Allow permitDynamic destination state to be calculated with an async function (Task)

src/Stateless/DynamicTriggerBehaviour.Async.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Stateless
+{
+    public partial class StateMachine<TState, TTrigger>
+    {
+        internal class DynamicTriggerBehaviourAsync : TriggerBehaviour
+        {
+            readonly Func<object[], Task<TState>> _destination;
+            internal Reflection.DynamicTransitionInfo TransitionInfo { get; private set; }
+
+            public DynamicTriggerBehaviourAsync(TTrigger trigger, Func<object[], Task<TState>> destination,
+                TransitionGuard transitionGuard, Reflection.DynamicTransitionInfo info)
+                : base(trigger, transitionGuard)
+            {
+                _destination = destination ?? throw new ArgumentNullException(nameof(destination));
+                TransitionInfo = info ?? throw new ArgumentNullException(nameof(info));
+            }
+
+            public async Task<TState> GetDestinationState(TState source, object[] args)
+            {
+               return await _destination(args);
+            }
+        }
+    }
+}

src/Stateless/Reflection/StateInfo.cs

@@ -72,6 +72,10 @@ internal static void AddRelationships<TState, TTrigger>(StateInfo info, StateMac
                 {
                     dynamicTransitions.Add(((StateMachine<TState, TTrigger>.DynamicTriggerBehaviour)item).TransitionInfo);
                 }
+                foreach (var item in triggerBehaviours.Value.Where(behaviour => behaviour is StateMachine<TState, TTrigger>.DynamicTriggerBehaviourAsync))
+                {
+                    dynamicTransitions.Add(((StateMachine<TState, TTrigger>.DynamicTriggerBehaviourAsync)item).TransitionInfo);
+                }
             }
 
             info.AddRelationships(superstate, substates, fixedTransitions, dynamicTransitions);

src/Stateless/StateMachine.Async.cs

@@ -217,6 +217,15 @@ async Task InternalFireOneAsync(TTrigger trigger, params object[] args)
                         // Handle transition, and set new state
                         var transition = new Transition(source, handler.Destination, trigger, args);
                         await HandleReentryTriggerAsync(args, representativeState, transition);
+                        break;
+                    }
+                case DynamicTriggerBehaviourAsync asyncHandler:
+                    {
+                        var destination = await asyncHandler.GetDestinationState(source, args);
+                        // Handle transition, and set new state; reentry is permitted from dynamic trigger behaviours.
+                        var transition = new Transition(source, destination, trigger, args);
+                        await HandleTransitioningTriggerAsync(args, representativeState, transition);
+
                         break;
                     }
                 case DynamicTriggerBehaviour handler:

src/Stateless/StateMachine.cs

@@ -422,6 +422,18 @@ private void InternalFireOne(TTrigger trigger, params object[] args)
                         HandleReentryTrigger(args, representativeState, transition);
                         break;
                     }
+                case DynamicTriggerBehaviourAsync asyncHandler:
+                    {
+                        asyncHandler.GetDestinationState(source, args)
+                            .ContinueWith(t =>
+                            {
+                                var destination = t.Result;
+                                // Handle transition, and set new state; reentry is permitted from dynamic trigger behaviours.
+                                var transition = new Transition(source, destination, trigger, args);
+                                return HandleTransitioningTriggerAsync(args, representativeState, transition);
+                            });
+                        break;
+                    }
                 case DynamicTriggerBehaviour handler:
                     {
                         handler.GetDestinationState(source, args, out var destination);

test/Stateless.Tests/DotGraphFixture.cs

@@ -5,6 +5,7 @@
 using Xunit;
 using Stateless.Reflection;
 using Stateless.Graph;
+using System.Threading.Tasks;
 
 namespace Stateless.Tests
 {
@@ -196,7 +197,7 @@ public void WhenDiscriminatedByAnonymousGuardWithDescription()
             var expected = Prefix(Style.UML)
                 + Box(Style.UML, "A") + Box(Style.UML, "B")
                 + Line("A", "B", "X [description]")
-                +  suffix;
+                + suffix;
 
             var sm = new StateMachine<State, Trigger>(State.A);
 
@@ -258,6 +259,27 @@ public void DestinationStateIsDynamic()
 
             string dotGraph = UmlDotGraph.Format(sm.GetInfo());
 
+#if WRITE_DOTS_TO_FOLDER
+            System.IO.File.WriteAllText(DestinationFolder + "DestinationStateIsDynamic.dot", dotGraph);
+#endif
+
+            Assert.Equal(expected, dotGraph);
+        }
+
+        [Fact]
+        public void DestinationStateIsDynamicAsync()
+        {
+            var expected = Prefix(Style.UML)
+                + Box(Style.UML, "A")
+                + Decision(Style.UML, "Decision1", "Function")
+                + Line("A", "Decision1", "X") + suffix;
+
+            var sm = new StateMachine<State, Trigger>(State.A);
+            sm.Configure(State.A)
+                .PermitDynamicAsync(Trigger.X, () => Task.FromResult(State.B));
+
+            string dotGraph = UmlDotGraph.Format(sm.GetInfo());
+
 #if WRITE_DOTS_TO_FOLDER
             System.IO.File.WriteAllText(DestinationFolder + "DestinationStateIsDynamic.dot", dotGraph);
 #endif
@@ -280,6 +302,27 @@ public void DestinationStateIsCalculatedBasedOnTriggerParameters()
 
             string dotGraph = UmlDotGraph.Format(sm.GetInfo());
 
+#if WRITE_DOTS_TO_FOLDER
+            System.IO.File.WriteAllText(DestinationFolder + "DestinationStateIsCalculatedBasedOnTriggerParameters.dot", dotGraph);
+#endif
+            Assert.Equal(expected, dotGraph);
+        }
+
+        [Fact]
+        public void DestinationStateIsCalculatedBasedOnTriggerParametersAsync()
+        {
+            var expected = Prefix(Style.UML)
+                + Box(Style.UML, "A")
+                + Decision(Style.UML, "Decision1", "Function")
+                + Line("A", "Decision1", "X") + suffix;
+
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int>(Trigger.X);
+            sm.Configure(State.A)
+                .PermitDynamicAsync(trigger, i =>Task.FromResult(i == 1 ? State.B : State.C));
+
+            string dotGraph = UmlDotGraph.Format(sm.GetInfo());
+
 #if WRITE_DOTS_TO_FOLDER
             System.IO.File.WriteAllText(DestinationFolder + "DestinationStateIsCalculatedBasedOnTriggerParameters.dot", dotGraph);
 #endif
@@ -398,7 +441,7 @@ public void OnEntryWithTriggerParameter()
 
             Assert.Equal(expected, dotGraph);
         }
-        
+
         [Fact]
         public void SpacedUmlWithSubstate()
         {
@@ -408,14 +451,14 @@ public void SpacedUmlWithSubstate()
             string StateD = "State D";
             string TriggerX = "Trigger X";
             string TriggerY = "Trigger Y";
-            
+
             var expected = Prefix(Style.UML)
                            + Subgraph(Style.UML, StateD, $"{StateD}\\n----------\\nentry / Enter D",
                                Box(Style.UML, StateB)
                                + Box(Style.UML, StateC))
                            + Box(Style.UML, StateA, new List<string> { "Enter A" }, new List<string> { "Exit A" })
                            + Line(StateA, StateB, TriggerX) + Line(StateA, StateC, TriggerY)
-                           +  Environment.NewLine
+                           + Environment.NewLine
                            + $" init [label=\"\", shape=point];" + Environment.NewLine
                            + $" init -> \"{StateA}\"[style = \"solid\"]" + Environment.NewLine
                            + "}";
@@ -493,7 +536,36 @@ public void UmlWithDynamic()
             var sm = new StateMachine<State, Trigger>(State.A);
 
             sm.Configure(State.A)
-                .PermitDynamic(Trigger.X, DestinationSelector, null, new DynamicStateInfos { { State.B, "ChoseB"}, { State.C, "ChoseC" } });
+                .PermitDynamic(Trigger.X, DestinationSelector, null, new DynamicStateInfos { { State.B, "ChoseB" }, { State.C, "ChoseC" } });
+
+            sm.Configure(State.B);
+            sm.Configure(State.C);
+
+            string dotGraph = UmlDotGraph.Format(sm.GetInfo());
+#if WRITE_DOTS_TO_FOLDER
+            System.IO.File.WriteAllText(DestinationFolder + "UmlWithDynamic.dot", dotGraph);
+#endif
+
+            Assert.Equal(expected, dotGraph);
+        }
+
+        [Fact]
+        public void UmlWithDynamicAsync()
+        {
+            var expected = Prefix(Style.UML)
+                + Box(Style.UML, "A")
+                + Box(Style.UML, "B")
+                + Box(Style.UML, "C")
+                + Decision(Style.UML, "Decision1", "Function")
+                + Line("A", "Decision1", "X")
+                + Line("Decision1", "B", "X [ChoseB]")
+                + Line("Decision1", "C", "X [ChoseC]")
+                + suffix;
+
+            var sm = new StateMachine<State, Trigger>(State.A);
+
+            sm.Configure(State.A)
+                .PermitDynamicAsync(Trigger.X, () => Task.FromResult(DestinationSelector()), null, new DynamicStateInfos { { State.B, "ChoseB" }, { State.C, "ChoseC" } });
 
             sm.Configure(State.B);
             sm.Configure(State.C);
@@ -513,7 +585,7 @@ public void TransitionWithIgnoreAndEntry()
                 + Box(Style.UML, "A", new List<string> { "DoEntry" })
                 + Box(Style.UML, "B", new List<string> { "DoThisEntry" })
                 + Line("A", "B", "X")
-                + Line("A", "A", "Y") 
+                + Line("A", "A", "Y")
                 + Line("B", "B", "Z / DoThisEntry")
                 + suffix;
 

test/Stateless.Tests/DynamicAsyncTriggerBehaviourAsyncFixture.cs

@@ -0,0 +1,168 @@
+using System;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Stateless.Tests
+{
+    public class DynamicAsyncTriggerBehaviourAsyncFixture
+    {
+        [Fact]
+        public async Task PermitDynamic_Selects_Expected_State_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            sm.Configure(State.A)
+                .PermitDynamicAsync(Trigger.X, async () => { await Task.Delay(100); return State.B; });
+
+            await sm.FireAsync(Trigger.X);
+
+            Assert.Equal(State.B, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamic_With_TriggerParameter_Selects_Expected_State_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int>(Trigger.X);
+            sm.Configure(State.A)
+                .PermitDynamicAsync(trigger, async (i) => { await Task.Delay(100); return i == 1 ? State.B : State.C; });
+
+            await sm.FireAsync(trigger, 1);
+
+            Assert.Equal(State.B, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamic_Permits_Reentry_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var onExitInvoked = false;
+            var onEntryInvoked = false;
+            var onEntryFromInvoked = false;
+            sm.Configure(State.A)
+                .PermitDynamicAsync(Trigger.X, async () => { await Task.Delay(100); return State.A; })
+                .OnEntry(() => onEntryInvoked = true)
+                .OnEntryFrom(Trigger.X, () => onEntryFromInvoked = true)
+                .OnExit(() => onExitInvoked = true);
+
+            await sm.FireAsync(Trigger.X);
+
+            Assert.True(onExitInvoked, "Expected OnExit to be invoked");
+            Assert.True(onEntryInvoked, "Expected OnEntry to be invoked");
+            Assert.True(onEntryFromInvoked, "Expected OnEntryFrom to be invoked");
+            Assert.Equal(State.A, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamic_Selects_Expected_State_Based_On_DestinationStateSelector_Function_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var value = 'C';
+            sm.Configure(State.A)
+                .PermitDynamicAsync(Trigger.X, async () => { await Task.Delay(100); return value == 'B' ? State.B : State.C; });
+
+            await sm.FireAsync(Trigger.X);
+
+            Assert.Equal(State.C, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_With_TriggerParameter_Permits_Transition_When_GuardCondition_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int>(Trigger.X);
+            sm.Configure(State.A)
+                .PermitDynamicIfAsync(trigger, async (i) =>{ await Task.Delay(100); return i == 1 ? State.C : State.B; }, (i) => i == 1);
+
+            await sm.FireAsync(trigger, 1);
+
+            Assert.Equal(State.C, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_With_2_TriggerParameters_Permits_Transition_When_GuardCondition_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int, int>(Trigger.X);
+            sm.Configure(State.A).PermitDynamicIfAsync(
+                trigger,
+              async  (i, j) => { await Task.Yield(); return i == 1 && j == 2 ? State.C : State.B; },
+                (i, j) => i == 1 && j == 2);
+
+            await sm.FireAsync(trigger, 1, 2);
+
+            Assert.Equal(State.C, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_With_3_TriggerParameters_Permits_Transition_When_GuardCondition_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int, int, int>(Trigger.X);
+            sm.Configure(State.A).PermitDynamicIfAsync(
+                trigger,
+                async (i, j, k) => { await Task.Delay(100); return i == 1 && j == 2 && k == 3 ? State.C : State.B; },
+                (i, j, k) => i == 1 && j == 2 && k == 3);
+
+            await sm.FireAsync(trigger, 1, 2, 3);
+
+            Assert.Equal(State.C, sm.State);
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_With_TriggerParameter_Throws_When_GuardCondition_Not_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int>(Trigger.X);
+            sm.Configure(State.A)
+                .PermitDynamicIfAsync(trigger, async (i) => { await Task.Delay(100); return i > 0 ? State.C : State.B; }, guard: (i) => i == 2);
+
+            await Assert.ThrowsAsync<InvalidOperationException>(async () => await sm.FireAsync(trigger, 1));
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_With_2_TriggerParameters_Throws_When_GuardCondition_Not_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int, int>(Trigger.X);
+            sm.Configure(State.A).PermitDynamicIfAsync(
+                trigger,
+                async (i, j) => { await Task.Delay(100); return i > 0 ? State.C : State.B; },
+                (i, j) => i == 2 && j == 3);
+
+            await Assert.ThrowsAsync<InvalidOperationException>(async () => await sm.FireAsync(trigger, 1, 2));
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_With_3_TriggerParameters_Throws_When_GuardCondition_Not_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var trigger = sm.SetTriggerParameters<int, int, int>(Trigger.X);
+            sm.Configure(State.A).PermitDynamicIfAsync(trigger,
+                async (i, j, k) => { await Task.Delay(100); return i > 0 ? State.C : State.B; },
+                (i, j, k) => i == 2 && j == 3 && k == 4);
+
+            await Assert.ThrowsAsync<InvalidOperationException>(async () => await sm.FireAsync(trigger, 1, 2, 3));
+        }
+
+        [Fact]
+        public async Task PermitDynamicIf_Permits_Reentry_When_GuardCondition_Met_Async()
+        {
+            var sm = new StateMachine<State, Trigger>(State.A);
+            var onExitInvoked = false;
+            var onEntryInvoked = false;
+            var onEntryFromInvoked = false;
+            sm.Configure(State.A)
+                .PermitDynamicIfAsync(Trigger.X, async () =>{ await Task.Delay(100); return State.A; }, () => true)
+                .OnEntry(() => onEntryInvoked = true)
+                .OnEntryFrom(Trigger.X, () => onEntryFromInvoked = true)
+                .OnExit(() => onExitInvoked = true);
+
+            await sm.FireAsync(Trigger.X);
+
+            Assert.True(onExitInvoked, "Expected OnExit to be invoked");
+            Assert.True(onEntryInvoked, "Expected OnEntry to be invoked");
+            Assert.True(onEntryFromInvoked, "Expected OnEntryFrom to be invoked");
+            Assert.Equal(State.A, sm.State);
+        }
+    }
+}