using QYZH.InteractiveMagazine.Infrastructure.RabbitMQ;

namespace QYZH.InteractiveMagazine.WorkService.Consumers;

/// <summary>
/// RabbitMQ 消费者后台服务，自动发现并启动所有已注册的 IQueueConsumer
/// </summary>
public class RabbitMQHostedService : BackgroundService
{
    private readonly IServiceProvider _serviceProvider;
    private readonly ILogger<RabbitMQHostedService> _logger;

    public RabbitMQHostedService(IServiceProvider serviceProvider, ILogger<RabbitMQHostedService> logger)
    {
        _serviceProvider = serviceProvider;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        using var scope = _serviceProvider.CreateScope();
        var consumers = scope.ServiceProvider.GetServices<IQueueConsumer>().ToList();

        if (consumers.Count == 0)
        {
            _logger.LogWarning("未注册任何队列消费者");
            return;
        }

        _logger.LogInformation("发现 {Count} 个队列消费者，开始启动...", consumers.Count);

        var tasks = consumers.Select(c => StartConsumerAsync(c, stoppingToken)).ToList();
        await Task.WhenAll(tasks);
    }

    private async Task StartConsumerAsync(IQueueConsumer queueConsumer, CancellationToken stoppingToken)
    {
        var queueName = queueConsumer.QueueName;
        var exchange = queueConsumer.Exchange;
        var routingKey = queueConsumer.RoutingKey;
        _logger.LogInformation("正在启动消费者: {QueueName}, Exchange: {Exchange}, RoutingKey: {RoutingKey}", queueName, exchange, routingKey);

        try
        {
            var rabbitMQService = _serviceProvider.GetRequiredService<IRabbitMQService>();

            await rabbitMQService.ReceiveAsync(exchange, queueName, routingKey, async (channel, ea) =>
            {
                // 声明死信队列及绑定（幂等操作，确保DLQ存在）
                var dlqName = $"{queueName}.dlq";
                var dlqRoutingKey = $"{routingKey}.dlq";
                await channel.QueueDeclareAsync(queue: dlqName, durable: true, exclusive: false, autoDelete: false, arguments: null);
                await channel.QueueBindAsync(queue: dlqName, exchange: exchange, routingKey: dlqRoutingKey, arguments: null);

                // 每条消息创建独立 scope，确保消费者内可注入 Scoped 服务
                using var messageScope = _serviceProvider.CreateScope();
                var consumer = messageScope.ServiceProvider
                    .GetServices<IQueueConsumer>()
                    .First(c => c.QueueName == queueName);

                try
                {
                    await consumer.HandleAsync(ea.Body.ToArray(), stoppingToken);
                    await channel.BasicAckAsync(ea.DeliveryTag, false, stoppingToken);
                }
                catch (Exception ex)
                {
                    _logger.LogError(ex, "消费者 {QueueName} 处理消息异常", queueName);

                    // 发送到死信队列，成功则从主队列移除，失败则重新入队
                    var dlqSent = await SendToDeadLetterQueueAsync(exchange, dlqName, dlqRoutingKey, queueName, ea.Body.ToArray(), ex, stoppingToken);
                    await channel.BasicNackAsync(ea.DeliveryTag, false, !dlqSent, stoppingToken);

                    if (dlqSent)
                    {
                        _logger.LogInformation("消息已转入死信队列 {DlqName}", dlqName);
                    }

                    try
                    {
                        await consumer.OnErrorAsync(ea.Body.ToArray(), ex);
                    }
                    catch (Exception errorEx)
                    {
                        _logger.LogError(errorEx, "消费者 {QueueName} OnErrorAsync 执行异常", queueName);
                    }
                }
            }, stoppingToken);
        }
        catch (OperationCanceledException)
        {
            _logger.LogInformation("消费者 {QueueName} 已停止", queueName);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "消费者 {QueueName} 启动失败", queueName);
        }
    }

    /// <summary>
    /// 将失败消息发送到死信队列
    /// </summary>
    private async Task<bool> SendToDeadLetterQueueAsync(string exchange, string dlqName, string dlqRoutingKey, string originalQueueName, byte[] body, Exception exception, CancellationToken cancellationToken)
    {
        try
        {
            var rabbitMQConnection = _serviceProvider.GetRequiredService<IRabbitMQConnection>();
            using var channel = await rabbitMQConnection.CreateChannel();
            await channel.QueueDeclareAsync(queue: dlqName, durable: true, exclusive: false, autoDelete: false, arguments: null);
            await channel.QueueBindAsync(queue: dlqName, exchange: exchange, routingKey: dlqRoutingKey, arguments: null);

            var properties = new RabbitMQ.Client.BasicProperties
            {
                Persistent = true,
                Headers = new Dictionary<string, object?>
                {
                    ["x-original-queue"] = originalQueueName,
                    ["x-error-type"] = exception.GetType().FullName,
                    ["x-error-message"] = exception.Message,
                    ["x-failed-at"] = DateTimeOffset.UtcNow.ToString("O")
                }
            };
            await channel.BasicPublishAsync(exchange, dlqRoutingKey, false, properties, body, cancellationToken);

            _logger.LogInformation("消息已发送到死信队列: {DlqName}", dlqName);
            return true;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "发送消息到死信队列 {DlqName} 失败", dlqName);
            return false;
        }
    }
}