Protect from menu taxon deletion

features/taxonomy/managing_taxons/deleting_taxon.feature

@@ -24,7 +24,7 @@ Feature: Deleting a taxon
         And the taxon named "Women" should no longer exist in the registry
         But the "Shovels" taxon should appear in the registry
 
-    @ui
+    @ui @javascript
     Scenario: Deleted taxon should disappear from the registry
         Given the store classifies its products as "T-Shirts" and "Caps"
         And the store operates on a channel named "Web Store"

src/Sylius/Behat/Context/Ui/Admin/ManagingTaxonsContext.php

@@ -393,7 +393,7 @@ final class ManagingTaxonsContext implements Context
     public function iShouldBeNotifiedThatICannotDeleteAMenuTaxonOfAnyChannel(): void
     {
         $this->notificationChecker->checkNotification(
-            'You cannot delete a menu taxon of any channel',
+            'You cannot delete a menu taxon of any channel.',
             NotificationType::failure()
         );
     }

src/Sylius/Bundle/CoreBundle/EventListener/TaxonDeletionListener.php

@@ -13,6 +13,7 @@ declare(strict_types=1);
 
 namespace Sylius\Bundle\CoreBundle\EventListener;
 
+use Sylius\Component\Channel\Repository\ChannelRepositoryInterface;
 use Sylius\Component\Core\Model\TaxonInterface;
 use Sylius\Component\Core\Promotion\Updater\Rule\TaxonAwareRuleUpdaterInterface;
 use Symfony\Component\EventDispatcher\GenericEvent;
@@ -25,17 +26,37 @@ final class TaxonDeletionListener
     /** @var SessionInterface */
     private $session;
 
+    /** @var ChannelRepositoryInterface $channelRepository */
+    private $channelRepository;
+
     /** @var TaxonAwareRuleUpdaterInterface[] */
     private $ruleUpdaters;
 
     public function __construct(
         SessionInterface $session,
+        ChannelRepositoryInterface $channelRepository,
         TaxonAwareRuleUpdaterInterface ...$ruleUpdaters
     ) {
         $this->session = $session;
+        $this->channelRepository = $channelRepository;
         $this->ruleUpdaters = $ruleUpdaters;
     }
 
+    public function protectFromRemovingMenuTaxon(GenericEvent $event): void
+    {
+        $taxon = $event->getSubject();
+        Assert::isInstanceOf($taxon, TaxonInterface::class);
+
+        $channel = $this->channelRepository->findOneBy(['menuTaxon' => $taxon]);
+        if ($channel !== null) {
+            /** @var FlashBagInterface $flashes */
+            $flashes = $this->session->getBag('flashes');
+            $flashes->add('error', 'sylius.taxon.menu_taxon_delete');
+
+            $event->stopPropagation();
+        }
+    }
+
     public function removeTaxonFromPromotionRules(GenericEvent $event): void
     {
         $taxon = $event->getSubject();

src/Sylius/Bundle/CoreBundle/Resources/config/services/listeners.xml

@@ -98,8 +98,10 @@
 
         <service id="sylius.listener.taxon_deletion" class="Sylius\Bundle\CoreBundle\EventListener\TaxonDeletionListener">
             <argument type="service" id="session" />
+            <argument type="service" id="sylius.repository.channel" />
             <argument type="service" id="sylius.promotion_rule_updater.total_of_items_from_taxon" />
             <argument type="service" id="sylius.promotion_rule_updater.has_taxon" />
+            <tag name="kernel.event_listener" event="sylius.taxon.pre_delete" method="protectFromRemovingMenuTaxon" />
             <tag name="kernel.event_listener" event="sylius.taxon.post_delete" method="removeTaxonFromPromotionRules" />
         </service>
     </services>

src/Sylius/Bundle/CoreBundle/spec/EventListener/TaxonDeletionListenerSpec.php

@@ -14,6 +14,8 @@ declare(strict_types=1);
 namespace spec\Sylius\Bundle\CoreBundle\EventListener;
 
 use PhpSpec\ObjectBehavior;
+use Sylius\Component\Channel\Repository\ChannelRepositoryInterface;
+use Sylius\Component\Core\Model\ChannelInterface;
 use Sylius\Component\Core\Model\TaxonInterface;
 use Sylius\Component\Core\Promotion\Updater\Rule\TaxonAwareRuleUpdaterInterface;
 use Symfony\Component\EventDispatcher\GenericEvent;
@@ -24,10 +26,60 @@ final class TaxonDeletionListenerSpec extends ObjectBehavior
 {
     function let(
         SessionInterface $session,
+        ChannelRepositoryInterface $channelRepository,
         TaxonAwareRuleUpdaterInterface $hasTaxonRuleUpdater,
         TaxonAwareRuleUpdaterInterface $totalOfItemsFromTaxonRuleUpdater
     ): void {
-        $this->beConstructedWith($session, $hasTaxonRuleUpdater, $totalOfItemsFromTaxonRuleUpdater);
+        $this->beConstructedWith(
+            $session,
+            $channelRepository,
+            $hasTaxonRuleUpdater,
+            $totalOfItemsFromTaxonRuleUpdater
+        );
+    }
+
+    function it_does_not_allow_to_remove_taxon_if_any_channel_has_it_as_a_menu_taxon(
+        SessionInterface $session,
+        ChannelRepositoryInterface $channelRepository,
+        GenericEvent $event,
+        TaxonInterface $taxon,
+        ChannelInterface $channel,
+        FlashBagInterface $flashes
+    ): void {
+        $event->getSubject()->willReturn($taxon);
+
+        $channelRepository->findOneBy(['menuTaxon' => $taxon])->willReturn($channel);
+
+        $session->getBag('flashes')->willReturn($flashes);
+        $flashes->add('error', 'sylius.taxon.menu_taxon_delete')->shouldBeCalled();
+        $event->stopPropagation()->shouldBeCalled();
+
+        $this->protectFromRemovingMenuTaxon($event);
+    }
+
+    function it_does_nothing_if_taxon_is_not_a_menu_taxon_of_any_channel(
+        SessionInterface $session,
+        ChannelRepositoryInterface $channelRepository,
+        GenericEvent $event,
+        TaxonInterface $taxon,
+        ChannelInterface $channel
+    ): void {
+        $event->getSubject()->willReturn($taxon);
+
+        $channelRepository->findOneBy(['menuTaxon' => $taxon])->willReturn(null);
+        $session->getBag('flashes')->shouldNotBeCalled();
+
+        $this->protectFromRemovingMenuTaxon($event);
+    }
+
+    function it_throws_an_exception_if_an_event_subject_is_not_taxon(GenericEvent $event): void
+    {
+        $event->getSubject()->willReturn('wrongSubject');
+
+        $this
+            ->shouldThrow(\InvalidArgumentException::class)
+            ->during('protectFromRemovingMenuTaxon', [$event])
+        ;
     }
 
     function it_adds_flash_that_promotions_have_been_updated(

src/Sylius/Bundle/UiBundle/Resources/translations/flashes.en.yml

@@ -26,3 +26,5 @@ sylius:
         update_error: 'There was an unexpected problem with updating a product variant. Please, try to update product variant again.'
     promotion:
         update_rules: 'Some rules of the promotions with codes %codes% have been updated.'
+    taxon:
+        menu_taxon_delete: 'You cannot delete a menu taxon of any channel.'