/// <summary>
/// Adds the ability for this graphql server to raise subscription events that can be published.
/// </summary>
/// <typeparam name="TSchema">The type of schema being configured.</typeparam>
/// <param name="schemaBuilder">The schema builder.</param>
/// <returns>GraphQL.AspNet.Interfaces.Configuration.ISchemaBuilder<TSchema>.</returns>
public static ISchemaBuilder <TSchema> AddSubscriptionPublishing <TSchema>(
this ISchemaBuilder <TSchema> schemaBuilder)
where TSchema : class, ISchema
{
var extension = new SubscriptionPublisherSchemaExtension <TSchema>();
// register the in-process publisher to the service collection before
// if one is not already registered
var defaultPublisher = CreateDefaultSubscriptionPublisherDescriptor();
extension.OptionalServices.Add(defaultPublisher);
// register the internal queueing mechanism that will asyncrounously transfer
// raised events from controller methods to the registered subscription publisher
schemaBuilder.AsServiceCollection().AddSingleton <SubscriptionEventQueue>();
schemaBuilder.AsServiceCollection().AddHostedService <SubscriptionPublicationService>();
schemaBuilder.AsServiceCollection().TryAdd(CreateDefaultSubscriptionRouterDescriptor());
schemaBuilder.Options.RegisterExtension(extension);
schemaBuilder.QueryExecutionPipeline.AddMiddleware <PublishRaisedSubscriptionEventsMiddleware <TSchema> >(
ServiceLifetime.Singleton);
return(schemaBuilder);
}