cirnogodot/Scripts/GlobalState.cs

using Cirno.Scripts.Resources;
using Godot;

public partial class GlobalState : Node
{
    public static GlobalState Instance { get; private set; }

    public Node CurrentScene { get; set; }

    public override void _Ready()
    {
        Instance = this;

        Viewport root = GetTree().Root;
        // Using a negative index counts from the end, so this gets the last child node of `root`.
        CurrentScene = root.GetChild(-1);
    }

    public void GotoScene(string path)
    {
        // This function will usually be called from a signal callback,
        // or some other function from the current scene.
        // Deleting the current scene at this point is
        // a bad idea, because it may still be executing code.
        // This will result in a crash or unexpected behavior.

        // The solution is to defer the load to a later time, when
        // we can be sure that no code from the current scene is running:

        CallDeferred(MethodName.DeferredGotoScene, path, new MapStartDataResource());
    }

    public void GoToScene(string path, MapStartDataResource startData)
    {
        // TODO: Implement startdata usage
        CallDeferred(MethodName.DeferredGotoScene, path, startData);
    }

    private void DeferredGotoScene(string path, MapStartDataResource startData = null)
    {
        // It is now safe to remove the current scene.
        CurrentScene.Free();

        // Load a new scene.
        var nextScene = GD.Load<PackedScene>(path);

        // Instance the new scene.
        CurrentScene = nextScene.Instantiate();

        // Add it to the active scene, as child of root.
        GetTree().Root.AddChild(CurrentScene);

        // Optionally, to make it compatible with the SceneTree.change_scene_to_file() API.
        GetTree().CurrentScene = CurrentScene;
        
        // // Update current scene here too
        // CurrentScene = GetTree().Root.GetChild(-1);
        
        if (startData is not null)
        {
            // Call deferred if it gives issues
            DeferredAddStartDataToGameManager(startData);
        }
    }

    private void DeferredAddStartDataToGameManager(MapStartDataResource resource)
    {
        GameManager.Instance.ApplyMapStartData(resource);
    }
}