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

namespace BrewMonster.Scripts
{
    internal sealed class ObjectPool
    {
        private readonly string _addressableKey;
        private readonly PoolManager _owner;
        private readonly AddressableManager _addressableManager;
        private readonly Transform _poolRoot;
        private readonly Stack<GameObject> _idleInstances = new();
        private readonly HashSet<GameObject> _activeInstances = new();
        private readonly HashSet<GameObject> _knownInstances = new();
        private readonly Dictionary<GameObject, int> _spawnVersions = new();

        private GameObject _prefab;
        private Task<GameObject> _loadTask;
        private Coroutine _releaseCoroutine;
        private float _memoryReleaseTTL;

        public ObjectPool(
            string addressableKey,
            PoolManager owner,
            AddressableManager addressableManager,
            Transform poolRoot,
            float memoryReleaseTTL)
        {
            _addressableKey = addressableKey;
            _owner = owner;
            _addressableManager = addressableManager;
            _poolRoot = poolRoot;
            _memoryReleaseTTL = Mathf.Max(0f, memoryReleaseTTL);
        }

        public string AddressableKey => _addressableKey;
        public int ActiveCount => _activeInstances.Count;
        public int IdleCount => _idleInstances.Count;

        public void UpdateMemoryReleaseTTL(float memoryReleaseTTL)
        {
            _memoryReleaseTTL = Mathf.Max(0f, memoryReleaseTTL);
        }

        public async Task<GameObject> SpawnAsync(Vector3 position, Quaternion rotation, Transform parent)
        {
            CancelReleaseCountdown();

            GameObject instance = GetIdleInstance();
            if (instance == null)
            {
                GameObject prefab = await LoadPrefabAsync();
                if (prefab == null)
                {
                    return null;
                }

                instance = Object.Instantiate(prefab);
                _knownInstances.Add(instance);
                _spawnVersions[instance] = 0;
            }

            _activeInstances.Add(instance);
            _spawnVersions[instance]++;
            instance.transform.SetParent(parent, true);
            instance.transform.SetPositionAndRotation(position, rotation);
            instance.SetActive(true);
            NotifyPoolablesSpawned(instance);

            return instance;
        }

        public bool Despawn(GameObject instance)
        {
            if (instance == null || !_activeInstances.Remove(instance))
            {
                return false;
            }

            NotifyPoolablesDespawned(instance);
            _spawnVersions[instance]++;
            instance.SetActive(false);
            instance.transform.SetParent(_poolRoot, false);
            _idleInstances.Push(instance);

            if (_activeInstances.Count == 0)
            {
                StartReleaseCountdown();
            }

            return true;
        }

        public bool IsActiveInstance(GameObject instance, int spawnVersion)
        {
            return instance != null
                && _activeInstances.Contains(instance)
                && _spawnVersions.TryGetValue(instance, out int currentVersion)
                && currentVersion == spawnVersion;
        }

        public int GetSpawnVersion(GameObject instance)
        {
            return instance != null && _spawnVersions.TryGetValue(instance, out int version) ? version : -1;
        }

        public IEnumerable<GameObject> GetKnownInstances()
        {
            return _knownInstances;
        }

        public void ReleaseNow()
        {
            CancelReleaseCountdown();
            DestroyAllInstances();
            ReleasePrefabAsset();
        }

        private GameObject GetIdleInstance()
        {
            while (_idleInstances.Count > 0)
            {
                GameObject instance = _idleInstances.Pop();
                if (instance != null)
                {
                    return instance;
                }
            }

            return null;
        }

        private async Task<GameObject> LoadPrefabAsync()
        {
            if (_prefab != null)
            {
                return _prefab;
            }

            if (_loadTask != null)
            {
                return await _loadTask;
            }

            _loadTask = LoadPrefabInternalAsync();
            GameObject prefab = await _loadTask;
            if (prefab == null)
            {
                _loadTask = null;
            }

            return prefab;
        }

        private async Task<GameObject> LoadPrefabInternalAsync()
        {
            if (_addressableManager == null)
            {
                BMLogger.LogError($"ObjectPool: AddressableManager is not available for '{_addressableKey}'.");
                return null;
            }

            await _addressableManager.WaitUntilInitializedAsync();

            GameObject prefab = await _addressableManager.LoadPrefabAsync(_addressableKey);
            if (prefab == null)
            {
                BMLogger.LogError($"ObjectPool: Failed to load Addressable prefab '{_addressableKey}'.");
                return null;
            }

            _prefab = prefab;
            return _prefab;
        }

        private void StartReleaseCountdown()
        {
            CancelReleaseCountdown();
            _releaseCoroutine = _owner.StartCoroutine(ReleaseMemoryCountdown());
        }

        private void CancelReleaseCountdown()
        {
            if (_releaseCoroutine == null)
            {
                return;
            }

            _owner.StopCoroutine(_releaseCoroutine);
            _releaseCoroutine = null;
        }

        private IEnumerator ReleaseMemoryCountdown()
        {
            if (_memoryReleaseTTL > 0f)
            {
                yield return new WaitForSecondsRealtime(_memoryReleaseTTL);
            }

            _releaseCoroutine = null;
            if (_activeInstances.Count > 0)
            {
                yield break;
            }

            _owner.RemovePool(this);
            DestroyAllInstances();
            ReleasePrefabAsset();
        }

        private void DestroyAllInstances()
        {
            foreach (GameObject instance in _knownInstances)
            {
                if (instance == null)
                {
                    continue;
                }

                if (_activeInstances.Contains(instance))
                {
                    NotifyPoolablesDespawned(instance);
                }

                Object.Destroy(instance);
            }

            _idleInstances.Clear();
            _activeInstances.Clear();
            _knownInstances.Clear();
            _spawnVersions.Clear();

            if (_poolRoot != null)
            {
                Object.Destroy(_poolRoot.gameObject);
            }
        }

        private void ReleasePrefabAsset()
        {
            if (_prefab != null && _addressableManager != null)
            {
                _addressableManager.ReleaseAsset(_addressableKey);
            }

            _prefab = null;
            _loadTask = null;
        }

        private static void NotifyPoolablesSpawned(GameObject instance)
        {
            IPoolable[] poolables = instance.GetComponentsInChildren<IPoolable>(true);
            for (int i = 0; i < poolables.Length; i++)
            {
                poolables[i].OnSpawn();
            }
        }

        private static void NotifyPoolablesDespawned(GameObject instance)
        {
            IPoolable[] poolables = instance.GetComponentsInChildren<IPoolable>(true);
            for (int i = 0; i < poolables.Length; i++)
            {
                poolables[i].OnDespawn();
            }
        }
    }
}