Author: Richard Seroter

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Runtime.Serialization;

namespace Seroter.AspNetWebApi.VersionedSvc.Models
{
    [DataContract(Name = "Account", Namespace = "")]
    public class Account
    {
        [DataMember]
        public int Id { get; set; }
        [DataMember]
        public string Name { get; set; }
        [DataMember]
        public string TimeZone { get; set; }
        [DataMember]
        public string OwnerName { get; set; }
    }
}

public class AccountsController : ApiController
    {
        /// <summary>
        /// instantiate list of accounts
        /// </summary>
        Account[] accounts = new Account[]
        {
            new Account { Id = 100, Name = "Big Time Consulting", OwnerName = "Harry Simpson", TimeZone = "PST"},
            new Account { Id = 101, Name = "BTS Partners", OwnerName = "Bobby Thompson", TimeZone = "MST"},
            new Account { Id = 102, Name = "Westside Industries", OwnerName = "Ken Finley", TimeZone = "EST"},
            new Account { Id = 103, Name = "Cricket Toys", OwnerName = "Tim Headley", TimeZone = "PST"}
        };

        /// <summary>
        /// Returns all the accounts; happens automatically based on operation name
        /// </summary>
        /// <returns></returns>
        public IEnumerable<Account> GetAllAccounts()
        {
            return accounts;
        }

        /// <summary>
        /// Returns a single account and uses an explicit [HttpGet] attribute
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        [HttpGet]
        public Account GetAccount(int id)
        {
            Account result = accounts.FirstOrDefault(acct => acct.Id == id);

            if (result == null)
            {
                HttpResponseMessage err = new HttpResponseMessage(HttpStatusCode.NotFound)
                {
                    ReasonPhrase = "No product found with that ID"
                };

                throw new HttpResponseException(err);
            }

            return result;
        }

        /// <summary>
        /// Creates a new account and returns HTTP code and URI of new resource representation
        /// </summary>
        /// <param name="a"></param>
        /// <returns></returns>
        public HttpResponseMessage PostAccount(Account a)
        {
            Random r = new Random(1);

            a.Id = r.Next();
            var resp = Request.CreateResponse<Account>(HttpStatusCode.Created, a);

            //get URI of new resource and send it back in the header
            string uri = Url.Link("DefaultApi", new { id = a.Id });
            resp.Headers.Location = new Uri(uri);

            return resp;
        }
    }

 /// <summary>
    /// Selects which controller to serve up based on HTTP header value
    /// </summary>
    public class HeaderVersionControllerSelector : IHttpControllerSelector
    {
        //store config that gets passed on on startup
        private HttpConfiguration _config;
        //dictionary to hold the list of possible controllers
        private Dictionary<string, HttpControllerDescriptor> _controllers = new Dictionary<string, HttpControllerDescriptor>(StringComparer.OrdinalIgnoreCase);

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="config"></param>
        public HeaderVersionControllerSelector(HttpConfiguration config)
        {
            //set member variable
            _config = config;

            //manually inflate controller dictionary
            HttpControllerDescriptor d1 = new HttpControllerDescriptor(_config, "AccountsControllerV1", typeof(AccountsControllerV1));
            HttpControllerDescriptor d2 = new HttpControllerDescriptor(_config, "AccountsControllerV2", typeof(AccountsControllerV2));
            HttpControllerDescriptor d3 = new HttpControllerDescriptor(_config, "InvoicesControllerV1", typeof(InvoicesControllerV1));
            _controllers.Add("AccountsControllerV1", d1);
            _controllers.Add("AccountsControllerV2", d2);
            _controllers.Add("InvoicesControllerV1", d3);
        }

        /// <summary>
        /// Implement required operation and return list of controllers
        /// </summary>
        /// <returns></returns>
        public IDictionary<string, HttpControllerDescriptor> GetControllerMapping()
        {
            return _controllers;
        }

        /// <summary>
        /// Implement required operation that returns controller based on version, URL path
        /// </summary>
        /// <param name="request"></param>
        /// <returns></returns>
        public HttpControllerDescriptor SelectController(System.Net.Http.HttpRequestMessage request)
        {
            //yank out version value from HTTP header
            IEnumerable<string> values;
            int? apiVersion = null;
            if (request.Headers.TryGetValues("X-Api-Version", out values))
            {
                foreach (string value in values)
                {
                    int version;
                    if (Int32.TryParse(value, out version))
                    {
                        apiVersion = version;
                        break;
                    }
                }
            }

            //get the name of the route used to identify the controller
            string controllerRouteName = this.GetControllerNameFromRequest(request);

            //build up controller name from route and version #
            string controllerName = controllerRouteName + "ControllerV" + apiVersion;

            //yank controller type out of dictionary
            HttpControllerDescriptor controllerDescriptor;
            if (this._controllers.TryGetValue(controllerName, out controllerDescriptor))
            {
                return controllerDescriptor;
            }
            else
            {
                return null;
            }
        }

        /// <summary>
        /// Helper method that pulls the name of the controller from the route
        /// </summary>
        /// <param name="request"></param>
        /// <returns></returns>
        private string GetControllerNameFromRequest(HttpRequestMessage request)
        {
            IHttpRouteData routeData = request.GetRouteData();

            // Look up controller in route data
            object controllerName;
            routeData.Values.TryGetValue("controller", out controllerName);

            return controllerName.ToString();
        }
    }

public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();

            WebApiConfig.Register(GlobalConfiguration.Configuration);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);

            //added to support runtime controller selection
            GlobalConfiguration.Configuration.Services.Replace(typeof(IHttpControllerSelector),
                                                           new HeaderVersionControllerSelector(GlobalConfiguration.Configuration));
        }
    }