// Original Code
public function makeBooking($cargo, $voyage)
{
    // This is an over-simplification of the logic for determining if a ship is over-booked
    $maxBooking = $voyage->getCapacity() * 1.1;
    if ($voyage->getBookedCargoSize() + $cargo->getSize() > $maxBooking) {
        return false;
    }
    return $voyage->addCargo($cargo);
}

// Alternative 1: Create a private method, or a method on the entity.
public function makeBooking($cargo, $voyage)
{
    $maxBooking = $this->getMaxBookingSize($voyage);
    if ($voyage->getBookedCargoSize() + $cargo->getSize() > $maxBooking) {
        return false;
    }
    return $voyage->addCargo($cargo);
}

private function getMaxBookingSize($voyage)
{
    // This is a simplification of the logic for determining if a ship is over-booked
    if ($voyage->isDomestic()) {
        return $voyage->getCapacity() * 1.2;
    }
    return $voyage->getCapactiy() * 1.1;
}

// Alternative 2: Use a Policy class to keep the business logic explicit and easy to find / update
class BookingPolicy
{
    public function isAllowed($cargo, $voyage)
    {
         // This is a simplification of the logic for determining if a ship is over-booked
        if ($voyage->isDomestic()) {
            $maxBooking = $voyage->getCapacity() * 1.2;
        } else {
            $maxBooking = $voyage->getCapactiy() * 1.1;
        }
        return $voyage->getBookedCargoSize() + $cargo->getSize() > $maxBooking);
    }
}

public function makeBooking($cargo, $voyage)
{
    if ($bookingPolicy->isAllowed($cargo, $voyage) {
        $voyage->addCargo($cargo);
    } else {
        return null;
    }
}