From 7bf72f0b651ea66239883819b34d36b689cc524f Mon Sep 17 00:00:00 2001
From: infiniteyak <79123303+infiniteyak@users.noreply.github.com>
Date: Thu, 29 Dec 2022 00:29:07 -0800
Subject: [PATCH] Adding functionality to unsubscribe from events. (#95)

---
 features/events/events.go       | 25 ++++++++++++++++++++++++-
 features/events/example_test.go | 30 ++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/features/events/events.go b/features/events/events.go
index 17c325b..d25ca6b 100644
--- a/features/events/events.go
+++ b/features/events/events.go
@@ -60,7 +60,7 @@ func NewEventType[T any]() *EventType[T] {
 	return e
 }
 
-// RegisterHandler registers a subscriber for the event.
+// Subscribe registers a subscriber for the event.
 func (e *EventType[T]) Subscribe(w donburi.World, subscriber Subscriber[T]) {
 	if e.eventBusQuery.Count(w) == 0 {
 		entity := w.Entry(w.Create(e.eventBus, eventType))
@@ -77,6 +77,29 @@ func (e *EventType[T]) Subscribe(w donburi.World, subscriber Subscriber[T]) {
 	eventBus.subscribers = append(eventBus.subscribers, subscriber)
 }
 
+// Find the index of a subscriber
+func (e *EventType[T]) findSubscriber(w donburi.World, subscriber Subscriber[T]) (int, bool) {
+    if e.eventBusQuery.Count(w) != 0 {
+        eventBus := e.mustFindEventBus(w)
+        for i, s := range eventBus.subscribers {
+            if reflect.ValueOf(s).Pointer() == reflect.ValueOf(subscriber).Pointer() {
+                return i, true
+            }
+        }
+    }
+    return 0, false
+}
+
+// Unsubscribe removes a subscriber for the event.
+func (e *EventType[T]) Unsubscribe(w donburi.World, subscriber Subscriber[T]) {
+    index, found := e.findSubscriber(w, subscriber)
+    if found {
+        eventBus := e.mustFindEventBus(w)
+        eventBus.subscribers[index] = eventBus.subscribers[len(eventBus.subscribers)-1]
+        eventBus.subscribers = eventBus.subscribers[:len(eventBus.subscribers)-1]
+    }
+}
+
 // Publish publishes an event.
 func (e *EventType[T]) Publish(w donburi.World, event T) {
 	eventBus := e.mustFindEventBus(w)
diff --git a/features/events/example_test.go b/features/events/example_test.go
index 9abcd54..231bc40 100644
--- a/features/events/example_test.go
+++ b/features/events/example_test.go
@@ -40,6 +40,36 @@ func TestEvents(t *testing.T) {
 	}
 }
 
+func TestUnsubscribe(t *testing.T) {
+
+	w := donburi.NewWorld()
+
+	EnemyKilledEvent.Subscribe(w, HandleEnemyKilled)
+	EnemyKilledEvent.Publish(w, &EnemyKilled{EnemyID: 1})
+
+	events.ProcessAllEvents(w)
+
+	ev := lastReceivedEvent
+
+	if ev == nil {
+		t.Errorf("event should be received")
+	}
+
+	if ev.EnemyID != 1 {
+		t.Errorf("event should have value 1")
+	}
+
+	lastReceivedEvent = nil
+	EnemyKilledEvent.Unsubscribe(w, HandleEnemyKilled)
+	EnemyKilledEvent.Publish(w, &EnemyKilled{EnemyID: 1})
+
+	events.ProcessAllEvents(w)
+
+	if lastReceivedEvent != nil {
+		t.Errorf("event should not be received")
+	}
+}
+
 var (
 	lastReceivedEvent *EnemyKilled = nil
 )