ES Demo snippet

gistfile1.txt

using System;
using System.Collections.Generic;

namespace EventSourcing
{
  public class Program
	{
		public static void Main(string[] args)
		{
			var acc = new Account();

			acc.Withdraw(10);
			acc.Withdraw(20);
			acc.Withdraw(30);
			acc.Withdraw(40);
			acc.Deposit(50);

			foreach (var @event in acc.RecordedEvents())
				Console.WriteLine(@event);

			var acc2 = new Account();
			acc2.Initialize(acc.RecordedEvents());
			acc2.Deposit(10);
			acc2.Deposit(20);
			acc2.Deposit(30);
			acc2.Deposit(40);
			acc2.Deposit(50);
			acc2.Withdraw(500000);

			foreach (var @event in acc2.RecordedEvents())
				Console.WriteLine(@event);

			Console.ReadLine();
		}

		public class Account
		{
			private int _amount = 0;

			private readonly EventRecorder _eventRecorder;

			public Account()
			{
				_eventRecorder = new EventRecorder();
			}

			public void Initialize(IEnumerable<IEvent> events)
			{
				foreach (var @event in events)
					When((dynamic)@event);
			}

			public IEnumerable<IEvent> RecordedEvents()
			{
				return _eventRecorder.RecordedEvents();
			}

			public void Deposit(int amount)
			{
				Apply(new AmountDeposited(amount));
			}

			public void Withdraw(int amount)
			{
				if (amount > AmountPolicy.Maximum)
				{
					_eventRecorder.Record(new WithdrawalAmountExceeded(amount));

					return;
				}

				Apply(new AmountWithdrawn(amount));
			}

			private void Apply(IEvent @event)
			{
				When((dynamic)@event);
				_eventRecorder.Record(@event);
			}

			private void When(AmountWithdrawn @event)
			{
				_amount -= @event.Amount;
			}

			private void When(AmountDeposited @event)
			{
				_amount += @event.Amount;
			}
		}

		public interface IEvent { }

		public class EventRecorder
		{
			private readonly List<IEvent> _events = new List<IEvent>();

			public void Record(IEvent @event)
			{
				_events.Add(@event);
			}

			public IEnumerable<IEvent> RecordedEvents()
			{
				return _events;
			}
		}

		public class AmountWithdrawn : IEvent
		{
			public AmountWithdrawn(int amount)
			{
				Amount = amount;
			}

			public int Amount { get; private set; }

			public override string ToString()
			{
				return string.Format("Amount withdrawn: {0}", Amount);
			}
		}

		public class AmountDeposited : IEvent
		{
			public AmountDeposited(int amount)
			{
				Amount = amount;
			}

			public int Amount { get; private set; }

			public override string ToString()
			{
				return string.Format("Amount deposited: {0}", Amount);
			}
		}

		public class WithdrawalAmountExceeded : IEvent
		{
			public WithdrawalAmountExceeded(int amount)
			{
				Amount = amount;
			}

			public int Amount { get; private set; }

			public override string ToString()
			{
				return string.Format("Amount exceeded: {0}", Amount);
			}
		}

		public class AmountPolicy
		{
			public static int Maximum { get { return 5000; } }
		}
	}
}