formatter.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Formatters;
using Microsoft.Net.Http.Headers;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;

namespace Hangman.Api.Siren.Formatters
{
    public class SirenOutputFormatter : TextOutputFormatter
    {
        private static readonly JsonSerializerSettings DefaultJsonSerializerSettings 
            = new JsonSerializerSettings
        {
            ContractResolver = new CamelCasePropertyNamesContractResolver(),
            NullValueHandling = NullValueHandling.Ignore,
        };

        private static readonly Encoding DefaultEncoding = Encoding.UTF8;

        private readonly Dictionary<Type, object> _templates;
        private readonly JsonSerializerSettings _jsonSerializerSettings;

        public SirenOutputFormatter(Dictionary<Type, object> templates) 
            : this(templates, DefaultJsonSerializerSettings, DefaultEncoding)
        {

        }

        public SirenOutputFormatter(Dictionary<Type, object> templates, JsonSerializerSettings settings) 
            : this(templates, settings, DefaultEncoding)
        {
        }

        public SirenOutputFormatter(Dictionary<Type, object> templates, Encoding encoding) 
            : this(templates, DefaultJsonSerializerSettings, encoding)
        {
        }

        public SirenOutputFormatter(Dictionary<Type, object> templates, JsonSerializerSettings settings, Encoding encoding)
        {
            _templates = templates;
            _jsonSerializerSettings = settings;
            SupportedMediaTypes.Add(MediaTypeHeaderValue.Parse("application/vnd.siren+json"));
            SupportedEncodings.Add(encoding);
        }

        protected override bool CanWriteType(Type type)
        {
            return _templates.ContainsKey(type);
        }

        public override Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
        {
            var template = _templates[context.ObjectType];
            var builder = template.GetType()
                .GetMethod("ToRepresentation")
                .Invoke(template, new [] {context.Object});

            var entity = builder.GetType().GetMethod("Build").Invoke(builder, new object[0]);

            return context.HttpContext.Response.WriteAsync(
                JsonConvert.SerializeObject(entity, _jsonSerializerSettings),
                selectedEncoding,
                context.HttpContext.RequestAborted);
        }
    }
}