using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace XWorld.Server.Host
{
    // (gameId,version) -> 已加载模块；按引用计数获取/释放。
    // 淘汰有两个来源：①同 gameId 更高版本加载成功；②同 (gameId,version) 磁盘内容指纹变化（覆盖重发）。
    // 被淘汰且引用归零即卸载；内容变化时新旧模块并存至旧房间结束（_retired，Release 按实例识别）。
    // 生产环境版本不可变、指纹恒命中缓存，行为与旧实现一致。
    public sealed class GameModuleRegistry
    {
        private sealed class Entry
        {
            public LoadedGameModule Module;
            public int RefCount;
            public bool Superseded;
            public string Fingerprint;
        }

        private readonly GameModuleLoader _loader;
        private readonly string _gamesRoot;
        private readonly Dictionary<string, Entry> _current = new Dictionary<string, Entry>();
        private readonly List<Entry> _retired = new List<Entry>();

        public GameModuleRegistry(GameModuleLoader loader, string gamesRoot)
        {
            _loader = loader; _gamesRoot = gamesRoot;
        }

        private static string Key(string gameId, int version) => $"{gameId}@{version}";
        private string ModuleDir(string gameId, int version) => Path.Combine(_gamesRoot, gameId, version.ToString());

        public LoadedGameModule Acquire(string gameId, int version)
        {
            string key = Key(gameId, version);
            if (_current.TryGetValue(key, out var e))
            {
                // 覆盖重发检测：磁盘内容指纹变化 → 旧条目退役、加载新内容。
                // 指纹算不出（目录处于覆盖交换的瞬间窗口/被删）→ 视为未变化，用缓存兜底。
                string fp = ComputeFingerprintOrNull(ModuleDir(gameId, version));
                if (fp == null || fp == e.Fingerprint)
                {
                    e.RefCount++;
                    return e.Module;
                }

                var reloaded = LoadEntry(gameId, version); // 失败直接抛出：旧条目原样保留，不污染状态
                Retire(e);
                _current[key] = reloaded;
                SupersedeOlderVersions(gameId, version);
                reloaded.RefCount++;
                return reloaded.Module;
            }

            var loaded = LoadEntry(gameId, version);
            _current[key] = loaded;
            SupersedeOlderVersions(gameId, version);
            loaded.RefCount++;
            return loaded.Module;
        }

        public void Release(LoadedGameModule module)
        {
            string key = Key(module.GameId, module.Version);
            if (_current.TryGetValue(key, out var e) && ReferenceEquals(e.Module, module))
            {
                if (e.RefCount <= 0)
                    throw new InvalidOperationException($"重复释放模块 {module.GameId}@{module.Version}");
                e.RefCount--;
                if (e.RefCount <= 0 && e.Superseded)
                {
                    _current.Remove(key);
                    module.Unload();
                }
                return;
            }

            // 退役条目：同版本被覆盖重发淘汰后仍被旧房间持有，按实例识别
            for (int i = 0; i < _retired.Count; i++)
            {
                if (!ReferenceEquals(_retired[i].Module, module)) continue;
                var r = _retired[i];
                if (r.RefCount <= 0)
                    throw new InvalidOperationException($"重复释放模块 {module.GameId}@{module.Version}");
                r.RefCount--;
                if (r.RefCount <= 0)
                {
                    _retired.RemoveAt(i);
                    module.Unload();
                }
                return;
            }
            // 未知模块的释放忽略（与旧实现对不存在 key 直接 return 的行为一致）
        }

        public int RefCount(string gameId, int version)
            => _current.TryGetValue(Key(gameId, version), out var e) ? e.RefCount : 0;

        public bool IsLoaded(string gameId, int version) => _current.ContainsKey(Key(gameId, version));

        private Entry LoadEntry(string gameId, int version)
        {
            // 指纹在加载前采样：加载成功即与所载内容对应（单线程 tick actor 下无并发写窗口）
            string fp = ComputeFingerprintOrNull(ModuleDir(gameId, version));
            var loaded = _loader.Load(_gamesRoot, gameId, version);
            return new Entry { Module = loaded, RefCount = 0, Superseded = false, Fingerprint = fp };
        }

        private void SupersedeOlderVersions(string gameId, int version)
        {
            foreach (var kv in _current)
                if (kv.Value.Module.GameId == gameId && kv.Value.Module.Version < version)
                    kv.Value.Superseded = true;
        }

        private void Retire(Entry e)
        {
            e.Superseded = true;
            if (e.RefCount <= 0) e.Module.Unload();
            else _retired.Add(e);
        }

        // 目录内容指纹：全部 *.dll + game.json 按名 Ordinal 排序拼 name=md5; 再整体 md5；
        // 读不到（目录不存在/IO 竞态）返回 null 由调用方兜底
        private static string ComputeFingerprintOrNull(string dir)
        {
            try
            {
                if (!Directory.Exists(dir)) return null;
                var names = Directory.GetFiles(dir, "*.dll")
                    .Select(Path.GetFileName)
                    .Append("game.json")
                    .Where(n => File.Exists(Path.Combine(dir, n)))
                    .Distinct()
                    .OrderBy(n => n, StringComparer.Ordinal);
                var sb = new StringBuilder();
                foreach (var n in names)
                    sb.Append(n).Append('=')
                      .Append(XWorld.PublishTool.Md5Util.OfFile(Path.Combine(dir, n))).Append(';');
                return XWorld.PublishTool.Md5Util.OfBytes(Encoding.UTF8.GetBytes(sb.ToString()));
            }
            catch (IOException) { return null; }
            catch (UnauthorizedAccessException) { return null; }
        }
    }
}