Error Handling

using GenHTTP.Engine.Internal;

using GenHTTP.Api.Content;
using GenHTTP.Api.Protocol;

using GenHTTP.Modules.ErrorHandling;
using GenHTTP.Modules.Functional;
using GenHTTP.Modules.IO;
using GenHTTP.Modules.Layouting;
using GenHTTP.Modules.Practices;

var orders = Inline.Create()
                   // GET /api/orders/42 answers 404 as JSON
                   .Get(":id", (int id) => (id == 1) ? new Order(1, "Coffee") : throw new ProviderException(ResponseStatus.NotFound, $"There is no order with id {id}"))
                   // POST /api/orders/ answers 409 via the mapper below
                   .Post((Order order) => Shop.PlaceOrder(order))
                   .Add(ErrorHandler.From(new OutOfStockMapper()));

var website = Layout.Create()
                    .Index(Content.From(Resource.FromString("<h1>Welcome to our shop!</h1>").Type(ContentType.TextHtml)))
                    .Add(ErrorHandler.Html()); // GET /does-not-exist answers 404 as HTML page

var app = Layout.Create()
                .Add("api/orders", orders)
                .Add(website);

await Host.Create()
          .Handler(app)
          .Defaults()
          .RunAsync();

public record Order(int Id, string Product);

public class OutOfStockException(string product) : Exception($"Sorry, '{product}' is sold out")
{

    public string Product => product;

}

public static class Shop
{

    public static Order PlaceOrder(Order order) => throw new OutOfStockException(order.Product);

}

public class OutOfStockMapper : IErrorMapper<OutOfStockException>
{

    public ValueTask<IResponse?> Map(IRequest request, IHandler handler, OutOfStockException error, ByteString? acceptedFormat)
    {
        var response = request.Respond()
                              .Status(ResponseStatus.Conflict)
                              .Content(error.Message, ContentType.TextPlain)
                              .Build();

        return new(response);
    }

    // null passes the request on, so the default error handling renders the 404
    public ValueTask<IResponse?> GetNotFound(IRequest request, IHandler handler, ByteString? acceptedFormat) => new();

}