using FreeSql;

using LiveForum.Code.Base;
using LiveForum.Code.Redis.Contract;
using LiveForum.IService.Posts;
using LiveForum.Model;

using Microsoft.Extensions.Logging;

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.Json;
using System.Threading.Tasks;

namespace LiveForum.Service.Posts
{
    /// <summary>
    /// 浏览服务实现
    /// </summary>
    public class ViewService : IViewService
    {
        private readonly IRedisService _redisService;
        private readonly IBaseRepository<T_Posts> _postsRepository;
        private readonly ILogger<ViewService> _logger;

        // Redis键命名规则常量
        private const string VIEW_LIMIT_KEY_PREFIX = "view:limit:";
        private const string VIEW_COUNT_KEY_PREFIX = "view_count:";
        private const string VIEW_PENDING_OPERATIONS_KEY = "view:pending:operations";

        // 缓存过期时间
        private static readonly TimeSpan VIEW_LIMIT_TTL = TimeSpan.FromMinutes(10); // 10分钟限制
        private static readonly TimeSpan VIEW_COUNT_CACHE_EXPIRATION = TimeSpan.FromHours(24); // 浏览次数缓存24小时

        public ViewService(
            IRedisService redisService,
            IBaseRepository<T_Posts> postsRepository,
            ILogger<ViewService> logger)
        {
            _redisService = redisService;
            _postsRepository = postsRepository;
            _logger = logger;
        }

        /// <summary>
        /// 获取10分钟限制键
        /// </summary>
        private string GetViewLimitKey(long userId, long postId)
        {
            return $"{VIEW_LIMIT_KEY_PREFIX}{userId}:{postId}";
        }

        /// <summary>
        /// 获取浏览次数计数键
        /// </summary>
        private string GetViewCountKey(long postId)
        {
            return $"{VIEW_COUNT_KEY_PREFIX}{postId}";
        }

        /// <summary>
        /// 获取待处理操作Hash字段名
        /// </summary>
        private string GetPendingOperationField(long userId, long postId)
        {
            return $"{userId}:{postId}";
        }

        public async Task<bool> CanAddViewAsync(long userId, long postId)
        {
            try
            {
                // 1. 优先从Redis检查10分钟限制
                var limitKey = GetViewLimitKey(userId, postId);
                var exists = await _redisService.ExistsAsync(limitKey);

                if (exists)
                {
                    // Redis中存在限制标记，说明10分钟内已浏览过
                    return false;
                }

                // 2. Redis中没有，允许浏览
                return true;
            }
            catch (Exception ex)
            {
                // Redis异常时，允许浏览（降级策略）
                _logger.LogWarning(ex, "Redis检查浏览限制失败，降级允许浏览。UserId: {UserId}, PostId: {PostId}",
                    userId, postId);
                return true;
            }
        }

        public async Task<int> GetViewCountAsync(long postId)
        {
            try
            {
                // 1. 优先从Redis查询
                var countKey = GetViewCountKey(postId);
                var count = await _redisService.StringGetInt64Async(countKey);

                if (count > 0)
                {
                    return (int)count;
                }

                // 2. Redis中没有或为0，查询数据库
                var post = await _postsRepository.Select
                    .Where(x => x.Id == postId)
                    .FirstAsync();

                var dbCount = post?.ViewCount ?? 0;

                // 3. 将结果写入Redis缓存（如果计数大于0）
                if (dbCount > 0)
                {
                    await _redisService.StringSetAsync(countKey, dbCount, VIEW_COUNT_CACHE_EXPIRATION);
                }

                return dbCount;
            }
            catch (Exception ex)
            {
                // Redis异常时降级到数据库查询
                _logger.LogWarning(ex, "Redis查询浏览次数失败，降级到数据库查询。PostId: {PostId}",
                    postId);

                try
                {
                    var post = await _postsRepository.Select
                        .Where(x => x.Id == postId)
                        .FirstAsync();
                    return post?.ViewCount ?? 0;
                }
                catch (Exception dbEx)
                {
                    _logger.LogError(dbEx, "数据库查询浏览次数失败。PostId: {PostId}",
                        postId);
                    throw;
                }
            }
        }

        public async Task<Dictionary<long, int>> BatchGetViewCountAsync(List<long> postIds)
        {
            if (postIds == null || !postIds.Any())
            {
                return new Dictionary<long, int>();
            }

            var result = new Dictionary<long, int>();
            var needQueryFromDb = new List<long>();

            try
            {
                // 1. 批量从Redis查询
                foreach (var postId in postIds)
                {
                    var countKey = GetViewCountKey(postId);
                    var count = await _redisService.StringGetInt64Async(countKey);
                    result[postId] = (int)count;

                    if (count == 0)
                    {
                        needQueryFromDb.Add(postId);
                    }
                }

                // 2. 批量查询数据库中缺失的
                if (needQueryFromDb.Any())
                {
                    var posts = await _postsRepository.Select
                        .Where(x => needQueryFromDb.Contains(x.Id))
                        .ToListAsync();
                    var dbCounts = posts.ToDictionary(x => x.Id, x => x.ViewCount);

                    // 3. 更新结果并写入Redis缓存
                    foreach (var postId in needQueryFromDb)
                    {
                        var count = dbCounts.ContainsKey(postId) ? dbCounts[postId] : 0;
                        result[postId] = count;

                        if (count > 0)
                        {
                            var countKey = GetViewCountKey(postId);
                            await _redisService.StringSetAsync(countKey, count, VIEW_COUNT_CACHE_EXPIRATION);
                        }
                    }
                }

                return result;
            }
            catch (Exception ex)
            {
                // Redis异常时降级到数据库查询
                _logger.LogWarning(ex, "Redis批量查询浏览次数失败，降级到数据库查询。");

                try
                {
                    var posts = await _postsRepository.Select
                        .Where(x => postIds.Contains(x.Id))
                        .ToListAsync();
                    var dbCounts = posts.ToDictionary(x => x.Id, x => x.ViewCount);

                    foreach (var postId in postIds)
                    {
                        result[postId] = dbCounts.ContainsKey(postId) ? dbCounts[postId] : 0;
                    }

                    return result;
                }
                catch (Exception dbEx)
                {
                    _logger.LogError(dbEx, "数据库批量查询浏览次数失败。");
                    throw;
                }
            }
        }

        public async Task<bool> AddViewAsync(long userId, long postId)
        {
            try
            {
                var now = DateTime.Now;

                // 1. 设置10分钟限制标记（Redis SETEX，TTL 10分钟）
                var limitKey = GetViewLimitKey(userId, postId);
                await _redisService.SetAsync(limitKey, "1", VIEW_LIMIT_TTL);

                // 2. 更新Redis计数（立即）
                var countKey = GetViewCountKey(postId);
                var newCount = await _redisService.IncrementAsync(countKey);

                // 3. 写入待处理操作Hash（用于定时批量同步到数据库）
                var pendingField = GetPendingOperationField(userId, postId);
                var operation = new
                {
                    OccurredAt = now
                };
                var operationJson = JsonSerializer.Serialize(operation);
                await _redisService.HashSetAsync(VIEW_PENDING_OPERATIONS_KEY, pendingField, operationJson);

                _logger.LogInformation(
                    "[ViewService] 增加浏览次数操作成功。UserId: {UserId}, PostId: {PostId}, NewCount: {NewCount}",
                    userId, postId, newCount);

                return true;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "增加浏览次数操作失败。UserId: {UserId}, PostId: {PostId}",
                    userId, postId);
                throw;
            }
        }
    }
}