Create GameStateRepository

Use GameState.apply() to build Projection
Create GameEventHandler
Add PlayerWinEvent

src/main/kotlin/eventDemo/app/event/projection/GameStateRepository.kt

@@ -0,0 +1,34 @@
+package eventDemo.app.event.projection
+
+import eventDemo.app.entity.GameId
+import eventDemo.app.event.GameEventHandler
+import eventDemo.app.event.GameEventStream
+import java.util.concurrent.ConcurrentHashMap
+
+class GameStateRepository(
+    private val eventStream: GameEventStream,
+    eventHandler: GameEventHandler,
+) {
+    private val projections: ConcurrentHashMap<GameId, GameState> = ConcurrentHashMap()
+
+    init {
+        eventHandler.registerProjectionBuilder { event ->
+            val projection = projections[event.gameId]
+            if (projection == null) {
+                event.gameId
+                    .buildStateFromEventStream(eventStream)
+                    .update()
+            } else {
+                projection
+                    .apply(event)
+                    .let { projections.put(it.gameId, it) }
+            }
+        }
+    }
+
+    fun get(gameId: GameId): GameState = gameId.buildStateFromEventStream(eventStream)
+
+    private fun GameState.update() {
+        projections[gameId] = this
+    }
+}