/// <summary>
/// Builds a <see cref="ServiceDescriptor"/>, describing a singleton <see cref="IHostedService"/>, to be used
/// with dependency injection.
/// </summary>
/// <remarks>
/// It reuses an existing <see cref="IBusProxy"/> singleton, if one is found using the provided
/// <see cref="IRabbitMqConfig.Id"/>.
///
/// If not, a new <see cref="IBusProxy"/> singleton is registered in the service factory wrapped by the
/// <see cref="ServiceDescriptor"/>.
/// </remarks>
public Func <IServiceProvider, T> Build(IServiceCollection serviceCollection)
{
var isConsumer = typeof(T).IsSubclassOf(typeof(RabbitMqConsumer <T>));
if (!isConsumer && !typeof(T).IsSubclassOf(typeof(RabbitMqProducer <T>)))
{
throw new Exception(
$"{nameof(T)}, of type {typeof(T).FullName}, must be a subclass of " +
$"{nameof(RabbitMqConsumer<T>)} or {nameof(RabbitMqProducer<T>)}.");
}
if (_configRabbitMqConfig == null)
{
_configRabbitMqConfig = new RabbitMqConfig();
}
var busProxy = serviceCollection
.Where(serviceDescriptor =>
serviceDescriptor.Lifetime == ServiceLifetime.Singleton &&
serviceDescriptor.ServiceType == typeof(IBusProxy))
.Select(serviceDescriptor => (IBusProxy)serviceDescriptor.ImplementationInstance)
.FirstOrDefault(registeredBusProxy => registeredBusProxy.Id == _configRabbitMqConfig.Id);
// ReSharper disable once ConditionIsAlwaysTrueOrFalse
// ReSharper disable HeuristicUnreachableCode
if (busProxy == null)
{
// build an IServiceProvider early so as to ensure that an ILogger<T> can be passed to
// ConsumerErrorStrategy
var serviceProvider =
new DefaultServiceProviderFactory(new ServiceProviderOptions
{
ValidateScopes = false
})
.CreateBuilder(serviceCollection)
.BuildServiceProvider();
var bus = RabbitMqService <T> .CreateLazyBus(
_configRabbitMqConfig, _configUseStronglyTypedMessages, _configUseCorrelationIds, serviceProvider);
busProxy = new BusProxy(_configRabbitMqConfig.Id, bus);
serviceCollection.AddSingleton(busProxy);
}
// ReSharper restore HeuristicUnreachableCode
Func <IServiceProvider, T> BuildServiceFactoryFactory()
{
T service = null;
var @lock = new object();
return(serviceProvider =>
{
// ReSharper disable once ConditionIsAlwaysTrueOrFalse
if (service != null)
{
return service;
}
lock (@lock)
{
if (service != null)
{
return service;
}
// _configRabbitMqConfig must not be null here
service = RabbitMqService <T> .Create <T>(
isConsumer, busProxy, _configRabbitMqConfig, _configOnConnected, serviceProvider);
return service;
}
});
}
return(BuildServiceFactoryFactory());
}