using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Reflection;
using System.Resources;
using System.Threading;
using Prism.Events;
using XP.Common.Localization.Enums;
using XP.Common.Localization.Events;
using XP.Common.Localization.Interfaces;
using XP.Common.Logging.Interfaces;

namespace XP.Common.Localization.Implementations
{
    /// <summary>
    /// Resx 本地化服务实现 | Resx localization service implementation
    /// 使用 .NET ResourceManager 加载 Resx 资源文件 | Uses .NET ResourceManager to load Resx resource files
    /// 支持多资源源 Fallback Chain 机制 | Supports multi-source Fallback Chain mechanism
    /// </summary>
    public class ResxLocalizationService : ILocalizationService
    {
        private readonly List<ResourceSource> _resourceSources = new List<ResourceSource>();
        private readonly ReaderWriterLockSlim _rwLock = new ReaderWriterLockSlim();
        private readonly IEventAggregator _eventAggregator;
        private readonly ILocalizationConfig _config;
        private readonly ILoggerService _logger;
        private SupportedLanguage _currentLanguage;

        /// <summary>
        /// 获取当前语言 | Get current language
        /// </summary>
        public SupportedLanguage CurrentLanguage => _currentLanguage;

        /// <summary>
        /// 语言切换事件 | Language changed event
        /// </summary>
        public event EventHandler<LanguageChangedEventArgs>? LanguageChanged;

        /// <summary>
        /// 构造函数 | Constructor
        /// </summary>
        /// <param name="eventAggregator">事件聚合器 | Event aggregator</param>
        /// <param name="config">本地化配置 | Localization configuration</param>
        /// <param name="logger">日志服务 | Logger service</param>
        public ResxLocalizationService(
            IEventAggregator eventAggregator,
            ILocalizationConfig config,
            ILoggerService logger)
        {
            _eventAggregator = eventAggregator ?? throw new ArgumentNullException(nameof(eventAggregator));
            _config = config ?? throw new ArgumentNullException(nameof(config));
            _logger = (logger ?? throw new ArgumentNullException(nameof(logger))).ForModule<ResxLocalizationService>();

            // 初始化默认资源源（XP.Common），注册到 Fallback Chain[0]
            // Initialize default resource source (XP.Common), registered at Fallback Chain[0]
            var defaultResourceManager = new ResourceManager(
                "XP.Common.Resources.Resources",
                Assembly.GetExecutingAssembly());
            _resourceSources.Add(new ResourceSource("XP.Common", defaultResourceManager));

            // 加载保存的语言或使用默认语言 | Load saved language or use default language
            InitializeLanguage();
        }

        /// <summary>
        /// 获取本地化字符串（使用当前语言）| Get localized string (using current language)
        /// </summary>
        /// <param name="key">资源键 | Resource key</param>
        /// <returns>本地化字符串 | Localized string</returns>
        public string GetString(string key)
        {
            return GetString(key, CultureInfo.CurrentUICulture);
        }

        /// <summary>
        /// 获取本地化字符串（指定语言）| Get localized string (specified language)
        /// 从 Fallback Chain 末尾向前遍历，第一个返回非 null 值的 ResourceManager 即为结果
        /// Traverses the Fallback Chain from end to beginning, first ResourceManager returning non-null wins
        /// </summary>
        /// <param name="key">资源键 | Resource key</param>
        /// <param name="culture">文化信息 | Culture info</param>
        /// <returns>本地化字符串 | Localized string</returns>
        public string GetString(string key, CultureInfo culture)
        {
            if (string.IsNullOrEmpty(key))
            {
                return string.Empty;
            }

            _rwLock.EnterReadLock();
            try
            {
                // 从末尾向前遍历（后注册 = 高优先级）
                // Traverse from end to beginning (last registered = highest priority)
                for (int i = _resourceSources.Count - 1; i >= 0; i--)
                {
                    try
                    {
                        var value = _resourceSources[i].ResourceManager.GetString(key, culture);
                        if (value != null)
                        {
                            return value;
                        }
                    }
                    catch (Exception ex)
                    {
                        // 单个 ResourceManager 抛出异常时捕获并继续遍历下一个
                        // Catch exception from individual ResourceManager and continue to next
                        _logger.Error(ex, $"资源源 '{_resourceSources[i].Name}' 查找键 '{key}' 时出错 | Error looking up key '{key}' in resource source '{_resourceSources[i].Name}'");
                    }
                }
            }
            finally
            {
                _rwLock.ExitReadLock();
            }

            // 全部未找到则返回 key 本身并记录警告日志
            // If all sources fail to find the key, return the key itself and log warning
            _logger.Warn($"资源键未找到 | Resource key not found: '{key}' for culture '{culture?.Name ?? "null"}'");
            return key;
        }

        /// <summary>
        /// 注册模块资源源到 Fallback Chain 末尾（最高优先级）
        /// Register a module resource source to the end of the Fallback Chain (highest priority)
        /// </summary>
        /// <param name="name">资源源名称 | Resource source name</param>
        /// <param name="resourceManager">模块的 ResourceManager 实例 | Module's ResourceManager instance</param>
        public void RegisterResourceSource(string name, ResourceManager resourceManager)
        {
            if (name == null) throw new ArgumentNullException(nameof(name));
            if (resourceManager == null) throw new ArgumentNullException(nameof(resourceManager));

            _rwLock.EnterWriteLock();
            try
            {
                // 检查重复名称 | Check for duplicate name
                if (_resourceSources.Any(s => s.Name == name))
                {
                    _logger.Warn($"资源源 '{name}' 已存在，注册被拒绝 | Resource source '{name}' already exists, registration rejected");
                    throw new InvalidOperationException($"Resource source '{name}' is already registered.");
                }

                _resourceSources.Add(new ResourceSource(name, resourceManager));
                _logger.Info($"资源源 '{name}' 已注册到 Fallback Chain | Resource source '{name}' registered to Fallback Chain");
            }
            finally
            {
                _rwLock.ExitWriteLock();
            }
        }

        /// <summary>
        /// 从 Fallback Chain 中注销指定资源源
        /// Unregister the specified resource source from the Fallback Chain
        /// </summary>
        /// <param name="name">资源源名称 | Resource source name</param>
        public void UnregisterResourceSource(string name)
        {
            if (name == null) throw new ArgumentNullException(nameof(name));

            // 禁止注销默认资源源 | Prevent unregistering default resource source
            if (name == "XP.Common")
            {
                throw new InvalidOperationException("Cannot unregister the default resource source 'XP.Common'.");
            }

            _rwLock.EnterWriteLock();
            try
            {
                var source = _resourceSources.FirstOrDefault(s => s.Name == name);
                if (source != null)
                {
                    _resourceSources.Remove(source);
                    _logger.Info($"资源源 '{name}' 已从 Fallback Chain 注销 | Resource source '{name}' unregistered from Fallback Chain");
                }
                else
                {
                    // 注销不存在的名称时静默忽略，记录警告日志
                    // Silently ignore non-existent name, log warning
                    _logger.Warn($"资源源 '{name}' 不存在，注销操作被忽略 | Resource source '{name}' does not exist, unregister ignored");
                }
            }
            finally
            {
                _rwLock.ExitWriteLock();
            }
        }

        /// <summary>
        /// 设置当前语言（仅保存配置，重启后生效）| Set current language (save config only, takes effect after restart)
        /// </summary>
        /// <param name="language">目标语言 | Target language</param>
        public void SetLanguage(SupportedLanguage language)
        {
            _rwLock.EnterWriteLock();
            try
            {
                // 如果语言相同，无需保存 | If language is the same, no need to save
                if (_currentLanguage == language)
                {
                    _logger.Info($"语言已经是 {language}，无需切换 | Language is already {language}, no need to switch");
                    return;
                }

                try
                {
                    _logger.Info($"保存语言设置，重启后生效 | Saving language setting, takes effect after restart: {_currentLanguage} -> {language}");

                    // 仅保存到配置，不更新运行时状态 | Only save to config, do not update runtime state
                    _config.SaveLanguage(language);

                    _logger.Info($"语言设置已保存 | Language setting saved: {language}");
                }
                catch (Exception ex)
                {
                    _logger.Error(ex, $"语言设置保存失败 | Failed to save language setting: {language}");
                    throw;
                }
            }
            finally
            {
                _rwLock.ExitWriteLock();
            }
        }

        /// <summary>
        /// 获取所有支持的语言 | Get all supported languages
        /// </summary>
        /// <returns>支持的语言列表 | List of supported languages</returns>
        public IEnumerable<SupportedLanguage> GetSupportedLanguages()
        {
            return Enum.GetValues(typeof(SupportedLanguage))
                       .Cast<SupportedLanguage>();
        }

        /// <summary>
        /// 初始化语言设置 | Initialize language settings
        /// </summary>
        private void InitializeLanguage()
        {
            try
            {
                // 尝试获取保存的语言 | Try to get saved language
                var savedLanguage = _config.GetSavedLanguage();
                var language = savedLanguage ?? _config.GetSystemDefaultLanguage();

                _currentLanguage = language;
                var culture = GetCultureInfo(language);
                CultureInfo.CurrentUICulture = culture;
                CultureInfo.CurrentCulture = culture;

                _logger.Info($"语言初始化完成 | Language initialized: {language} (Culture: {culture.Name})");

                // 验证资源文件是否可加载 | Verify resource file can be loaded
                ValidateResourceFile(culture);
            }
            catch (Exception ex)
            {
                _logger.Error(ex, "语言初始化失败 | Language initialization failed");
                throw;
            }
        }

        /// <summary>
        /// 获取语言对应的 CultureInfo | Get CultureInfo for language
        /// </summary>
        /// <param name="language">支持的语言 | Supported language</param>
        /// <returns>文化信息 | Culture info</returns>
        private CultureInfo GetCultureInfo(SupportedLanguage language)
        {
            return language switch
            {
                SupportedLanguage.ZhCN => new CultureInfo("zh-CN"),
                SupportedLanguage.ZhTW => new CultureInfo("zh-TW"),
                SupportedLanguage.EnUS => new CultureInfo("en-US"),
                _ => new CultureInfo("zh-CN") // 默认简体中文 | Default to Simplified Chinese
            };
        }

        /// <summary>
        /// 验证资源文件是否可加载 | Validate resource file can be loaded
        /// 使用默认资源源（XP.Common）进行验证 | Uses default resource source (XP.Common) for validation
        /// </summary>
        /// <param name="culture">文化信息 | Culture info</param>
        private void ValidateResourceFile(CultureInfo culture)
        {
            try
            {
                // 使用第一个资源源（XP.Common）进行验证
                // Use the first resource source (XP.Common) for validation
                var testValue = _resourceSources[0].ResourceManager.GetString("App_Title", culture);

                if (testValue != null)
                {
                    _logger.Info($"资源文件验证成功 | Resource file validated for culture: {culture.Name}");
                }
                else
                {
                    _logger.Warn($"资源文件可能不完整 | Resource file may be incomplete for culture: {culture.Name}");
                }
            }
            catch (Exception)
            {
                _logger.Warn($"资源文件验证失败，将使用默认资源 | Resource file validation failed, will use default resources for culture: {culture.Name}");
            }
        }
    }
}