using LiveForum.Code.Redis.Contract;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace LiveForum.Code.SystemCache
{
    /// <summary>
    /// 系统缓存服务基类（用于底层支持需要的系统级缓存）
    /// </summary>
    /// <typeparam name="TValue">缓存值类型</typeparam>
    /// <typeparam name="TKey">键类型（用于从缓存值中提取键）</typeparam>
    public abstract class SystemCacheServiceBase<TValue, TKey> : ISystemCacheService<TValue>
        where TKey : notnull
    {
        protected readonly IRedisService _redisService;
        protected abstract string CacheKey { get; }
        protected abstract TimeSpan CacheExpiration { get; }

        protected SystemCacheServiceBase(IRedisService redisService)
        {
            _redisService = redisService;
        }

        /// <summary>
        /// 从缓存值中提取键（子类需要实现）
        /// </summary>
        /// <param name="value">缓存值</param>
        /// <returns>键</returns>
        protected abstract TKey GetKeyFromValue(TValue value);

        /// <summary>
        /// 从数据库加载所有数据（子类需要实现）
        /// </summary>
        /// <returns>数据列表</returns>
        protected abstract Task<List<TValue>> LoadFromDatabaseAsync();

        /// <summary>
        /// 获取所有缓存数据（从缓存或数据库加载）
        /// </summary>
        public virtual async Task<List<TValue>> GetAllAsync()
        {
            try
            {
                // 先从缓存获取
                var cachedData = await _redisService.GetAsync<List<TValue>>(CacheKey);
                if (cachedData != null && cachedData.Any())
                {
                    return cachedData;
                }

                // 缓存未命中，从数据库加载
                var data = await LoadFromDatabaseAsync();
                if (data != null && data.Any())
                {
                    // 写入缓存
                    await _redisService.SetAsync(CacheKey, data, CacheExpiration);
                }

                return data ?? new List<TValue>();
            }
            catch (Exception ex)
            {
                // 记录错误但不抛出异常，尝试从数据库加载
                // 可以在这里添加日志记录
                return await LoadFromDatabaseAsync() ?? new List<TValue>();
            }
        }

        /// <summary>
        /// 根据键获取缓存数据
        /// </summary>
        public virtual async Task<TValue> GetByKeyAsync(object key)
        {
            if (key == null)
            {
                return default(TValue);
            }

            var allData = await GetAllAsync();
            TKey keyValue;
            
            if (key is TKey directKey)
            {
                keyValue = directKey;
            }
            else
            {
                try
                {
                    keyValue = (TKey)Convert.ChangeType(key, typeof(TKey));
                }
                catch
                {
                    return default(TValue);
                }
            }
            
            return allData.FirstOrDefault(x => GetKeyFromValue(x).Equals(keyValue));
        }

        /// <summary>
        /// 清除缓存
        /// </summary>
        public virtual async Task ClearCacheAsync()
        {
            try
            {
                await _redisService.RemoveAsync(CacheKey);
            }
            catch
            {
                // 忽略缓存清除错误
            }
        }

        /// <summary>
        /// 刷新缓存（清除并重新加载）
        /// </summary>
        public virtual async Task RefreshCacheAsync()
        {
            await ClearCacheAsync();
            await GetAllAsync();
        }
    }
}