RunnersMeet/src/RunnersMeet.Server/RequestHandlerModule.cs

using System.Reflection;

namespace RunnersMeet.Server;

public class RequestHandlerModule : IAppConfigurationModule
{
	public void ConfigureServices(IServiceCollection services, IConfigurationRoot config)
	{
		services.AddScoped<IRequestRouter, RequestRouter>();

		Register(services, new List<HandlerMatcher>
		{
			// More specific first, then fall back to more general
			new HandlerMatcher(typeof(IRequestHandler<,,>)),
			new HandlerMatcher(typeof(IRequestHandler<,>)),
		});
	}

	public void ConfigureApplication(WebApplication app)
	{
	}

	private void Register(IServiceCollection services, IList<HandlerMatcher> matchers)
	{
		foreach (var candidate in Assembly.GetExecutingAssembly().GetTypes().Where(t => t.IsClass))
		{
			var matcher = matchers.FirstOrDefault(m => m.IsMatch(candidate));
			if (matcher != null)
			{
				foreach (var handlerInterface in matcher.GetHandlerInterfaces(candidate))
				{
					services.AddScoped(handlerInterface, candidate);
				}
			}
		}
	}

	private sealed class HandlerMatcher
	{
		private readonly Type _genericInterfaceType;

		public HandlerMatcher(Type genericInterfaceType)
		{
			_genericInterfaceType = genericInterfaceType;
		}

		public bool IsMatch(Type t) => t.GetInterfaces().Any(i => ImplementsExactly(i, _genericInterfaceType));

		public IEnumerable<Type> GetHandlerInterfaces(Type t) => t.GetInterfaces().Where(i => ImplementsExactly(i, _genericInterfaceType));

		private static bool ImplementsExactly(Type candidate, Type genericInterface)
		{
			if (!candidate.IsGenericType)
			{
				return false;
			}

			var genericTypeDefinition = candidate.GetGenericTypeDefinition();
			return /*genericTypeDefinition.GenericTypeArguments.Length == genericInterface.GenericTypeArguments.Length
			       &&*/ genericTypeDefinition == genericInterface;
		}
	}
}