create IWantToJoinTheGameCommand

src/main/kotlin/eventDemo/app/command/GameCommandHandler.kt

@@ -2,6 +2,7 @@ package eventDemo.app.command
 
 import eventDemo.app.GameState
 import eventDemo.app.command.command.GameCommand
+import eventDemo.app.command.command.IWantToJoinTheGameCommand
 import eventDemo.app.command.command.IWantToPlayCardCommand
 import eventDemo.app.command.command.IamReadyToPlayCommand
 import eventDemo.app.entity.Player
@@ -42,13 +43,9 @@ class GameCommandHandler(
                 val gameState = command.buildGameState()
 
                 when (command) {
-                    is IWantToPlayCardCommand -> {
-                        command.run(gameState, playerNotifier, eventStream)
-                    }
-
-                    is IamReadyToPlayCommand -> {
-                        command.run(gameState, playerNotifier, eventStream)
-                    }
+                    is IWantToPlayCardCommand -> command.run(gameState, playerNotifier, eventStream)
+                    is IamReadyToPlayCommand -> command.run(gameState, playerNotifier, eventStream)
+                    is IWantToJoinTheGameCommand -> command.run(gameState, playerNotifier, eventStream)
                 }
             }
         }

src/main/kotlin/eventDemo/app/command/command/IWantToJoinTheGameCommand.kt

@@ -0,0 +1,44 @@
+package eventDemo.app.command.command
+
+import eventDemo.app.GameState
+import eventDemo.app.entity.GameId
+import eventDemo.app.entity.Player
+import eventDemo.app.event.GameEventStream
+import eventDemo.app.event.event.NewPlayerEvent
+import eventDemo.libs.command.CommandId
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * A command to perform an action to play a new card
+ */
+@Serializable
+@SerialName("JoinGame")
+data class IWantToJoinTheGameCommand(
+    override val payload: Payload,
+) : GameCommand {
+    override val id: CommandId = CommandId()
+
+    @Serializable
+    data class Payload(
+        override val gameId: GameId,
+        override val player: Player,
+    ) : GameCommand.Payload
+
+    fun run(
+        state: GameState,
+        playerNotifier: (String) -> Unit,
+        eventStream: GameEventStream,
+    ) {
+        if (!state.isStarted) {
+            eventStream.publish(
+                NewPlayerEvent(
+                    payload.gameId,
+                    payload.player,
+                ),
+            )
+        } else {
+            playerNotifier("The game is already started")
+        }
+    }
+}