feat: add OnExitFrom configuration method (closes #75)

config.go

@@ -160,6 +160,16 @@ func (sc *StateConfiguration) OnExit(action ActionFunc) *StateConfiguration {
 	return sc
 }
 
+// OnExitWith specifies an action that will execute when transitioning from the configured state with a specific trigger.
+func (sc *StateConfiguration) OnExitWith(trigger Trigger, action ActionFunc) *StateConfiguration {
+	sc.sr.ExitActions = append(sc.sr.ExitActions, actionBehaviour{
+		Action:      action,
+		Description: newinvocationInfo(action),
+		Trigger:     &trigger,
+	})
+	return sc
+}
+
 // SubstateOf sets the superstate that the configured state is a substate of.
 // Substates inherit the allowed transitions of their superstate.
 // When entering directly into a substate from outside of the superstate,

example_test.go

@@ -66,6 +66,10 @@ func Example() {
 
 	phoneCall.Configure(stateOnHold).
 		SubstateOf(stateConnected).
+		OnExitWith(triggerPhoneHurledAgainstWall, func(ctx context.Context, args ...any) error {
+			onWasted()
+			return nil
+		}).
 		Permit(triggerTakenOffHold, stateConnected).
 		Permit(triggerPhoneHurledAgainstWall, statePhoneDestroyed)
 
@@ -90,6 +94,7 @@ func Example() {
 	// Microphone muted!
 	// Microphone unmuted!
 	// Volume set to 11!
+	// Wasted!
 	// [Timer:] Call ended at 11:30am
 	// State is PhoneDestroyed
 
@@ -111,6 +116,10 @@ func onDialed(callee string) {
 	fmt.Printf("[Phone Call] placed for : [%s]\n", callee)
 }
 
+func onWasted() {
+	fmt.Println("Wasted!")
+}
+
 func startCallTimer(_ context.Context, _ ...any) error {
 	fmt.Println("[Timer:] Call started at 11:00am")
 	return nil

graph_test.go

@@ -112,6 +112,10 @@ func phoneCall() *stateless.StateMachine {
 
 	phoneCall.Configure(stateOnHold).
 		SubstateOf(stateConnected).
+		OnExitWith(triggerPhoneHurledAgainstWall, func(ctx context.Context, args ...any) error {
+			onWasted()
+			return nil
+		}).
 		Permit(triggerTakenOffHold, stateConnected).
 		Permit(triggerPhoneHurledAgainstWall, statePhoneDestroyed)
 

statemachine_test.go

@@ -368,6 +368,31 @@ func TestStateMachine_Fire_ParametersSuppliedToFireArePassedToEntryAction(t *tes
 	}
 }
 
+func TestStateMachine_Fire_ParametersSuppliedToFireArePassedToExitAction(t *testing.T) {
+	sm := NewStateMachine(stateB)
+	sm.SetTriggerParameters(triggerX, reflect.TypeOf(""), reflect.TypeOf(0))
+	sm.Configure(stateB).Permit(triggerX, stateC)
+
+	var (
+		entryArg1 string
+		entryArg2 int
+	)
+	sm.Configure(stateB).OnExitWith(triggerX, func(_ context.Context, args ...any) error {
+		entryArg1 = args[0].(string)
+		entryArg2 = args[1].(int)
+		return nil
+	})
+	suppliedArg1, suppliedArg2 := "something", 2
+	sm.Fire(triggerX, suppliedArg1, suppliedArg2)
+
+	if entryArg1 != suppliedArg1 {
+		t.Errorf("entryArg1 = %v, want %v", entryArg1, suppliedArg1)
+	}
+	if entryArg2 != suppliedArg2 {
+		t.Errorf("entryArg2 = %v, want %v", entryArg2, suppliedArg2)
+	}
+}
+
 func TestStateMachine_OnUnhandledTrigger_TheProvidedHandlerIsCalledWithStateAndTrigger(t *testing.T) {
 	sm := NewStateMachine(stateB)
 	var (
@@ -570,6 +595,29 @@ func TestStateMachine_Fire_IgnoreVsPermitReentryFrom(t *testing.T) {
 	}
 }
 
+func TestStateMachine_Fire_IgnoreVsPermitReentryExitWith(t *testing.T) {
+	sm := NewStateMachine(stateA)
+	var calls int
+	sm.Configure(stateA).
+		OnExitWith(triggerX, func(_ context.Context, _ ...any) error {
+			calls += 1
+			return nil
+		}).
+		OnExitWith(triggerY, func(_ context.Context, _ ...any) error {
+			calls += 1
+			return nil
+		}).
+		PermitReentry(triggerX).
+		Ignore(triggerY)
+
+	sm.Fire(triggerX)
+	sm.Fire(triggerY)
+
+	if calls != 1 {
+		t.Errorf("calls = %d, want %d", calls, 1)
+	}
+}
+
 func TestStateMachine_Fire_IfSelfTransitionPermited_ActionsFire_InSubstate(t *testing.T) {
 	sm := NewStateMachine(stateA)
 	var onEntryStateBfired, onExitStateBfired, onExitStateAfired bool