❤️ Ian

AutofacStrategyPattern.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Autofac;
using Autofac.Features.Indexed;

namespace AutofacStrategyPattern
{
	class Program
	{
		static void Main(string[] args)
		{
			//Arrange
			var container = SetupContainer();

			var mpe = container.Resolve<MerchantPaymentExporter>();
			var ms = new MemoryStream();
			var sw = new StreamWriter(ms);
			
			//Act
			mpe.Export(ExportFormat.ACS, sw);
			mpe.Export(ExportFormat.Shelby, sw);

			//Ass
			sw.Flush();
			ms.Position = 0;
			ms.Seek(0, 0);
			var r = new StreamReader(ms);

			Console.WriteLine(r.ReadToEnd());
		}

		static IContainer SetupContainer()
		{
			var builder = new ContainerBuilder();
			RegisterMPW<AcsMerchantPaymentWriter>(builder, ExportFormat.ACS);
			RegisterMPW<ShelbyMerchantPaymentWriter>(builder, ExportFormat.Shelby);
			builder.RegisterType<MerchantPaymentExporter>();

			var container = builder.Build();
			return container;
		}

		static void RegisterMPW<T>(ContainerBuilder builder,ExportFormat format)
		{
			builder.RegisterType<T>()
			       .Keyed<IMerchantPaymentWriter>(format)
			       .AsImplementedInterfaces();
		}
	}

	public class MerchantPaymentExporter
	{
		readonly IIndex<ExportFormat, IMerchantPaymentWriter> _writers;

		public MerchantPaymentExporter(IIndex<ExportFormat,IMerchantPaymentWriter> writers)
		{
			_writers = writers;
		}

		public void Export(ExportFormat format, StreamWriter output)
		{
			var writer = default(IMerchantPaymentWriter);

			if (!_writers.TryGetValue(format, out writer)) {
				throw new Exception("No writer for: " + format);
			}

			writer.Write(Enumerable.Empty<object>(),output);
		}
	}

	public interface IMerchantPaymentWriter
	{
		void Write(IEnumerable<object> payments, StreamWriter writer);
	}

	public class AcsMerchantPaymentWriter : IMerchantPaymentWriter
	{
		public void Write(IEnumerable<object> payments, StreamWriter writer)
		{
			writer.Write("ACS");
		}
	}

	public class ShelbyMerchantPaymentWriter : IMerchantPaymentWriter
	{
		public void Write(IEnumerable<object> payments, StreamWriter writer)
		{
			writer.Write("Shelby");
		}
	}

	public enum ExportFormat
	{
		None,
		Arena, 
		ACS,
		Shelby
	}
}