LunchLearnMefExample

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TripIt
{
    class Program
    {
        static void Main(string[] args)
        {
            var catalog = new AssemblyCatalog(System.Reflection.Assembly.GetExecutingAssembly());
            
            var container = new CompositionContainer(catalog);

            var tt = container.GetExport<BusinessLogicController>().Value;

            var tripRequest1 = new TripRequest { TripNumber = Guid.NewGuid(), TripName = "Trip #1" };
            var tripRequest2 = new TripRequest { TripNumber = Guid.NewGuid(), TripName = "Trip #2" };
            var tripRequest3 = new TripRequest { TripNumber = Guid.NewGuid(), TripName = "Trip #3" };

            var user1 = new User { ClientID = "A", Username = "User #1" };
            var user2 = new User { ClientID = "V", Username = "User #2" };
            var user3 = new User { ClientID = "E", Username = "User #3" };


            var controller = new BusinessLogicController(new TripRequestHandlerFactory(new ITripRequestHandler[] { new VectrusTripRequestHandler(), new ExellisTripRequestHandler(), new DefaultTripRequestHandler() }));

            User.CurrentUser = user1;
            controller.Submit(tripRequest1);

            User.CurrentUser = user2;
            controller.Submit(tripRequest2);

            User.CurrentUser = user3;
            controller.Submit(tripRequest3);
        }
    }

    public class User
    {
        public static User CurrentUser { get; set; }

        public string ClientID { get; set; }
        public string Username { get; set; }
    }

    public class TripRequest
    {
        public Guid TripNumber { get; set; }
        public string TripName { get; set; }
    }


    public interface ITripRequestHandler
    {
        bool IsAuthorized(User user);
        void Handle(TripRequest tripRequest);
    }

    public interface ITripRequestDefaultHandler : ITripRequestHandler
    {

    }

    [Export(typeof(ITripRequestHandler))]
    public class VectrusTripRequestHandler : ITripRequestHandler
    {
        void ITripRequestHandler.Handle(TripRequest tripRequest)
        {
            Console.WriteLine("vectrus business logic applied.");
        }

        bool ITripRequestHandler.IsAuthorized(User user)
        {
            return user.ClientID == "V";
        }
    }

    [Export(typeof(ITripRequestHandler))]
    public class ExellisTripRequestHandler : ITripRequestHandler
    {
        void ITripRequestHandler.Handle(TripRequest tripRequest)
        {
            Console.WriteLine("exellis business logic applied.");
        }

        bool ITripRequestHandler.IsAuthorized(User user)
        {
            return user.ClientID == "E";
        }
    }

    [Export(typeof(ITripRequestHandler))]
    [Export(typeof(ITripRequestDefaultHandler))]
    public class DefaultTripRequestHandler : ITripRequestHandler, ITripRequestDefaultHandler
    {
        void ITripRequestHandler.Handle(TripRequest tripRequest)
        {
            Console.WriteLine("default business logic applied.");
        }

        bool ITripRequestHandler.IsAuthorized(User user)
        {
            return true;
        }
    }

    public interface ITripRequestHandlerFactory
    {
        ITripRequestHandler Create();
    }

    [Export(typeof(ITripRequestHandlerFactory))]
    public class TripRequestHandlerFactory : ITripRequestHandlerFactory
    {
        private readonly IEnumerable<ITripRequestHandler> tripRequestHandlers;

        [ImportingConstructor]
        public TripRequestHandlerFactory([ImportMany]IEnumerable<ITripRequestHandler> tripRequestHandlers)
        {
            this.tripRequestHandlers = tripRequestHandlers;
        }

        ITripRequestHandler ITripRequestHandlerFactory.Create()
        {
            User user = User.CurrentUser;

            foreach (var tripRequestHandler in this.tripRequestHandlers)
            {
                if (!(tripRequestHandler is ITripRequestDefaultHandler))
                {
                    if (tripRequestHandler.IsAuthorized(user))
                        return tripRequestHandler;
                }
            }

            return
                this.tripRequestHandlers
                    .OfType<ITripRequestDefaultHandler>()
                    .FirstOrDefault();
        }
    }

    [Export]
    public class BusinessLogicController
    {
        private readonly ITripRequestHandlerFactory tripRequestHandlerFactory;

        [ImportingConstructor]
        public BusinessLogicController(ITripRequestHandlerFactory tripRequestHandlerFactory)
        {
            this.tripRequestHandlerFactory = tripRequestHandlerFactory;
        }

        public void Submit(TripRequest tripRequest)
        {
            var tripRequestHandler = this.tripRequestHandlerFactory.Create();
            tripRequestHandler.Handle(tripRequest);
        }
    }
}