LightEndpoints

Program.cs

using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddKeyedSingleton<Counter>("sng");
builder.Services.AddKeyedScoped<Counter>("scp");
builder.Services.AddScoped<EndpointAsAClass>();
builder.Services.AddScoped<EndpointWithARequest>();

var app = builder.Build();
app.MapEndpoint<EndpointAsAClass>("/");
app.MapEndpoint<EndpointWithARequest, string>("/{req}");

app.Run();

public interface IEndpoint
{
    Task<IResult> RunAsync() => Task.FromResult<IResult>(TypedResults.Ok());
}

public interface IEndpoint<TRequest> : IEndpoint
{
    Task<IResult> RunAsync(TRequest request);
}

public static class Mapper
{
    public static void MapEndpoint<TEndpoint>(this WebApplication app, string pattern, string? method = default)
        where TEndpoint : IEndpoint =>
            app.MapMethods(pattern, [ method ?? HttpMethods.Get ], async (TEndpoint ep) => await ep.RunAsync());
    
    public static void MapEndpoint<TEndpoint, TRequest>(this WebApplication app, string pattern, string? method = default)
        where TEndpoint : IEndpoint<TRequest> =>
            app.MapMethods(pattern, [ method ?? HttpMethods.Get ], async (TRequest req, [FromServices]TEndpoint ep) => await ep.RunAsync(req));
}

public class Counter
{
    private int Count { get; set; }
    public string County() => $"Count: {++Count}";
}

public class EndpointAsAClass([FromKeyedServices("sng")]Counter sng, [FromKeyedServices("scp")]Counter scp) : IEndpoint
{
    public async Task<IResult> RunAsync()
    {
        return TypedResults.Ok($"Hello. Singleton: {sng.County()}. Scoped: {scp.County()}");
    }
}

public class EndpointWithARequest : IEndpoint<string>
{
    public async Task<IResult> RunAsync(string req)
    {
        return TypedResults.Ok($"Hello, {req}");
    }
}