live-forum/server/webapi/LiveForum/LiveForum.WebApi/BackgroundServices/LikeMessageConsumer.cs

using LiveForum.IService.Messages;
using LiveForum.Model.Events;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using StackExchange.Redis;
using System;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;

namespace LiveForum.WebApi.BackgroundServices
{
    /// <summary>
    /// 点赞消息后台消费者
    /// 从 message:events:like 队列消费点赞事件
    /// </summary>
    public class LikeMessageConsumer : BackgroundService
    {
        private readonly IDatabase _database;
        private readonly IMessageEventHandler _eventHandler;
        private readonly ILogger<LikeMessageConsumer> _logger;
        private const string QUEUE_NAME = "message:events:like";

        public LikeMessageConsumer(
            IDatabase database,
            IMessageEventHandler eventHandler,
            ILogger<LikeMessageConsumer> logger)
        {
            _database = database;
            _eventHandler = eventHandler;
            _logger = logger;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            _logger.LogInformation("[LikeConsumer] 点赞消息消费者已启动");

            while (!stoppingToken.IsCancellationRequested)
            {
                try
                {
                    // 从Redis List左侧阻塞弹出（BLPOP，超时1秒）
                    var result = await _database.ListLeftPopAsync(QUEUE_NAME);

                    if (result.HasValue)
                    {
                        var json = result.ToString();
                        
                        // 反序列化事件
                        var evt = JsonSerializer.Deserialize<LikeEvent>(json, new JsonSerializerOptions
                        {
                            PropertyNameCaseInsensitive = true
                        });

                        if (evt != null)
                        {
                            _logger.LogDebug(
                                "[LikeConsumer] 开始处理点赞事件: EventId={EventId}, ContentType={ContentType}, ContentId={ContentId}",
                                evt.EventId, evt.ContentType, evt.ContentId);

                            // 处理事件（带重试）
                            await ProcessWithRetryAsync(evt, stoppingToken);
                        }
                    }
                    else
                    {
                        // 队列为空，等待500毫秒再查询（减少CPU占用）
                        await Task.Delay(500, stoppingToken);
                    }
                }
                catch (OperationCanceledException)
                {
                    // 正常停止
                    break;
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "[LikeConsumer] 消费点赞事件时发生异常");
                    
                    // 发生异常后等待5秒再继续
                    await Task.Delay(5000, stoppingToken);
                }
            }

            _logger.LogInformation("[LikeConsumer] 点赞消息消费者已停止");
        }

        /// <summary>
        /// 带重试的事件处理
        /// </summary>
        private async Task ProcessWithRetryAsync(LikeEvent evt, CancellationToken stoppingToken)
        {
            const int maxRetries = 3;
            var retryCount = 0;

            while (retryCount < maxRetries && !stoppingToken.IsCancellationRequested)
            {
                try
                {
                    await _eventHandler.HandleLikeEventAsync(evt);
                    
                    _logger.LogDebug(
                        "[LikeConsumer] 点赞事件处理成功: EventId={EventId}",
                        evt.EventId);
                    
                    return; // 成功，退出重试循环
                }
                catch (Exception ex)
                {
                    retryCount++;
                    
                    if (retryCount >= maxRetries)
                    {
                        _logger.LogError(ex,
                            "[LikeConsumer] 点赞事件处理失败（已重试{RetryCount}次）: EventId={EventId}",
                            retryCount, evt.EventId);
                        
                        // TODO: 可以将失败的事件写入死信队列或日志表
                        return;
                    }

                    _logger.LogWarning(ex,
                        "[LikeConsumer] 点赞事件处理失败，准备重试({RetryCount}/{MaxRetries}): EventId={EventId}",
                        retryCount, maxRetries, evt.EventId);

                    // 延迟后重试（指数退避）
                    await Task.Delay(1000 * retryCount, stoppingToken);
                }
            }
        }

        public override Task StopAsync(CancellationToken cancellationToken)
        {
            _logger.LogInformation("[LikeConsumer] 正在停止点赞消息消费者...");
            return base.StopAsync(cancellationToken);
        }
    }
}