using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;
using Newtonsoft.Json;
using TeamAAS.Database.Attributes;
using TeamAAS.Database.Interfaces;
using TeamAAS.Database.Models;

namespace TeamAAS.Database
{
    /// <summary>
    /// 数据库管理器。
    /// 负责多数据库实例的创建、注册、移除、配置持久化以及提供者反射发现。
    /// 懒汉单例模式：DatabaseManager.Instance
    /// </summary>
    public class DatabaseManager : IDatabaseManager
    {
        #region 单例

        private static readonly Lazy<DatabaseManager> _instance =
            new Lazy<DatabaseManager>(() => new DatabaseManager(), isThreadSafe: true);

        /// <summary>
        /// 懒汉单例入口。首次访问时初始化，线程安全。
        /// </summary>
        public static DatabaseManager Instance => _instance.Value;

        #endregion

        #region 字段

        private readonly Dictionary<Guid, IDatabase> _databases;
        private readonly object _sync = new object();

        // 反射扫描的提供者缓存
        private List<DatabaseProviderInfo> _providers;
        private readonly object _providerLock = new object();

        // 配置文件路径
        private string _configPath;

        #endregion

        #region 构造

        public DatabaseManager()
        {
            _databases = new Dictionary<Guid, IDatabase>();
        }

        #endregion

        #region 提供者发现

        /// <summary>
        /// 获取所有可用的数据库提供者（反射扫描当前程序集及已加载程序集中的 IDatabase 实现）
        /// </summary>
        public List<DatabaseProviderInfo> GetAvailableProviders()
        {
            lock (_providerLock)
            {
                if (_providers != null)
                    return _providers.ToList();

                _providers = new List<DatabaseProviderInfo>();

                try
                {
                    // 反射扫描:收集全部 IDatabase 实现(当前程序集 + 同级目录下的 DLL)
                    foreach (var type in ScanImplementations<IDatabase>())
                    {
                        var attr = type.GetCustomAttribute<DatabaseProviderAttribute>();
                        if (attr == null)
                            continue;

                        _providers.Add(new DatabaseProviderInfo
                        {
                            ProviderType = attr.ProviderType,
                            DisplayName = attr.DisplayName,
                            ImplementationType = type,
                            RequiresServer = attr.RequiresServer,
                            Description = attr.Description
                        });
                    }
                }
                catch { /* 提供者扫描失败不抛异常 */ }

                return _providers.ToList();
            }
        }

        /// <summary>
        /// 根据 providerType 创建数据库实例
        /// </summary>
        private IDatabase CreateDatabaseInstance(DatabaseConfig config)
        {
            var providers = GetAvailableProviders();
            var provider = providers.FirstOrDefault(
                p => string.Equals(p.ProviderType, config.ProviderType, StringComparison.OrdinalIgnoreCase));

            if (provider == null)
                throw new InvalidOperationException($"未找到数据库提供者：{config.ProviderType}");

            var instance = (IDatabase)Activator.CreateInstance(provider.ImplementationType);
            instance.Configure(config);
            return instance;
        }

        #endregion

        #region 反射扫描辅助

        /// <summary>
        /// 扫描当前程序集及应用程序基目录下所有 DLL，查找实现了 TInterface 的非抽象类。
        /// </summary>
        private static List<Type> ScanImplementations<TInterface>()
        {
            var result = new List<Type>();
            var interfaceType = typeof(TInterface);

            // 1. 当前程序集
            var currentAsm = Assembly.GetExecutingAssembly();
            ScanAssembly(currentAsm, interfaceType, result);

            // 2. 应用程序基目录下的其他 DLL（支持插件扩展）
            try
            {
                string baseDir = AppDomain.CurrentDomain.BaseDirectory;
                foreach (var dll in Directory.GetFiles(baseDir, "*.dll", SearchOption.TopDirectoryOnly))
                {
                    try
                    {
                        var asmName = AssemblyName.GetAssemblyName(dll);
                        if (asmName.FullName == currentAsm.FullName)
                            continue; // 已扫描过

                        var asm = Assembly.Load(asmName);
                        ScanAssembly(asm, interfaceType, result);
                    }
                    catch { /* 单个 DLL 加载失败跳过 */ }
                }
            }
            catch { /* 目录扫描失败跳过 */ }

            return result;
        }

        private static void ScanAssembly(Assembly asm, Type interfaceType, List<Type> result)
        {
            try
            {
                foreach (var type in asm.GetTypes())
                {
                    if (type.IsAbstract || type.IsInterface || !type.IsClass)
                        continue;
                    if (!interfaceType.IsAssignableFrom(type))
                        continue;
                    result.Add(type);
                }
            }
            catch { /* 反射获取类型失败跳过 */ }
        }

        #endregion

        #region 数据库生命周期

        public bool CreateDatabase(Guid id, DatabaseConfig config)
        {
            if (config == null) throw new ArgumentNullException(nameof(config));
            if (string.IsNullOrWhiteSpace(config.ProviderType))
                throw new ArgumentException("ProviderType 不能为空", nameof(config));

            var database = CreateDatabaseInstance(config);

            IDatabase existing = null;
            lock (_sync)
            {
                _databases.TryGetValue(id, out existing);
                _databases[id] = database;
            }

            if (existing != null && !ReferenceEquals(existing, database))
            {
                try { existing.Dispose(); } catch { }
            }

            return true;
        }

        public Task<bool> CreateDatabaseAsync(Guid id, DatabaseConfig config)
        {
            return Task.Run(() => CreateDatabase(id, config));
        }

        public IDatabase GetDatabase(Guid id)
        {
            lock (_sync)
            {
                return _databases.TryGetValue(id, out var db) ? db : null;
            }
        }

        public bool TryGetDatabase(Guid id, out IDatabase database)
        {
            lock (_sync)
            {
                return _databases.TryGetValue(id, out database);
            }
        }

        public bool ContainsDatabase(Guid id)
        {
            lock (_sync)
            {
                return _databases.ContainsKey(id);
            }
        }

        public IReadOnlyCollection<IDatabase> GetAllDatabases()
        {
            lock (_sync)
            {
                return _databases.Values.ToList().AsReadOnly();
            }
        }

        public bool RemoveDatabase(Guid id)
        {
            IDatabase db = null;
            lock (_sync)
            {
                if (_databases.TryGetValue(id, out db))
                    _databases.Remove(id);
            }

            if (db != null)
            {
                try { db.Dispose(); } catch { }
                return true;
            }

            return false;
        }

        public Task<bool> RemoveDatabaseAsync(Guid id)
        {
            return Task.Run(() => RemoveDatabase(id));
        }

        public void RemoveAllDatabases()
        {
            List<IDatabase> all;
            lock (_sync)
            {
                all = _databases.Values.ToList();
                _databases.Clear();
            }

            foreach (var db in all)
            {
                try { db.Dispose(); } catch { }
            }
        }

        public (bool IsSucceed, string Message) InitializeAllDatabases(DatabaseConfig[] configs)
        {
            if (configs == null) return (true, "无配置");

            var errors = new List<string>();
            var successCount = 0;

            foreach (var config in configs)
            {
                try
                {
                    var id = config.Id == Guid.Empty ? Guid.NewGuid() : config.Id;
                    CreateDatabase(id, config);
                    successCount++;
                }
                catch (Exception ex)
                {
                    errors.Add($"{config.Name ?? config.ProviderType}: {ex.Message}");
                }
            }

            if (errors.Count == 0)
                return (true, $"成功初始化 {successCount} 个数据库");

            return (false, $"成功 {successCount} 个，失败 {errors.Count} 个：{string.Join("; ", errors)}");
        }

        public Task<(bool IsSucceed, string Message)> InitializeAllDatabasesAsync(DatabaseConfig[] configs)
        {
            return Task.Run(() => InitializeAllDatabases(configs));
        }

        public IReadOnlyList<DatabaseConfig> GetAllDatabaseConfigs()
        {
            var result = new List<DatabaseConfig>();
            lock (_sync)
            {
                foreach (var db in _databases.Values)
                {
                    result.Add(new DatabaseConfig
                    {
                        Id = db.Id,
                        Name = db.Name,
                        ProviderType = db.ProviderType,
                        ConnectionString = db.ConnectionString
                    });
                }
            }
            return result.AsReadOnly();
        }

        #endregion

        #region 配置持久化

        /// <summary>
        /// 保存配置到 JSON 文件
        /// </summary>
        public bool SaveConfig(string path = null)
        {
            try
            {
                var filePath = path ?? _configPath;
                if (string.IsNullOrWhiteSpace(filePath))
                    throw new ArgumentException("配置文件路径不能为空", nameof(path));

                _configPath = filePath;
                var configs = GetAllDatabaseConfigs();
                var json = JsonConvert.SerializeObject(configs, Formatting.Indented);

                var dir = Path.GetDirectoryName(filePath);
                if (!string.IsNullOrWhiteSpace(dir) && !Directory.Exists(dir))
                    Directory.CreateDirectory(dir);

                File.WriteAllText(filePath, json);
                return true;
            }
            catch
            {
                return false;
            }
        }

        /// <summary>
        /// 从 JSON 文件加载配置并初始化
        /// </summary>
        public (bool IsSucceed, string Message) LoadConfig(string path)
        {
            try
            {
                if (!File.Exists(path))
                    return (false, $"配置文件不存在：{path}");

                _configPath = path;
                var json = File.ReadAllText(path);
                var configs = JsonConvert.DeserializeObject<DatabaseConfig[]>(json);

                if (configs == null || configs.Length == 0)
                    return (true, "配置为空");

                return InitializeAllDatabases(configs);
            }
            catch (Exception ex)
            {
                return (false, $"加载配置失败：{ex.Message}");
            }
        }

        #endregion

        #region IDisposable

        private bool _disposed;

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (_disposed) return;

            if (disposing)
            {
                RemoveAllDatabases();
            }

            _disposed = true;
        }

        ~DatabaseManager()
        {
            Dispose(false);
        }

        #endregion
    }
}