using System;
using System.Collections.Generic;
using System.Threading;
using Cysharp.Threading.Tasks;
using UnityEngine;

namespace AlicizaX
{
    [Serializable]
    public sealed class GameObjectPoolInstanceSnapshot : IMemory
    {
        public string instanceName;
        public bool isActive;
        public float idleDuration;
        public GameObject gameObject;

        public void Clear()
        {
            instanceName = null;
            isActive = false;
            idleDuration = 0f;
            gameObject = null;
        }
    }

    [Serializable]
    public sealed class GameObjectPoolSnapshot : IMemory
    {
        public string group;
        public string assetPath;
        public PoolMatchMode matchMode;
        public PoolResourceLoaderType loaderType;
        public int capacity;
        public int totalCount;
        public int activeCount;
        public int inactiveCount;
        public float instanceIdleTimeout;
        public float prefabUnloadDelay;
        public bool prefabLoaded;
        public float prefabIdleDuration;
        public List<GameObjectPoolInstanceSnapshot> instances = new List<GameObjectPoolInstanceSnapshot>();

        public void Clear()
        {
            group = null;
            assetPath = null;
            matchMode = default;
            loaderType = default;
            capacity = 0;
            totalCount = 0;
            activeCount = 0;
            inactiveCount = 0;
            instanceIdleTimeout = 0f;
            prefabUnloadDelay = 0f;
            prefabLoaded = false;
            prefabIdleDuration = 0f;

            for (int i = 0; i < instances.Count; i++)
            {
                MemoryPool.Release(instances[i]);
            }

            instances.Clear();
        }
    }

    [DisallowMultipleComponent]
    public sealed class PooledGameObjectMarker : MonoBehaviour
    {
        private RuntimePrefabPool _owner;
        private RuntimePooledInstance _instance;

        internal void Bind(RuntimePrefabPool owner, RuntimePooledInstance instance)
        {
            _owner = owner;
            _instance = instance;
        }

        public void Detach()
        {
            _owner = null;
            _instance = null;
        }

        private void OnDestroy()
        {
            if (_owner != null && _instance != null)
            {
                _owner.NotifyInstanceDestroyed(_instance);
            }
        }
    }

    internal sealed class RuntimePooledInstance : IMemory
    {
        public GameObject GameObject { get; private set; }
        public PooledGameObjectMarker Marker { get; private set; }
        public LinkedListNode<RuntimePooledInstance> InactiveNode { get; set; }
        public bool IsActive { get; set; }
        public float LastReleaseTime { get; set; }

        public void Initialize(GameObject gameObject, PooledGameObjectMarker marker)
        {
            GameObject = gameObject;
            Marker = marker;
        }

        public void Clear()
        {
            GameObject = null;
            Marker = null;
            InactiveNode = null;
            IsActive = false;
            LastReleaseTime = 0f;
        }
    }

    internal sealed class RuntimePrefabPool : IMemory
    {
        private static readonly Comparison<GameObjectPoolInstanceSnapshot> InstanceSnapshotComparer = (left, right) =>
        {
            if (left == null && right == null) return 0;
            if (left == null) return 1;
            if (right == null) return -1;
            if (left.isActive != right.isActive) return left.isActive ? -1 : 1;
            return string.Compare(left.instanceName, right.instanceName, StringComparison.Ordinal);
        };
        private PoolConfig _config;
        private string _assetPath;
        private IResourceLoader _loader;
        private GameObjectPool _service;
        private CancellationToken _shutdownToken;
        private Dictionary<GameObject, RuntimePooledInstance> _instancesByObject;
        private LinkedList<RuntimePooledInstance> _inactiveInstances;
        private List<RuntimePooledInstance> _shutdownBuffer;
        private Transform _root;

        private GameObject _prefab;
        private UniTaskCompletionSource<GameObject> _prefabLoadSource;
        private int _activeCount;
        private float _lastPrefabTouchTime;

        public RuntimePrefabPool()
        {
            _instancesByObject = new Dictionary<GameObject, RuntimePooledInstance>();
            _inactiveInstances = new LinkedList<RuntimePooledInstance>();
            _shutdownBuffer = new List<RuntimePooledInstance>();
        }

        public void Initialize(
            PoolConfig config,
            string assetPath,
            IResourceLoader loader,
            GameObjectPool service,
            CancellationToken shutdownToken)
        {
            _config = config ?? throw new ArgumentNullException(nameof(config));
            _assetPath = assetPath ?? throw new ArgumentNullException(nameof(assetPath));
            _loader = loader ?? throw new ArgumentNullException(nameof(loader));
            _service = service ?? throw new ArgumentNullException(nameof(service));
            _shutdownToken = shutdownToken;
            _lastPrefabTouchTime = Time.time;

            _instancesByObject.Clear();
            _inactiveInstances.Clear();
            _prefab = null;
            _prefabLoadSource = null;
            _activeCount = 0;

            GameObject rootObject = new GameObject($"Pool_{SanitizeName(config.group)}_{SanitizeName(assetPath)}");
            _root = rootObject.transform;
            _root.SetParent(service.poolContainer, false);
            rootObject.SetActive(false);
        }

        public string AssetPath => _assetPath;
        public PoolConfig Config => _config;
        public int TotalCount => _instancesByObject.Count;
        public int ActiveCount => _activeCount;
        public int InactiveCount => _inactiveInstances.Count;
        public bool IsPrefabLoaded => _prefab != null;
        public float PrefabIdleDuration => _prefab == null ? 0f : Mathf.Max(0f, Time.time - _lastPrefabTouchTime);

        public GameObject Acquire(Transform parent)
        {
            EnsurePrefabLoaded();
            return AcquirePrepared(parent);
        }

        public async UniTask<GameObject> AcquireAsync(Transform parent, CancellationToken cancellationToken)
        {
            await EnsurePrefabLoadedAsync(cancellationToken);
            return AcquirePrepared(parent);
        }

        public void Warmup(int count)
        {
            if (count <= 0)
            {
                return;
            }

            EnsurePrefabLoaded();
            WarmupPrepared(count);
        }

        public async UniTask WarmupAsync(int count, CancellationToken cancellationToken)
        {
            if (count <= 0)
            {
                return;
            }

            await EnsurePrefabLoadedAsync(cancellationToken);
            WarmupPrepared(count);
        }

        public bool Release(GameObject gameObject)
        {
            if (gameObject == null || !_instancesByObject.TryGetValue(gameObject, out RuntimePooledInstance instance))
            {
                return false;
            }

            if (!instance.IsActive)
            {
                return true;
            }

            instance.IsActive = false;
            instance.LastReleaseTime = Time.time;
            _activeCount = Mathf.Max(0, _activeCount - 1);

            gameObject.SetActive(false);

            Transform transform = gameObject.transform;
            transform.SetParent(_root, false);
            transform.localPosition = Vector3.zero;
            transform.localRotation = Quaternion.identity;
            transform.localScale = Vector3.one;

            instance.InactiveNode = _inactiveInstances.AddLast(instance);
            TouchPrefab();
            return true;
        }

        public void NotifyInstanceDestroyed(RuntimePooledInstance instance)
        {
            if (instance == null)
            {
                return;
            }

            RemoveInstance(instance);
            MemoryPool.Release(instance);
        }

        public void TrimExpiredInstances(float now)
        {
            if (_config.instanceIdleTimeout > 0f)
            {
                while (_inactiveInstances.First != null)
                {
                    RuntimePooledInstance candidate = _inactiveInstances.First.Value;
                    if (now - candidate.LastReleaseTime < _config.instanceIdleTimeout)
                    {
                        break;
                    }

                    DestroyInstance(candidate);
                }
            }

            if (_prefab != null &&
                _instancesByObject.Count == 0 &&
                _config.prefabUnloadDelay > 0f &&
                now - _lastPrefabTouchTime >= _config.prefabUnloadDelay)
            {
                _loader.UnloadAsset(_prefab);
                _prefab = null;
            }
        }

        public GameObjectPoolSnapshot CreateSnapshot()
        {
            var snapshot = MemoryPool.Acquire<GameObjectPoolSnapshot>();
            snapshot.group = _config.group;
            snapshot.assetPath = _assetPath;
            snapshot.matchMode = _config.matchMode;
            snapshot.loaderType = _config.resourceLoaderType;
            snapshot.capacity = _config.capacity;
            snapshot.totalCount = _instancesByObject.Count;
            snapshot.activeCount = _activeCount;
            snapshot.inactiveCount = _inactiveInstances.Count;
            snapshot.instanceIdleTimeout = _config.instanceIdleTimeout;
            snapshot.prefabUnloadDelay = _config.prefabUnloadDelay;
            snapshot.prefabLoaded = _prefab != null;
            snapshot.prefabIdleDuration = PrefabIdleDuration;

            foreach (RuntimePooledInstance instance in _instancesByObject.Values)
            {
                var instanceSnapshot = MemoryPool.Acquire<GameObjectPoolInstanceSnapshot>();
                instanceSnapshot.instanceName = instance.GameObject != null ? instance.GameObject.name : "<destroyed>";
                instanceSnapshot.isActive = instance.IsActive;
                instanceSnapshot.idleDuration = instance.IsActive ? 0f : Mathf.Max(0f, Time.time - instance.LastReleaseTime);
                instanceSnapshot.gameObject = instance.GameObject;
                snapshot.instances.Add(instanceSnapshot);
            }

            snapshot.instances.Sort(InstanceSnapshotComparer);

            return snapshot;
        }

        public void Shutdown()
        {
            _shutdownBuffer.AddRange(_instancesByObject.Values);
            foreach (RuntimePooledInstance instance in _shutdownBuffer)
            {
                DestroyInstance(instance);
            }
            _shutdownBuffer.Clear();

            _inactiveInstances.Clear();
            _instancesByObject.Clear();
            _activeCount = 0;

            if (_prefab != null)
            {
                _loader.UnloadAsset(_prefab);
                _prefab = null;
            }

            if (_root != null)
            {
                GameObject.Destroy(_root.gameObject);
            }

            _root = null;
        }

        private void EnsurePrefabLoaded()
        {
            if (_prefab != null)
            {
                TouchPrefab();
                return;
            }

            if (_prefabLoadSource != null)
            {
                throw new InvalidOperationException(
                    $"Pool asset '{_assetPath}' is being loaded asynchronously. Use the async acquire API.");
            }

            _prefab = _loader.LoadPrefab(_assetPath);
            if (_prefab == null)
            {
                throw new InvalidOperationException($"Failed to load pooled prefab '{_assetPath}'.");
            }

            TouchPrefab();
        }

        private async UniTask EnsurePrefabLoadedAsync(CancellationToken cancellationToken)
        {
            if (_prefab != null)
            {
                TouchPrefab();
                return;
            }

            if (_prefabLoadSource != null)
            {
                await _prefabLoadSource.Task.AttachExternalCancellation(cancellationToken);
                return;
            }

            _prefabLoadSource = new UniTaskCompletionSource<GameObject>();

            try
            {
                GameObject prefab = await _loader.LoadPrefabAsync(_assetPath, _shutdownToken);
                if (prefab == null)
                {
                    throw new InvalidOperationException($"Failed to load pooled prefab '{_assetPath}'.");
                }

                _prefab = prefab;
                TouchPrefab();
                _prefabLoadSource.TrySetResult(prefab);
            }
            catch (Exception exception)
            {
                _prefabLoadSource.TrySetException(exception);
                throw;
            }
            finally
            {
                _prefabLoadSource = null;
            }
        }

        private void WarmupPrepared(int requestedCount)
        {
            int targetCount = Mathf.Clamp(requestedCount, 0, _config.capacity);
            if (targetCount <= _instancesByObject.Count)
            {
                return;
            }

            int toCreate = targetCount - _instancesByObject.Count;
            for (int i = 0; i < toCreate; i++)
            {
                RuntimePooledInstance instance = CreateInstance();
                ParkInactive(instance);
            }
        }

        private GameObject AcquirePrepared(Transform parent)
        {
            RuntimePooledInstance instance = null;

            if (_inactiveInstances.Last != null)
            {
                instance = _inactiveInstances.Last.Value;
                RemoveInactiveNode(instance);
            }
            else if (_instancesByObject.Count < _config.capacity)
            {
                instance = CreateInstance();
            }

            if (instance == null)
            {
                Log.Warning($"Pool exhausted for '{_assetPath}'. Capacity: {_config.capacity}");
                return null;
            }

            instance.IsActive = true;
            _activeCount++;
            TouchPrefab();

            GameObject gameObject = instance.GameObject;
            if (parent != null)
            {
                gameObject.transform.SetParent(parent, false);
            }

            gameObject.SetActive(true);
            return gameObject;
        }

        private RuntimePooledInstance CreateInstance()
        {
            GameObject gameObject = GameObject.Instantiate(_prefab);
            gameObject.SetActive(false);
            gameObject.transform.SetParent(_root, false);

            PooledGameObjectMarker marker = gameObject.GetComponent<PooledGameObjectMarker>();
            if (marker == null)
            {
                marker = gameObject.AddComponent<PooledGameObjectMarker>();
            }

            var instance = MemoryPool.Acquire<RuntimePooledInstance>();
            instance.Initialize(gameObject, marker);
            marker.Bind(this, instance);
            _instancesByObject.Add(gameObject, instance);
            _service.RegisterOwnedObject(gameObject, this);
            TouchPrefab();
            return instance;
        }

        private void ParkInactive(RuntimePooledInstance instance)
        {
            if (instance == null)
            {
                return;
            }

            instance.IsActive = false;
            instance.LastReleaseTime = Time.time;

            Transform transform = instance.GameObject.transform;
            transform.SetParent(_root, false);
            transform.localPosition = Vector3.zero;
            transform.localRotation = Quaternion.identity;
            transform.localScale = Vector3.one;
            instance.GameObject.SetActive(false);
            instance.InactiveNode = _inactiveInstances.AddLast(instance);
        }

        private void DestroyInstance(RuntimePooledInstance instance)
        {
            if (instance == null)
            {
                return;
            }

            RemoveInstance(instance);

            if (instance.GameObject != null)
            {
                instance.Marker?.Detach();
                GameObject.Destroy(instance.GameObject);
            }

            MemoryPool.Release(instance);
        }

        private void RemoveInstance(RuntimePooledInstance instance)
        {
            GameObject gameObject = instance?.GameObject;
            if (gameObject == null)
            {
                return;
            }

            RemoveInactiveNode(instance);

            if (instance.IsActive)
            {
                instance.IsActive = false;
                _activeCount = Mathf.Max(0, _activeCount - 1);
            }

            _instancesByObject.Remove(gameObject);
            _service.UnregisterOwnedObject(gameObject);
            TouchPrefab();
        }

        private void RemoveInactiveNode(RuntimePooledInstance instance)
        {
            if (instance?.InactiveNode == null)
            {
                return;
            }

            _inactiveInstances.Remove(instance.InactiveNode);
            instance.InactiveNode = null;
        }

        private void TouchPrefab()
        {
            _lastPrefabTouchTime = Time.time;
        }

        public void Clear()
        {
            _config = null;
            _assetPath = null;
            _loader = null;
            _service = null;
            _shutdownToken = default;
            _instancesByObject.Clear();
            _inactiveInstances.Clear();
            _shutdownBuffer.Clear();
            _root = null;
            _prefab = null;
            _prefabLoadSource = null;
            _activeCount = 0;
            _lastPrefabTouchTime = 0f;
        }

        private static string SanitizeName(string value)
        {
            return string.IsNullOrWhiteSpace(value)
                ? "Unnamed"
                : value.Replace('/', '_').Replace('\\', '_').Replace(':', '_');
        }
    }
}