aggregate.cs

class Order : Aggregate
{
    static Order()
    {
        Given<Order, OrderStarted>((x, e) =>
        {
            x.Id = e.Id;
            x.customerId = e.CustomerId;
            x.status = OrderStatus.Open;
            x.tickets = new List<Ticket>();
        });

        Given<Order, TicketsReserved>((x, e) =>
        {
            var ticket = new Ticket(e.TicketId, e.Quantity);

            x.status = OrderStatus.Reserved;
            x.tickets.Add(ticket);
            x.outstandingBalance += e.TicketPrice * e.Quantity;
        });

        Given<Order, PaymentReceived>((x, e) =>
        {
            x.outstandingBalance -= e.Amount;
            x.status = OrderStatus.Closed;
        });
    }

    private Guid customerId;
    private OrderStatus status;
    private List<Ticket> tickets;
    private decimal outstandingBalance;

    public Order(Guid id, Guid customerId)
    {
        Then(new OrderStarted(id, customerId));
    }

    public void When(ReserveTickets command)
    {
        Then(new TicketsReserved(command.TicketId, command.Quantity, 25));
    }

    public void When(MakePayment command)
    {
        Then(new PaymentReceived(123));
    }
}

struct Ticket
{
    public Ticket(Guid ticketId, int quantity)
    {
        TicketId = ticketId;
        Quantity = quantity;
    }

    public Guid TicketId { get; }
    public int Quantity { get; }
}

enum OrderStatus
{
    Open,
    Reserved,
    Closed
}


abstract class Aggregate
{
    public Guid Id { get; protected set; }

    protected static void Given<TAggregate, TEvent>(Action<TAggregate, TEvent> action)
    {

    }

    protected void Then<TEvent>(TEvent e)
    {

    }
}


class ReserveTickets
{
    public ReserveTickets(Guid ticketId, int quantity)
    {
        TicketId = ticketId;
        Quantity = quantity;
    }

    public Guid TicketId { get; }
    public int Quantity { get; }
}

class MakePayment
{
    public MakePayment(string paymentToken)
    {
        PaymentToken = paymentToken;
    }

    public string PaymentToken { get; }
}

class OrderStarted
{
    public OrderStarted(Guid id, Guid customerId)
    {
        Id = id;
        CustomerId = customerId;
    }

    public Guid Id { get; }
    public Guid CustomerId { get; }
}

class TicketsReserved
{
    public TicketsReserved(Guid ticketId, int quantity, decimal ticketPrice)
    {
        TicketId = ticketId;
        Quantity = quantity;
        TicketPrice = ticketPrice;
    }

    public Guid TicketId { get; }
    public int Quantity { get; }
    public decimal TicketPrice { get; }
}

class PaymentReceived
{
    public PaymentReceived(decimal amount)
    {
        Amount = amount;
    }

    public decimal Amount { get; }
}