create bus and subscriber

src/main/kotlin/eventDemo/app/actions/GameEventReactionSubscriber.kt

@@ -0,0 +1,27 @@
+package eventDemo.app.actions
+
+import eventDemo.libs.event.EventBus
+import eventDemo.libs.event.EventStream
+import eventDemo.shared.GameId
+import eventDemo.shared.event.GameEvent
+import eventDemo.shared.event.GameStartedEvent
+import eventDemo.shared.event.buildStateFromEventStream
+
+class GameEventReactionSubscriber(
+    private val eventBus: EventBus<GameEvent, GameId>,
+    private val eventStream: EventStream<GameEvent, GameId>,
+) {
+    fun init() {
+        eventBus.subscribe { event: GameEvent ->
+            val state = event.id.buildStateFromEventStream(eventStream)
+            if (state.isReady) {
+                eventStream.publish(
+                    GameStartedEvent.new(
+                        state.gameId,
+                        state.players,
+                    ),
+                )
+            }
+        }
+    }
+}