refactor: add game listener

include/game/BaseGame.h

@@ -12,11 +12,25 @@ enum class GameState : std::uint8_t {
     Game,
     EndGame,
     Disconnected,
+    Closed
 };
 
 typedef std::map<std::uint8_t, Player> PlayerList;
 
-class Game {
+class GameListener {
+public:
+    virtual void OnPlayerJoin(PlayerID player) {}
+    virtual void OnPlayerLeave(PlayerID player) {}
+
+    virtual void OnGameStateUpdate(GameState newState) {}
+    virtual void OnGameBegin() {}
+    virtual void OnGameEnd() {}
+    virtual void OnGameClose() {}
+};
+
+typedef utils::ObjectNotifier<GameListener> GameNotifier;
+
+class Game : public GameNotifier {
 protected:
     World* m_World;
     TeamList m_Teams = { Team{TeamColor::Red}, Team{TeamColor::Blue} };