Event sourced handler

Commands.cs

public class RequestReservation { }
public class ConfirmReservation { }

Events.cs

public class ReservationRequested { }
public class ReservationConfirmed { }

Handler.cs

public abstract class Handler<TState>
{
    protected void Stream(Func<TState, string> action)
    {
            
    }

    protected void Given<TEvent>(Func<TState, TEvent, TState> given)
    {
            
    }

    protected void When<TMessage>(Func<TState, TMessage, IEnumerable<object>> when)
    {
            
    }
}

ReservationHandler.cs

public class ReservationHandler : Handler<ReservationState>
{
    public ReservationHandler()
    {
        // How dafuq does this work?
        Stream(s => $"Reservation-{s.Id}");

        Given<ReservationRequested>((s, e) =>
        {
            // Mutate state
            return s;
        });

        Given<ReservationConfirmed>((s, e) =>
        {
            // Mutate state
            return s;
        });

        When<RequestReservation>((s, e) =>
        {
            // Some business logic stuff
            return new[]
            {
                new ReservationRequested()
            };
        });

        When<ConfirmReservation>((s, e) =>
        {
            // Some business logic stuff
            return new[]
            {
                new ReservationConfirmed()
            };
        });
    }
}

ReservationState.cs

public class ReservationState
{
    public Guid Id { get; }
    public string TicketId { get; }
    public int Quantity { get; }

    public ReservationState(Guid id, string ticketId, int quantity)
    {
        Id = id;
        TicketId = ticketId;
        Quantity = quantity;
    }
}