using System.Collections.Generic;
using Cielonos.MainGame.Inventory;
using UnityEngine;

namespace Cielonos.MainGame.Items
{
    /// <summary>
    /// 从 Resources/Items 目录动态加载物品预制体，并提供加权随机抽取功能。
    /// 替代手动维护的 ScriptableObject 物品池，新增装备只需放入对应目录即可自动进入候选池。
    /// </summary>
    public static class ItemPoolHelper
    {
        private const string ITEMS_ROOT_PATH = "Items";

        private static readonly Dictionary<string, GameObject[]> prefabCache = new Dictionary<string, GameObject[]>();

        /// <summary>
        /// 从 Resources/Items 的指定子目录中加载所有带 ItemBase 的预制体，
        /// 按 ItemFilter 过滤后进行加权随机抽取（不重复）。
        /// </summary>
        /// <param name="count">需要抽取的数量。</param>
        /// <param name="rng">随机数生成器，确保同 seed 可复现。</param>
        /// <param name="filter">过滤器，传 null 则不过滤。</param>
        /// <param name="subFolders">Resources/Items 下的子目录名。不传则搜索整个 Items 目录。</param>
        /// <returns>抽中的物品预制体列表（不重复）。</returns>
        public static List<GameObject> Roll(int count, System.Random rng, ItemFilter filter = null, params string[] subFolders)
        {
            List<CandidateEntry> candidates = BuildCandidateList(filter, subFolders);
            return WeightedPick(candidates, count, rng);
        }

        /// <summary>
        /// 清除预制体缓存。可在场景切换或 Run 结束时调用。
        /// </summary>
        public static void ClearCache()
        {
            prefabCache.Clear();
        }

        private static List<CandidateEntry> BuildCandidateList(ItemFilter filter, string[] subFolders)
        {
            List<CandidateEntry> candidates = new List<CandidateEntry>();

            string[] paths = subFolders != null && subFolders.Length > 0
                ? subFolders
                : new[] { string.Empty };

            foreach (string sub in paths)
            {
                string resourcePath = string.IsNullOrEmpty(sub)
                    ? ITEMS_ROOT_PATH
                    : $"{ITEMS_ROOT_PATH}/{sub}";

                GameObject[] prefabs = LoadPrefabs(resourcePath);

                foreach (GameObject prefab in prefabs)
                {
                    ItemBase item = prefab.GetComponent<ItemBase>();
                    if (item == null || item.contentData == null) continue;

                    ContentData data = item.contentData;

                    // 权重为 0 的物品不进入随机池
                    if (data.dropWeight <= 0f) continue;

                    // 应用过滤器
                    if (filter != null && !filter.Match(item)) continue;

                    candidates.Add(new CandidateEntry(prefab, data));
                }
            }

            return candidates;
        }

        private static GameObject[] LoadPrefabs(string resourcePath)
        {
            if (prefabCache.TryGetValue(resourcePath, out GameObject[] cached))
            {
                return cached;
            }

            GameObject[] loaded = Resources.LoadAll<GameObject>(resourcePath);
            prefabCache[resourcePath] = loaded;
            return loaded;
        }

        private static List<GameObject> WeightedPick(List<CandidateEntry> candidates, int count, System.Random rng)
        {
            List<GameObject> results = new List<GameObject>();
            int pickCount = Mathf.Min(count, candidates.Count);

            for (int i = 0; i < pickCount; i++)
            {
                float totalWeight = 0f;
                foreach (CandidateEntry entry in candidates)
                {
                    totalWeight += entry.data.dropWeight;
                }

                if (totalWeight <= 0f) break;

                float roll = (float)(rng.NextDouble() * totalWeight);
                float cumulative = 0f;
                CandidateEntry picked = null;

                foreach (CandidateEntry entry in candidates)
                {
                    cumulative += entry.data.dropWeight;
                    if (roll <= cumulative)
                    {
                        picked = entry;
                        break;
                    }
                }

                // 安全回退
                picked ??= candidates[^1];

                results.Add(picked.prefab);
                candidates.Remove(picked);
            }

            return results;
        }

        private sealed class CandidateEntry
        {
            public readonly GameObject prefab;
            public readonly ContentData data;

            public CandidateEntry(GameObject prefab, ContentData data)
            {
                this.prefab = prefab;
                this.data = data;
            }
        }
    }
}