eShopOnContainers/src/BuildingBlocks/EventBus/EventBusRabbitMQ/EventBusRabbitMQ.cs

namespace Microsoft.eShopOnContainers.BuildingBlocks.EventBusRabbitMQ;

public class EventBusRabbitMQ : IEventBus, IDisposable
{
    const string BROKER_NAME = "eshop_event_bus";
    const string AUTOFAC_SCOPE_NAME = "eshop_event_bus";

    private readonly IRabbitMQPersistentConnection _persistentConnection;
    private readonly ILogger<EventBusRabbitMQ> _logger;
    private readonly IEventBusSubscriptionsManager _subsManager;
    private readonly ILifetimeScope _autofac;
    private readonly int _retryCount;

    private IModel _consumerChannel;
    private string _queueName;

    public EventBusRabbitMQ(IRabbitMQPersistentConnection persistentConnection, ILogger<EventBusRabbitMQ> logger,
        ILifetimeScope autofac, IEventBusSubscriptionsManager subsManager, string queueName = null, int retryCount = 5)
    {
        _persistentConnection = persistentConnection ?? throw new ArgumentNullException(nameof(persistentConnection));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _subsManager = subsManager ?? new InMemoryEventBusSubscriptionsManager();
        _queueName = queueName;
        _consumerChannel = CreateConsumerChannel();
        _autofac = autofac;
        _retryCount = retryCount;
        _subsManager.OnEventRemoved += SubsManager_OnEventRemoved;
    }

    private void SubsManager_OnEventRemoved(object sender, string eventName)
    {
        if (!_persistentConnection.IsConnected)
        {
            _persistentConnection.TryConnect();
        }

        using (var channel = _persistentConnection.CreateModel())
        {
            channel.QueueUnbind(queue: _queueName,
                exchange: BROKER_NAME,
                routingKey: eventName);

            if (_subsManager.IsEmpty)
            {
                _queueName = string.Empty;
                _consumerChannel.Close();
            }
        }
    }

    public void Publish(IntegrationEvent @event)
    {
        if (!_persistentConnection.IsConnected)
        {
            _persistentConnection.TryConnect();
        }

        var policy = RetryPolicy.Handle<BrokerUnreachableException>()
            .Or<SocketException>()
            .WaitAndRetry(_retryCount, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (ex, time) =>
            {
                _logger.LogWarning(ex, "Could not publish event: {EventId} after {Timeout}s ({ExceptionMessage})", @event.Id, $"{time.TotalSeconds:n1}", ex.Message);
            });

        var eventName = @event.GetType().Name;

        _logger.LogTrace("Creating RabbitMQ channel to publish event: {EventId} ({EventName})", @event.Id, eventName);

        using (var channel = _persistentConnection.CreateModel())
        {
            _logger.LogTrace("Declaring RabbitMQ exchange to publish event: {EventId}", @event.Id);

            channel.ExchangeDeclare(exchange: BROKER_NAME, type: "direct");
                                
            var body = JsonSerializer.SerializeToUtf8Bytes(@event, @event.GetType(), new JsonSerializerOptions
            {
                WriteIndented = true
            });

            policy.Execute(() =>
            {
                var properties = channel.CreateBasicProperties();
                properties.DeliveryMode = 2; // persistent

                _logger.LogTrace("Publishing event to RabbitMQ: {EventId}", @event.Id);

                channel.BasicPublish(
                    exchange: BROKER_NAME,
                    routingKey: eventName,
                    mandatory: true,
                    basicProperties: properties,
                    body: body);
            });
        }
    }

    public void SubscribeDynamic<TH>(string eventName)
        where TH : IDynamicIntegrationEventHandler
    {
        _logger.LogInformation("Subscribing to dynamic event {EventName} with {EventHandler}", eventName, typeof(TH).GetGenericTypeName());

        DoInternalSubscription(eventName);
        _subsManager.AddDynamicSubscription<TH>(eventName);
        StartBasicConsume();
    }

    public void Subscribe<T, TH>()
        where T : IntegrationEvent
        where TH : IIntegrationEventHandler<T>
    {
        var eventName = _subsManager.GetEventKey<T>();
        DoInternalSubscription(eventName);

        _logger.LogInformation("Subscribing to event {EventName} with {EventHandler}", eventName, typeof(TH).GetGenericTypeName());

        _subsManager.AddSubscription<T, TH>();
        StartBasicConsume();
    }

    private void DoInternalSubscription(string eventName)
    {
        var containsKey = _subsManager.HasSubscriptionsForEvent(eventName);
        if (!containsKey)
        {
            if (!_persistentConnection.IsConnected)
            {
                _persistentConnection.TryConnect();
            }
 
            _consumerChannel.QueueBind(queue: _queueName,
                                exchange: BROKER_NAME,
                                routingKey: eventName);
        }
    }

    public void Unsubscribe<T, TH>()
        where T : IntegrationEvent
        where TH : IIntegrationEventHandler<T>
    {
        var eventName = _subsManager.GetEventKey<T>();

        _logger.LogInformation("Unsubscribing from event {EventName}", eventName);

        _subsManager.RemoveSubscription<T, TH>();
    }

    public void UnsubscribeDynamic<TH>(string eventName)
        where TH : IDynamicIntegrationEventHandler
    {
        _subsManager.RemoveDynamicSubscription<TH>(eventName);
    }

    public void Dispose()
    {
        if (_consumerChannel != null)
        {
            _consumerChannel.Dispose();
        }

        _subsManager.Clear();
    }

    private void StartBasicConsume()
    {
        _logger.LogTrace("Starting RabbitMQ basic consume");

        if (_consumerChannel != null)
        {
            var consumer = new AsyncEventingBasicConsumer(_consumerChannel);

            consumer.Received += Consumer_Received;

            _consumerChannel.BasicConsume(
                queue: _queueName,
                autoAck: false,
                consumer: consumer);
        }
        else
        {
            _logger.LogError("StartBasicConsume can't call on _consumerChannel == null");
        }
    }

    private async Task Consumer_Received(object sender, BasicDeliverEventArgs eventArgs)
    {
        var eventName = eventArgs.RoutingKey;
        var message = Encoding.UTF8.GetString(eventArgs.Body.Span);

        try
        {
            if (message.ToLowerInvariant().Contains("throw-fake-exception"))
            {
                throw new InvalidOperationException($"Fake exception requested: \"{message}\"");
            }

            await ProcessEvent(eventName, message);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "----- ERROR Processing message \"{Message}\"", message);
        }

        // Even on exception we take the message off the queue.
        // in a REAL WORLD app this should be handled with a Dead Letter Exchange (DLX). 
        // For more information see: https://www.rabbitmq.com/dlx.html
        _consumerChannel.BasicAck(eventArgs.DeliveryTag, multiple: false);
    }

    private IModel CreateConsumerChannel()
    {
        if (!_persistentConnection.IsConnected)
        {
            _persistentConnection.TryConnect();
        }

        _logger.LogTrace("Creating RabbitMQ consumer channel");

        var channel = _persistentConnection.CreateModel();

        channel.ExchangeDeclare(exchange: BROKER_NAME,
                                type: "direct");

        channel.QueueDeclare(queue: _queueName,
                                durable: true,
                                exclusive: false,
                                autoDelete: false,
                                arguments: null);

        channel.CallbackException += (sender, ea) =>
        {
            _logger.LogWarning(ea.Exception, "Recreating RabbitMQ consumer channel");

            _consumerChannel.Dispose();
            _consumerChannel = CreateConsumerChannel();
            StartBasicConsume();
        };

        return channel;
    }

    private async Task ProcessEvent(string eventName, string message)
    {
        _logger.LogTrace("Processing RabbitMQ event: {EventName}", eventName);

        if (_subsManager.HasSubscriptionsForEvent(eventName))
        {
            using (var scope = _autofac.BeginLifetimeScope(AUTOFAC_SCOPE_NAME))
            {
                var subscriptions = _subsManager.GetHandlersForEvent(eventName);
                foreach (var subscription in subscriptions)
                {
                    if (subscription.IsDynamic)
                    {
                        var handler = scope.ResolveOptional(subscription.HandlerType) as IDynamicIntegrationEventHandler;
                        if (handler == null) continue;
                        using dynamic eventData = JsonDocument.Parse(message);                            
                        await Task.Yield();
                        await handler.Handle(eventData);
                    }
                    else
                    {
                        var handler = scope.ResolveOptional(subscription.HandlerType);
                        if (handler == null) continue;
                        var eventType = _subsManager.GetEventTypeByName(eventName);
                        var integrationEvent = JsonSerializer.Deserialize(message, eventType, new JsonSerializerOptions() { PropertyNameCaseInsensitive= true});                            
                        var concreteType = typeof(IIntegrationEventHandler<>).MakeGenericType(eventType);

                        await Task.Yield();
                        await (Task)concreteType.GetMethod("Handle").Invoke(handler, new object[] { integrationEvent });
                    }
                }
            }
        }
        else
        {
            _logger.LogWarning("No subscription for RabbitMQ event: {EventName}", eventName);
        }
    }
}