[Sylius] Zone based promotion rule

services.yml

app.promotion_rule_checker.shipping_zone:
    class: AppBundle\Checker\Rule\ShippingZoneRuleChecker
    arguments:
        - "@sylius.repository.zone"
    tags:
        - { name: sylius.promotion_rule_checker, type: shipping_zone,
            label: Shipping zone, form_type: AppBundle\Form\Admin\Promotion\ShippingZoneConfigurationType }

ShippingZoneConfigurationType.php

<?php

namespace AppBundle\Form\Admin\Promotion;

use Sylius\Bundle\AddressingBundle\Form\Type\ZoneCodeChoiceType;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;

final class ShippingZoneConfigurationType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('zone', ZoneCodeChoiceType::class)
        ;
    }

    public function getBlockPrefix()
    {
        return 'app_bundle_shipping_zone_configuration_type';
    }
}

ShippingZoneRuleChecker.php

<?php

declare(strict_types=1);

namespace AppBundle\Checker\Rule;

use Sylius\Component\Promotion\Checker\Rule\RuleCheckerInterface;
use Sylius\Component\Promotion\Model\PromotionSubjectInterface;
use Sylius\Component\Core\Model\OrderInterface;
use Sylius\Component\Promotion\Exception\UnsupportedTypeException;

final class ShippingZoneRuleChecker implements RuleCheckerInterface
{
    /** @var \Doctrine\ORM\EntityRepository */
    private $zoneRepository;

    public const TYPE = 'shipping_zone';

    /**
     * ShippingZoneRuleChecker constructor.
     * @param \Doctrine\ORM\EntityRepository $zoneRepository
     */
    public function __construct(\Doctrine\ORM\EntityRepository $zoneRepository)
    {
        $this->zoneRepository = $zoneRepository;
    }


    public function isEligible(PromotionSubjectInterface $subject, array $configuration): bool
    {
        if (!$subject instanceof OrderInterface) {
            throw new UnsupportedTypeException($subject, OrderInterface::class);
        }
        if (null === $shipment = $subject->getShipments()[0]) {
            return false;
        }
        $method = $shipment->getMethod();
        if (null === $method) {
            return false;
        }
        if (null === $zone = $method->getZone()) {
            return false;
        }
        return $configuration['zone'] === $zone->getCode();
    }
}