#nullable enable

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Reflection;
using System.Threading;
using System.Threading.Tasks;
using Cysharp.Threading.Tasks;
using Godot;
using ShrinkApp;
using ShrinkDataSaver;
using ShrinkEventBus;
using ShrinkNetwork;
using ShrinkSDK.Runtime;

namespace ShrinkSDK.Godot;

public sealed class ShrinkGodotRuntime : IShrinkMainThreadDispatcher, IShrinkDeferredMainThreadDispatcher,
    IShrinkLogger, IShrinkClock, IShrinkPathProvider, IShrinkScreenshotProvider,
    IShrinkApplicationLifecycle
{
    private readonly ConcurrentQueue<Action> _dispatchQueue = new();
    private readonly Dictionary<ShrinkNetworkService, ShrinkNetworkDispatchQueue> _networkServices = new();
    private readonly object _dispatchGate = new();
    private KeyValuePair<ShrinkNetworkService, ShrinkNetworkDispatchQueue>[] _networkSnapshot = [];
    private readonly SemaphoreSlim _lifecycleGate = new(1, 1);
    private Node? _owner;
    private int _mainThreadId;
    private volatile bool _initialized;
    private volatile bool _shutdown;
    private bool _networkPumpRunning;
    private ShrinkAppRuntime? _appRuntime;

    public event Action? Paused;
    public event Action? Resumed;
    public event Action? Exiting;

    public int DispatchBudgetPerFrame { get; set; } = 256;
    public int NetworkDispatchBudgetPerFrame { get; set; } = 256;

    public bool IsInitialized => _initialized;
    public bool IsShutdown => _shutdown;
    public bool IsMainThread => Thread.CurrentThread.ManagedThreadId == _mainThreadId;
    public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;
    public double UnscaledTimeSeconds => Time.GetTicksMsec() / 1000d;
    public string PersistentDataPath => ProjectSettings.GlobalizePath("user://");
    public string TemporaryDataPath => OS.GetCacheDir();

    public void Initialize(Node owner)
    {
        if (owner == null)
            throw new ArgumentNullException(nameof(owner));
        if (_shutdown)
            throw new InvalidOperationException("ShrinkGodotRuntime has already shut down.");
        if (_initialized)
        {
            if (!ReferenceEquals(_owner, owner))
                throw new InvalidOperationException("ShrinkGodotRuntime is already bound to another owner.");
            return;
        }

        _owner = owner;
        _mainThreadId = Thread.CurrentThread.ManagedThreadId;
        ShrinkRuntimeServices.Configure(this, this, this, this, this, this);
        ShrinkEventBusRuntime.ConfigureMainThreadDispatcher(this);
        ShrinkDataSaverPlatform.Configure(this, this, this, this);
        _initialized = true;
    }

    public void Tick(double delta)
    {
        if (!_initialized || _shutdown) return;
        RequireMainThread();

        var budget = Math.Max(1, DispatchBudgetPerFrame);
        var count = Math.Min(budget, _dispatchQueue.Count);
        while (count-- > 0 && _dispatchQueue.TryDequeue(out var action))
        {
            try
            {
                action();
            }
            catch (Exception exception)
            {
                Log(ShrinkLogLevel.Error, "Godot dispatch callback failed.", exception);
            }
        }

        PumpNetworkAsync().Forget();
    }

    public void Notify(int what)
    {
        if (_shutdown)
            return;
        switch ((long)what)
        {
            case MainLoop.NotificationApplicationPaused:
            case MainLoop.NotificationApplicationFocusOut:
                Paused?.Invoke();
                break;
            case MainLoop.NotificationApplicationResumed:
            case MainLoop.NotificationApplicationFocusIn:
                Resumed?.Invoke();
                break;
            case Node.NotificationWMCloseRequest:
            case Node.NotificationPredelete:
                Exiting?.Invoke();
                break;
        }
    }

    public async UniTask<ShrinkAppRuntime> StartAppAsync(ShrinkAppSettings? settings = null,
        ShrinkAppServices? services = null)
    {
        await _lifecycleGate.WaitAsync();
        try
        {
            if (!_initialized)
                throw new InvalidOperationException("Initialize the Godot runtime before starting the app.");
            if (_shutdown)
                throw new InvalidOperationException("ShrinkGodotRuntime has already shut down.");
            if (_appRuntime?.IsRunning == true)
                return _appRuntime;
            if (_appRuntime != null)
            {
                await _appRuntime.ShutdownAsync();
                _appRuntime = null;
            }

            _appRuntime = new ShrinkAppRuntime(_owner, settings, services);
            await _appRuntime.StartAsync();
            return _appRuntime;
        }
        finally
        {
            _lifecycleGate.Release();
        }
    }

    public async UniTask ShutdownAsync()
    {
        await _lifecycleGate.WaitAsync();
        try
        {
            if (_shutdown)
                return;
            var appRuntime = _appRuntime;
            _appRuntime = null;
            try
            {
                if (appRuntime != null)
                    await appRuntime.ShutdownAsync();
            }
            finally
            {
                lock (_dispatchGate)
                {
                    _shutdown = true;
                    while (_dispatchQueue.TryDequeue(out _)) { }
                }

                foreach (var pair in _networkServices)
                {
                    pair.Key.DispatchScheduler = ShrinkNetworkDispatchSchedulers.Inline;
                    pair.Value.Dispose();
                }
                _networkServices.Clear();
                _networkSnapshot = [];
            }
        }
        finally
        {
            _lifecycleGate.Release();
        }
    }

    public async UniTask StopAppAsync()
    {
        await _lifecycleGate.WaitAsync();
        try
        {
            if (_shutdown || _appRuntime == null)
                return;
            var appRuntime = _appRuntime;
            _appRuntime = null;
            await appRuntime.ShutdownAsync();
        }
        finally
        {
            _lifecycleGate.Release();
        }
    }

    public bool TryPost(Action action)
    {
        if (action == null)
            throw new ArgumentNullException(nameof(action));
        lock (_dispatchGate)
        {
            if (!_initialized || _shutdown) return false;
            _dispatchQueue.Enqueue(action);
            return true;
        }
    }

    public bool TryPostDeferred(Action action) => TryPost(action);

    public bool AddNetworkService(ShrinkNetworkService service)
    {
        if (service == null)
            throw new ArgumentNullException(nameof(service));
        if (!_initialized || _shutdown) return false;
        RequireMainThread();
        if (_networkServices.ContainsKey(service))
            return true;
        var queue = new ShrinkNetworkDispatchQueue(Math.Max(1, NetworkDispatchBudgetPerFrame * 4));
        service.DispatchScheduler = queue;
        _networkServices.Add(service, queue);
        UpdateNetworkSnapshot();
        return true;
    }

    public bool RemoveNetworkService(ShrinkNetworkService service)
    {
        if (service == null)
            throw new ArgumentNullException(nameof(service));
        RequireMainThread();
        if (!_networkServices.Remove(service, out var queue))
            return false;
        service.DispatchScheduler = ShrinkNetworkDispatchSchedulers.Inline;
        queue.Dispose();
        UpdateNetworkSnapshot();
        return true;
    }

    public static ShrinkCodeGenWovenAttribute RequireWoven(Assembly assembly)
    {
        if (assembly == null)
            throw new ArgumentNullException(nameof(assembly));
        return assembly.GetCustomAttribute<ShrinkCodeGenWovenAttribute>() ??
               throw new InvalidOperationException(
                   $"Assembly '{assembly.GetName().Name}' was not woven by ShrinkSDK.CodeGen. Ensure the package is installed and ShrinkCodeGenEnabled is not false.");
    }

    public void Log(ShrinkLogLevel level, string message, Exception? exception = null)
    {
        var text = exception == null ? message : $"{message}{System.Environment.NewLine}{exception}";
        if (level >= ShrinkLogLevel.Error)
            GD.PushError(text);
        else if (level >= ShrinkLogLevel.Warning)
            GD.PushWarning(text);
        else
            GD.Print(text);
    }

    public ValueTask<byte[]> CapturePngAsync(CancellationToken cancellationToken = default)
    {
        cancellationToken.ThrowIfCancellationRequested();
        if (_owner == null || !GodotObject.IsInstanceValid(_owner))
            throw new InvalidOperationException("ShrinkGodotRuntime has no valid owner viewport.");
        var image = _owner.GetViewport().GetTexture().GetImage();
        return ValueTask.FromResult(image.SavePngToBuffer());
    }

    private void RequireMainThread()
    {
        if (!IsMainThread) throw new InvalidOperationException("Godot lifecycle and network registration require the owner thread.");
    }

    private void UpdateNetworkSnapshot()
    {
        _networkSnapshot = new KeyValuePair<ShrinkNetworkService, ShrinkNetworkDispatchQueue>[_networkServices.Count];
        ((ICollection<KeyValuePair<ShrinkNetworkService, ShrinkNetworkDispatchQueue>>)_networkServices).CopyTo(_networkSnapshot, 0);
    }

    private async UniTaskVoid PumpNetworkAsync()
    {
        if (_networkPumpRunning || _shutdown)
            return;
        _networkPumpRunning = true;
        try
        {
            foreach (var pair in _networkSnapshot)
            {
                if (_shutdown) break;
                if (_networkServices.TryGetValue(pair.Key, out var queue) && ReferenceEquals(queue, pair.Value))
                    await queue.PumpAsync(Math.Max(1, NetworkDispatchBudgetPerFrame));
            }
        }
        finally
        {
            _networkPumpRunning = false;
        }
    }
}