eShopOnContainers/src/BuildingBlocks/EventBus/EventBusServiceBus/EventBusServiceBus.cs

namespace Microsoft.eShopOnContainers.BuildingBlocks.EventBusServiceBus
{
    using Autofac;
    using Microsoft.Azure.ServiceBus;
    using Microsoft.eShopOnContainers.BuildingBlocks.EventBus;
    using Microsoft.eShopOnContainers.BuildingBlocks.EventBus.Abstractions;
    using Microsoft.eShopOnContainers.BuildingBlocks.EventBus.Events;
    using Microsoft.Extensions.Logging;   
    using System;
    using System.Text;
    using System.Text.Json;
    using System.Threading.Tasks;

    public class EventBusServiceBus : IEventBus
    {
        private readonly IServiceBusPersisterConnection _serviceBusPersisterConnection;
        private readonly ILogger<EventBusServiceBus> _logger;
        private readonly IEventBusSubscriptionsManager _subsManager;
        private readonly ILifetimeScope _autofac;
        private readonly string AUTOFAC_SCOPE_NAME = "eshop_event_bus";
        private const string INTEGRATION_EVENT_SUFFIX = "IntegrationEvent";

        public EventBusServiceBus(IServiceBusPersisterConnection serviceBusPersisterConnection,
            ILogger<EventBusServiceBus> logger, IEventBusSubscriptionsManager subsManager, ILifetimeScope autofac)
        {
            _serviceBusPersisterConnection = serviceBusPersisterConnection;
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _subsManager = subsManager ?? new InMemoryEventBusSubscriptionsManager();
            _autofac = autofac;

            RemoveDefaultRule();
            RegisterSubscriptionClientMessageHandler();
        }

        public void Publish(IntegrationEvent @event)
        {
            var eventName = @event.GetType().Name.Replace(INTEGRATION_EVENT_SUFFIX, "");
            var jsonMessage = JsonSerializer.Serialize(@event);
            var body = Encoding.UTF8.GetBytes(jsonMessage);

            var message = new Message
            {
                MessageId = Guid.NewGuid().ToString(),
                Body = body,
                Label = eventName,
            };

            _serviceBusPersisterConnection.TopicClient.SendAsync(message)
                .GetAwaiter()
                .GetResult();
        }

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

            _subsManager.AddDynamicSubscription<TH>(eventName);
        }

        public void Subscribe<T, TH>()
            where T : IntegrationEvent
            where TH : IIntegrationEventHandler<T>
        {
            var eventName = typeof(T).Name.Replace(INTEGRATION_EVENT_SUFFIX, "");

            var containsKey = _subsManager.HasSubscriptionsForEvent<T>();
            if (!containsKey)
            {
                try
                {
                    _serviceBusPersisterConnection.SubscriptionClient.AddRuleAsync(new RuleDescription
                    {
                        Filter = new CorrelationFilter { Label = eventName },
                        Name = eventName
                    }).GetAwaiter().GetResult();
                }
                catch (ServiceBusException)
                {
                    _logger.LogWarning("The messaging entity {eventName} already exists.", eventName);
                }
            }

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

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

        public void Unsubscribe<T, TH>()
            where T : IntegrationEvent
            where TH : IIntegrationEventHandler<T>
        {
            var eventName = typeof(T).Name.Replace(INTEGRATION_EVENT_SUFFIX, "");

            try
            {
                _serviceBusPersisterConnection
                    .SubscriptionClient
                    .RemoveRuleAsync(eventName)
                    .GetAwaiter()
                    .GetResult();
            }
            catch (MessagingEntityNotFoundException)
            {
                _logger.LogWarning("The messaging entity {eventName} Could not be found.", eventName);
            }

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

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

        public void UnsubscribeDynamic<TH>(string eventName)
            where TH : IDynamicIntegrationEventHandler
        {
            _logger.LogInformation("Unsubscribing from dynamic event {EventName}", eventName);

            _subsManager.RemoveDynamicSubscription<TH>(eventName);
        }

        public void Dispose()
        {
            _subsManager.Clear();
        }

        private void RegisterSubscriptionClientMessageHandler()
        {
            _serviceBusPersisterConnection.SubscriptionClient.RegisterMessageHandler(
                async (message, token) =>
                {
                    var eventName = $"{message.Label}{INTEGRATION_EVENT_SUFFIX}";
                    var messageData = Encoding.UTF8.GetString(message.Body);

                    // Complete the message so that it is not received again.
                    if (await ProcessEvent(eventName, messageData))
                    {
                        await _serviceBusPersisterConnection.SubscriptionClient.CompleteAsync(message.SystemProperties.LockToken);
                    }
                },
                new MessageHandlerOptions(ExceptionReceivedHandler) { MaxConcurrentCalls = 10, AutoComplete = false });
        }

        private Task ExceptionReceivedHandler(ExceptionReceivedEventArgs exceptionReceivedEventArgs)
        {
            var ex = exceptionReceivedEventArgs.Exception;
            var context = exceptionReceivedEventArgs.ExceptionReceivedContext;

            _logger.LogError(ex, "ERROR handling message: {ExceptionMessage} - Context: {@ExceptionContext}", ex.Message, context);

            return Task.CompletedTask;
        }

        private async Task<bool> ProcessEvent(string eventName, string message)
        {
            var processed = false;
            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 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);
                            var concreteType = typeof(IIntegrationEventHandler<>).MakeGenericType(eventType);
                            await (Task)concreteType.GetMethod("Handle").Invoke(handler, new object[] { integrationEvent });
                        }
                    }
                }
                processed = true;
            }
            return processed;
        }

        private void RemoveDefaultRule()
        {
            try
            {
                _serviceBusPersisterConnection
                    .SubscriptionClient
                    .RemoveRuleAsync(RuleDescription.DefaultRuleName)
                    .GetAwaiter()
                    .GetResult();
            }
            catch (MessagingEntityNotFoundException)
            {
                _logger.LogWarning("The messaging entity {DefaultRuleName} Could not be found.", RuleDescription.DefaultRuleName);
            }
        }
    }
}