API/TOOHUCardAPI/Controllers/MethodBasedController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using TOOHUCardAPI.Data;
using TOOHUCardAPI.Data.Services;
using MethodMap = System.Collections.Generic.Dictionary<string, System.Reflection.MethodInfo>;
namespace TOOHUCardAPI.Controllers
{
    public class MethodBasedController<TChildType> : ControllerBase
    {
        public delegate Task<IActionResult> EndpointHandler(string requestBody);

        /**
         * The game uses a single endpoint for player data.
         * The object they send has a method field that's used to decide what's being done
         * So let's use a single entry point and redirect based on that
         */
        [HttpPost]
        public async Task<IActionResult> EntryPoint([FromBody] object bodyObj)
        {
            string body = JsonConvert.SerializeObject(bodyObj);
            JObject request = JObject.Parse(body);
            string method = request["method"].ToString();
            try
            {
                return await InvokeEndpointHandlerForMethod<TChildType>(this, method, body);
            }
            catch (TooHooException e)
            {
                return Ok(e.response);
            }
        }

        private Task<IActionResult> InvokeEndpointHandlerForMethod<T>(object _this, string method, string body)
        {
            MethodMap registeredEndpointHandlers = GetMethodMapForType<T>();
            if (registeredEndpointHandlers.ContainsKey(method))
            {
                return ((EndpointHandler) registeredEndpointHandlers[method]
                    .CreateDelegate(typeof(EndpointHandler), _this))(body);
            }
            throw new MissingEndpointHandlerException(method);
        }

        private MethodMap GetMethodMapForType<T>()
        {
            var methodMapByType = MethodMapService.MethodMapByType;
            if (!methodMapByType.ContainsKey(typeof(T)))
            {
                methodMapByType[typeof(T)] = RegisterEndpointHandlers<T>();
            }
            return methodMapByType[typeof(T)];
        }

        private static MethodMap RegisterEndpointHandlers<T>()
        {
            MethodInfo[] methods = typeof(T).GetMethods(BindingFlags.NonPublic | BindingFlags.Instance);
            return methods
                .Aggregate(new MethodMap(), (handlers, m) =>
                {
                    Attribute attr = m.GetCustomAttribute(typeof(EndpointHandlerAttribute), false);
                    if (attr != null)
                    {
                        EndpointHandlerAttribute e = (EndpointHandlerAttribute) attr;
                        handlers.Add(e.Method, m);
                    }
                    return handlers;
                });
        }
    }
    
    
    
    public class MissingEndpointHandlerException : Exception
    {
        public MissingEndpointHandlerException(string method) : base($"Handler for [{method}] is either missing or incorrectly setup.")
        {
        }
    }
}