.Net Core use new ApplicationBuilder instead of IApplicationBuilder from configure - asp.net-core

Question

I am attempting to create a "registry" so that just creating a new class implementing IServiceCollectionInitializer or IApplicationBuilderInitializer allows it to be loaded. Instead of having a giant start up class the registry would add those automatically.
My problem is I dont know how to make the app either use a new application builder or retrieve the the one given automatically without getting it from startup.
public class ServiceCollectionInitializerRegistry
{
private readonly IList<IServiceCollectionInitializer> _serviceCollectionInitializers;
private readonly IServiceCollection _serviceCollection;
private readonly IServiceProvider _serviceProvider;
public ServiceCollectionInitializerRegistry(IServiceCollection serviceCollection)
{
_serviceCollectionInitializers = new List<IServiceCollectionInitializer>();
_serviceCollection = serviceCollection;
_serviceProvider = serviceCollection.BuildServiceProvider();
}
public ServiceCollectionInitializerRegistry WithInitializers(
params IServiceCollectionInitializer[] initializers)
{
if (!initializers.Any())
{
return this;
}
foreach (var initializer in initializers)
{
_serviceCollectionInitializers.Add(initializer);
}
return this;
}
public ServiceCollectionInitializerRegistry WithAssemblyInitializers()
{
var assembly = Assembly.GetEntryAssembly();
var initializerTypes =
assembly.GetTypes()
.Where(type => typeof(IServiceCollectionInitializer).IsAssignableFrom(type));
if (!initializerTypes.Any())
{
return this;
}
foreach (var type in initializerTypes)
{
_serviceCollectionInitializers.Add((IServiceCollectionInitializer)Activator.CreateInstance(type));
}
return this;
}
public void Build()
{
var configuration = _serviceProvider.GetRequiredService<IConfiguration>();
foreach (var serviceCollectionInitializer in _serviceCollectionInitializers)
{
var logger = _serviceProvider.GetRequiredService<ILoggerProvider>()
.CreateLogger(serviceCollectionInitializer.GetType().AssemblyQualifiedName);
serviceCollectionInitializer
.Initialize(
configuration,
_serviceCollection, logger);
}
}
}
public class ExceptionHandlingInitializer : IServiceCollectionInitializer, IApplicationBuilderInitializer
{
public void Initialize(IConfiguration configuration, IServiceCollection services, ILogger logger)
{
services.AddSingleton<IExceptionMapper, ExceptionMapper>();
services.AddSingleton<IExceptionHandler, ExceptionHandler>();
}
public void Initialize(IConfiguration configuration, IApplicationBuilder builder, ILoggerFactory loggerFactory)
{
builder.UseExceptionHandlerMiddleware();
}
}