A NancyFx IResponseFormatter extension to do content-negotiation

CustomFormatterExtensions.cs

using System;
using System.Linq;
using Nancy.ViewEngines;

namespace Nancy
{
    public static class CustomFormatterExtensions
    {
        public static Response AsNegotiated<TModel>(this IResponseFormatter formatter, TModel model, HttpStatusCode statusCode = HttpStatusCode.OK, Tuple<Func<Response>, string> defaultResponse = null)
        {

            if (defaultResponse == null)
                defaultResponse = new Tuple<Func<Response>, string>(() => new Response
                    {
                        ContentType = null,
                        StatusCode = HttpStatusCode.UnsupportedMediaType
                    }, null);

            var defaultResponseDelegate = defaultResponse.Item1;
            var defaultContentType = defaultResponse.Item2;

            if (formatter.Context.Request == null || formatter.Context.Request.Headers == null || formatter.Context.Request.Headers.Accept == null)
                return defaultResponseDelegate.Invoke();

            var accept = formatter.Context.Request.Headers.Accept;
            var weightedContentTypes = accept.Select(x => x.Item1).DefaultIfEmpty();

            foreach (var contentType in weightedContentTypes)
            {
                if (defaultContentType == contentType || contentType == "*/*") return defaultResponseDelegate.Invoke();

                var serializer = formatter.Serializers.FirstOrDefault(x => x.CanSerialize(contentType));
                if (serializer != null && !(contentType.EndsWith("xml") && model.IsAnonymousType()))
                {
                    return new Response
                        {
                            Contents = stream => serializer.Serialize(contentType, model, stream),
                            ContentType = contentType,
                            StatusCode = statusCode
                        };
                }
            }
            return defaultResponseDelegate.Invoke();
        }

    }
}

/* Usage:

        public AsNegotiatedTestModule() : base("/negotiated")
        {
            Get["/view"] = p =>
                {
                    var model = new Person("John", "Doe");
                    return Response.AsNegotiated(model, defaultResponse: new Tuple<Func<Response>, string>(()=>View[model],"text/html"));
                };
        }

    Request to '/negotiated/view' with this header returns the View (html):
        Accept: text/html,application/json;q=0.9,application/xml;q=0.8


    Request to '/negotiated/view' with this header returns JSON:
        Accept: text/html;q=0.7,application/json;q=0.9,application/xml;q=0.8


*/