using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.ResourceManagement.AsyncOperations;
using Object = UnityEngine.Object;

namespace AibisDream.Framework
{
    /// <summary>
    /// 资源加载系统静态门面。管理 Persistent / Scene 两级 Loader，提供面向业务的统一 API。
    /// 调用方可通过 LoadAsync（自动路由）、LoadPersistentAsync（显式持久化）、LoadSceneAsync（显式场景级）选择目标。
    /// </summary>
    public static class ResourceSystem
    {
        private static SceneResourceLoader _persistentLoader;
        private static SceneResourceLoader _sceneLoader;

        #region Loader Management

        /// <summary>
        /// 创建场景级 Loader。由 SceneLoader 在场景加载完成后调用。
        /// </summary>
        public static void CreateSceneLoader()
        {
            if (_sceneLoader != null)
            {
                Debug.LogWarning("[ResourceSystem] Previous scene loader exists, releasing it.");
                _sceneLoader.Dispose();
            }
            _sceneLoader = new SceneResourceLoader(isPersistent: false);
            Debug.Log("[ResourceSystem] Scene loader created.");
        }

        /// <summary>
        /// 释放场景级 Loader。由 SceneLoader 在场景卸载前调用。
        /// </summary>
        public static void ReleaseSceneLoader()
        {
            if (_sceneLoader != null)
            {
                int releasedCount = _sceneLoader.TotalHandleCount;
                _sceneLoader.Dispose();
                _sceneLoader = null;
                Debug.Log($"[ResourceSystem] Scene loader released. {releasedCount} handles released.");
            }
        }

        /// <summary>
        /// 懒加载 Persistent Loader。首次调用 LoadPersistentAsync 时自动创建。
        /// </summary>
        private static void EnsurePersistentLoader()
        {
            if (_persistentLoader == null)
            {
                _persistentLoader = new SceneResourceLoader(isPersistent: true);
                Debug.Log("[ResourceSystem] Persistent loader created (lazy).");
            }
        }

        #endregion

        #region Loader Access

        public static SceneResourceLoader PersistentLoader => _persistentLoader;
        public static SceneResourceLoader CurrentSceneLoader => _sceneLoader;

        private static SceneResourceLoader ActiveLoader
        {
            get
            {
                if (_sceneLoader != null) return _sceneLoader;
                if (_persistentLoader != null) return _persistentLoader;
                Debug.LogError("[ResourceSystem] No loader available. Ensure SceneLoader.CreateSceneLoader() was called.");
                return null;
            }
        }

        #endregion

        #region Auto-Routed API (uses ActiveLoader: scene first, falls back to persistent)

        public static AsyncOperationHandle<T> LoadAsync<T>(string key) where T : Object
            => ActiveLoader.LoadAsync<T>(key);

        public static void LoadAsync<T>(string key, Action<T> onComplete, Action<string> onError = null) where T : Object
            => ActiveLoader.LoadAsync(key, onComplete, onError);

        #endregion

        #region Persistent Loader API

        public static AsyncOperationHandle<T> LoadPersistentAsync<T>(string key) where T : Object
        {
            EnsurePersistentLoader();
            return _persistentLoader.LoadAsync<T>(key);
        }

        public static void LoadPersistentAsync<T>(string key, Action<T> onComplete, Action<string> onError = null)
            where T : Object
        {
            EnsurePersistentLoader();
            _persistentLoader.LoadAsync(key, onComplete, onError);
        }

        #endregion

        #region Scene Loader API

        public static AsyncOperationHandle<T> LoadSceneAsync<T>(string key) where T : Object
        {
            if (_sceneLoader == null)
            {
                Debug.LogError("[ResourceSystem] No scene loader. Ensure CreateSceneLoader() was called by SceneLoader.");
                return default;
            }
            return _sceneLoader.LoadAsync<T>(key);
        }

        public static void LoadSceneAsync<T>(string key, Action<T> onComplete, Action<string> onError = null)
            where T : Object
        {
            if (_sceneLoader == null)
            {
                Debug.LogError("[ResourceSystem] No scene loader. Ensure CreateSceneLoader() was called by SceneLoader.");
                return;
            }
            _sceneLoader.LoadAsync(key, onComplete, onError);
        }

        #endregion

        #region Preload & Release

        public static AsyncOperationHandle<IList<T>> PreloadByLabel<T>(string label) where T : Object
            => ActiveLoader.PreloadByLabel<T>(label);

        public static void EarlyRelease(string key)
            => ActiveLoader.EarlyRelease(key);

        public static void EarlyRelease<T>(AsyncOperationHandle<T> handle)
            => ActiveLoader.EarlyRelease(handle);

        #endregion
    }
}