CustomerRevenueSaga.cs

public class CustomerRevenueSaga : Saga<CustomerRevenue>
{
    public CustomerRevenueSaga(ICustomerRevenueStore store)
    {
        When<OrderPlaced>(
            accessMemory: async msg => new Memory(await store.GetByCustomerId(msg.CustomerId), store.Save),
            transform: (msg, state) =>
            {
                var nextState = state?.Clone() ?? new CustomerRevenue { CustomerId = msg.CustomerId };
                nextState.PendingOrderAmounts[msg.Id] = msg.Amount;
                return Task.FromResult<ITransformResult>(new TransformResult(nextState));
            });

        When<OrderCancelled>(
            accessMemory: async msg => new Memory(await store.GetByOrderId(msg.OrderId), store.Save),
            transform: (msg, state) =>
            {
                var nextState = state?.Clone();
                nextState?.PendingOrderAmounts.Remove(msg.OrderId);
                return Task.FromResult<ITransformResult>(new TransformResult(nextState));
            });

        When<OrderDelivered>(
            accessMemory: async msg => new Memory(await store.GetByOrderId(msg.OrderId), store.Save),
            transform: (msg, state) =>
            {
                var nextState = state?.Clone();
                var orderAmount = nextState?.PendingOrderAmounts[msg.OrderId];
                if (orderAmount.HasValue)
                {
                    nextState.AggregatedRevenue += orderAmount.Value;
                    nextState.PendingOrderAmounts.Remove(msg.OrderId);
                }
                return Task.FromResult<ITransformResult>(new TransformResult(nextState));
            });
    }
}

To create an instance + connect it to a bus (automatically wiring up topic subscriptions):

var saga = new CustomerRevenueSaga(myStore);
await saga.Connect(myBus);

The base Saga definition, for reference: https://gist.github.com/Hihaj/8c9d002a0e1eb545261b