refactor: implement singleton pattern for key managers and improve resource access

scripts/UI/MainMenu.cs

@@ -1,5 +1,4 @@
 using Godot;
-using Mr.BrickAdventures;
 using Mr.BrickAdventures.Autoloads;
 
 namespace Mr.BrickAdventures.scripts.UI;
@@ -16,15 +15,12 @@ public partial class MainMenu : Control
     [Export] public Control SettingsControl { get; set; }
     [Export] public Control CreditsControl { get; set; }
 
-    private SaveSystem _saveSystem;
-    private GameManager _gameManager;
-    private UIManager _uiManager;
+    private SaveSystem SaveSystem => SaveSystem.Instance;
+    private GameManager GameManager => GameManager.Instance;
+    private UIManager UIManager => UIManager.Instance;
 
     public override void _Ready()
     {
-        _saveSystem = SaveSystem.Instance;
-        _gameManager = GameManager.Instance;
-        _uiManager = GetNode<UIManager>(Constants.UIManagerPath);
 
         NewGameButton.Pressed += OnNewGamePressed;
         ContinueButton.Pressed += OnContinuePressed;
@@ -33,9 +29,9 @@ public partial class MainMenu : Control
         ExitButton.Pressed += OnExitPressed;
 
         VersionLabel.Text = $"v. {ProjectSettings.GetSetting("application/config/version")}";
-        ContinueButton.Disabled = !_saveSystem.CheckSaveExists();
+        ContinueButton.Disabled = !SaveSystem.CheckSaveExists();
 
-        if (_saveSystem.CheckSaveExists())
+        if (SaveSystem.CheckSaveExists())
             ContinueButton.GrabFocus();
         else
             NewGameButton.GrabFocus();
@@ -43,26 +39,26 @@ public partial class MainMenu : Control
 
     private void OnExitPressed()
     {
-        _gameManager.QuitGame();
+        GameManager.QuitGame();
     }
 
     private void OnCreditsPressed()
     {
-        _uiManager.PushScreen(CreditsControl);
+        UIManager.PushScreen(CreditsControl);
     }
 
     private void OnSettingsPressed()
     {
-        _uiManager.PushScreen(SettingsControl);
+        UIManager.PushScreen(SettingsControl);
     }
 
     private void OnContinuePressed()
     {
-        _gameManager.ContinueGame();
+        GameManager.ContinueGame();
     }
 
     private void OnNewGamePressed()
     {
-        _gameManager.StartNewGame();
+        GameManager.StartNewGame();
     }
 }