test/Assets/PerfectWorld/Scripts/PoolingManager/Prefabs/PrefabPoolManager.cs

using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.Pool;

/// <summary>
/// Centralized prefab pooling manager for reusable GameObject instances.
/// </summary>
///
namespace BrewMonster.Scripts
{
    public class PrefabPoolManager : MonoBehaviour
    {
        private static PrefabPoolManager instance;

        private readonly Dictionary<GameObject, PoolRecord> poolsByPrefab = new();
        private readonly Dictionary<GameObject, PoolRecord> allInstances = new();
        private readonly Dictionary<GameObject, PoolRecord> activeInstances = new();

        public static PrefabPoolManager Instance
        {
            get
            {
                if (instance == null)
                {
                    instance = FindAnyObjectByType<PrefabPoolManager>();
                    if (instance == null)
                    {
                        var managerObject = new GameObject(nameof(PrefabPoolManager));
                        instance = managerObject.AddComponent<PrefabPoolManager>();
                    }
                }

                return instance;
            }
        }

        public void InitPool(GameObject prefab, int defaultCapacity = 10, int maxSize = 50)
        {
            if (prefab == null)
            {
                Debug.LogError("[PrefabPoolManager] Cannot initialize a pool with a null prefab.");
                return;
            }

            if (poolsByPrefab.ContainsKey(prefab))
                return;

            defaultCapacity = Mathf.Max(0, defaultCapacity);
            maxSize = Mathf.Max(1, maxSize);
            if (defaultCapacity > maxSize)
                defaultCapacity = maxSize;

            var record = new PoolRecord
            {
                Prefab = prefab,
                Container = CreatePoolContainer(prefab)
            };

            record.Pool = new ObjectPool<GameObject>(
                () => CreateInstance(record),
                obj => OnGetFromPool(record, obj),
                obj => OnReleaseToPool(record, obj),
                OnDestroyPooledObject,
                collectionCheck: Application.isEditor,
                defaultCapacity: defaultCapacity,
                maxSize: maxSize);

            poolsByPrefab.Add(prefab, record);
            Prewarm(record, defaultCapacity);
        }

        public GameObject Spawn(GameObject prefab, Vector3 position, Quaternion rotation, Transform parent = null)
        {
            if (prefab == null)
            {
                Debug.LogError("[PrefabPoolManager] Cannot spawn a null prefab.");
                return null;
            }

            if (!poolsByPrefab.TryGetValue(prefab, out PoolRecord record))
            {
                InitPool(prefab);
                record = poolsByPrefab[prefab];
            }

            GameObject instanceObject = record.Pool.Get();
            instanceObject.transform.SetPositionAndRotation(position, rotation);
            if (parent != null)
            {
                instanceObject.transform.SetParent(parent);
            }
            return instanceObject;
        }

        public void Despawn(GameObject obj)
        {
            if (obj == null)
                return;

            if (!activeInstances.TryGetValue(obj, out PoolRecord record))
            {
                if (allInstances.ContainsKey(obj))
                {
                    Debug.LogWarning($"[PrefabPoolManager] Object '{obj.name}' has already been returned to the pool.");
                    return;
                }

                Debug.LogWarning($"[PrefabPoolManager] Object '{obj.name}' was not spawned by PrefabPoolManager. Destroying it instead.");
                Destroy(obj);
                return;
            }

            record.Pool.Release(obj);
        }

        private void Awake()
        {
            if (instance != null && instance != this)
            {
                Destroy(gameObject);
                return;
            }

            instance = this;
            //DontDestroyOnLoad(gameObject);
        }

        private void OnDestroy()
        {
            if (instance != this)
                return;

            foreach (PoolRecord record in poolsByPrefab.Values)
            {
                record.Pool.Clear();
            }

            poolsByPrefab.Clear();
            allInstances.Clear();
            activeInstances.Clear();
            instance = null;
        }

        private Transform CreatePoolContainer(GameObject prefab)
        {
            var container = new GameObject($"{prefab.name}_Pool").transform;
            container.SetParent(transform);
            return container;
        }

        private GameObject CreateInstance(PoolRecord record)
        {
            GameObject instanceObject = Instantiate(record.Prefab, record.Container);
            instanceObject.name = record.Prefab.name;
            instanceObject.SetActive(false);
            allInstances[instanceObject] = record;
            return instanceObject;
        }

        private void OnGetFromPool(PoolRecord record, GameObject obj)
        {
            activeInstances[obj] = record;
            obj.transform.SetParent(null);
            obj.SetActive(true);
        }

        private void OnReleaseToPool(PoolRecord record, GameObject obj)
        {
            activeInstances.Remove(obj);
            obj.SetActive(false);
            obj.transform.SetParent(record.Container);
        }

        private void OnDestroyPooledObject(GameObject obj)
        {
            activeInstances.Remove(obj);
            allInstances.Remove(obj);

            if (obj != null)
                Destroy(obj);
        }

        private static void Prewarm(PoolRecord record, int count)
        {
            if (count <= 0)
                return;

            var warmedObjects = new List<GameObject>(count);
            for (int i = 0; i < count; i++)
            {
                warmedObjects.Add(record.Pool.Get());
            }

            for (int i = 0; i < warmedObjects.Count; i++)
            {
                record.Pool.Release(warmedObjects[i]);
            }
        }

        internal sealed class PoolRecord
        {
            public GameObject Prefab;
            public Transform Container;
            public ObjectPool<GameObject> Pool;
        }
    }
}