
+        Next
+    }
+
+    private sealed record Data(string Value)
+    {
+        public static Data Initial => new(string.Empty);
+    }
+
+    private sealed record Command(string Message);
+}

FunctionalStateMachine.Core/README.md

@@ -26,6 +26,7 @@ Features:
 - Fluent syntax
 - No external dependencies
 - Enter and Exit actions
+- Immediate transitions
 - Hierarchical states
 - Fast, efficient rehydration