#nullable enable

using System;
using System.Threading;
using EntJoy.ECS;
using EntJoy.JobSystem;
using Godot;
using ShrinkSDK.Godot;

namespace ShrinkSDK.EntJoy.Godot;

/// <summary>Godot node that owns an EntJoy World and advances its frame boundary.</summary>
public partial class ShrinkEntJoyHost : ShrinkGodotHost
{
    private static readonly object SchedulerGate = new();
    private static int SchedulerUsers;
    private bool _schedulerAcquired;
    private bool _worldDisposed;
    private ulong _lastFrame = ulong.MaxValue;
    private SceneTree? _tree;

    [Export] public string EntJoyWorldName { get; set; } = "GodotWorld";

    public World? EntJoyWorld { get; private set; }

    public override void _Ready()
    {
        base._Ready();
        AcquireScheduler();
        EntJoyWorld = new World(EntJoyWorldName);
        World.DefaultWorld = EntJoyWorld;
        _tree = GetTree();
        _tree.ProcessFrame += OnProcessFrame;
        TreeExited += OnTreeExited;
    }

    public override void _Process(double delta)
    {
        base._Process(delta);
        Advance();
    }

    private void OnProcessFrame() => Advance();

    private void Advance()
    {
        if (EntJoyWorld == null || _worldDisposed) return;
        var frame = Engine.GetProcessFrames();
        if (frame == _lastFrame) return;
        _lastFrame = frame;
        EntJoyWorld.NextFrameEvents();
        NativeJobScheduler.EndFrame();
        EntJoyWorld.CurrentFrame++;
    }

    public override void _ExitTree()
    {
        DisposeWorld();
        base._ExitTree();
    }

    private void OnTreeExited()
    {
        if (_tree != null)
            _tree.ProcessFrame -= OnProcessFrame;
        _tree = null;
        TreeExited -= OnTreeExited;
        DisposeWorld();
    }

    private void AcquireScheduler()
    {
        lock (SchedulerGate)
        {
            if (SchedulerUsers++ == 0)
                NativeJobScheduler.Initialize();
            _schedulerAcquired = true;
        }
    }

    private void DisposeWorld()
    {
        if (_worldDisposed) return;
        _worldDisposed = true;
        EntJoyWorld?.Dispose();
        EntJoyWorld = null;

        if (!_schedulerAcquired) return;
        lock (SchedulerGate)
        {
            _schedulerAcquired = false;
            if (--SchedulerUsers == 0)
                NativeJobScheduler.Shutdown();
        }
    }
}