Arrive.cs

public class ArriveHandler : IRequestHandler<Arrive>
{
    private readonly ShipmentDbContext _dbContext;
    private readonly IBus _bus;

    public ArriveHandler(ShipmentDbContext dbContext, IBus bus)
    {
        _dbContext = dbContext;
        _bus = bus;
    }

    public async Task<Unit> Handle(Arrive request, CancellationToken cancellationToken)
    {
        var allStops = await _dbContext.Stops.Where(x => x.ShipmentId == request.ShipmentId).ToArrayAsync();

        var stop = allStops.SingleOrDefault(x => x.StopId == request.StopId);
        if (stop == null)
        {
            throw new InvalidOperationException("Stop does not exist.");
        }

        if (stop.Status != StopStatus.InTransit)
        {
            throw new InvalidOperationException("Stop has already arrived.");
        }

        var previousStopsAreNotDeparted = allStops
            .Where(x => x.Scheduled < stop.Scheduled)
            .Any(x => x.Status != StopStatus.Departed);

        if (previousStopsAreNotDeparted)
        {
            throw new InvalidOperationException("Previous stops have not departed.");
        }

        stop.Status = StopStatus.Arrived;
        stop.Arrived = request.Arrived;

        await _dbContext.SaveChangesAsync();

        await _bus.Publish(new Arrived(stop.StopId, stop.Arrived));

        return Unit.Value;
    }
}