ShipmentService.cs

public class ShipmentService
{
    private readonly ShipmentDbContext _dbContext;

    public ShipmentService(ShipmentDbContext dbContext)
    {
        _dbContext = dbContext;
    }

    public void Arrive(Shipment shipment, int stopId)
    {
        var stop = shipment.GetStop(stopId);

        var previousStopsAreNotDeparted = shipment.GetAllStops().Any(x => x.StopId < stop.StopId && x.Status != StopStatus.Departed);
        if (previousStopsAreNotDeparted)
        {
            throw new InvalidOperationException("Previous stops have not departed.");
        }

        stop.SetStatus(StopStatus.Arrived);
        stop.SetArrivedDateTime(DateTime.UtcNow);
    }

    public void Pickup(Shipment shipment, int stopId)
    {
        var stop = shipment.GetStop(stopId);
        if (stop.Status != StopStatus.Arrived)
        {
            throw new InvalidOperationException("Stop is not yet arrived.");
        }

        stop.SetStatus(StopStatus.Departed);
        stop.SetDepartedDateTime(DateTime.UtcNow);
    }

    public void Deliver(Shipment shipment, int stopId)
    {
        var stop = shipment.GetStop(stopId);
        if (stop.Status != StopStatus.Arrived)
        {
            throw new InvalidOperationException("Stop is not yet arrived.");
        }

        stop.SetStatus(StopStatus.Departed);
        stop.SetDepartedDateTime(DateTime.UtcNow);
    }

    public bool IsComplete(Shipment shipment)
    {
        return shipment.GetAllStops().All(x => x.Status == StopStatus.Departed);
    }
}