Automatically update the created date for talks

Automatically update the created dates for talk nodes so that they match
the most-future event. This means that the talks are ordered correctly
on the Talks page.

web/modules/custom/custom/src/EventSubscriber/UpdateTalkCreatedDateOnSave.php

@@ -0,0 +1,64 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\custom\EventSubscriber;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\hook_event_dispatcher\Event\Entity\BaseEntityEvent;
+use Drupal\hook_event_dispatcher\HookEventDispatcherInterface;
+use Drupal\paragraphs\ParagraphInterface;
+use Illuminate\Support\Collection;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Set the created date for a talk to be the last date that the talk is given.
+ */
+final class UpdateTalkCreatedDateOnSave implements EventSubscriberInterface {
+
+  public static function getSubscribedEvents() {
+    return [
+      HookEventDispatcherInterface::ENTITY_INSERT => 'entityInsertOrUpdate',
+      HookEventDispatcherInterface::ENTITY_UPDATE => 'entityInsertOrUpdate',
+    ];
+  }
+
+  public function entityInsertOrUpdate(BaseEntityEvent $event): void {
+    if ($event->getEntity()->getEntityTypeId() != 'node') {
+      return;
+    }
+
+    if ($event->getEntity()->bundle() != 'talk') {
+      return;
+    }
+
+    $this->updateCreatedDate($event->getEntity());
+  }
+
+  private function updateCreatedDate(EntityInterface $talk): void {
+    if (!$eventDate = $this->findLatestEventDate($talk)) {
+      return;
+    }
+
+    $talkDate = (new \DateTime($eventDate))->getTimestamp();
+
+    if ($talkDate == $talk->get('created')->getString()) {
+      return;
+    }
+
+    $talk->set('created', $talkDate);
+  }
+
+  /**
+   * Find the date for the latest event.
+   *
+   * @return string|null
+   */
+  private function findLatestEventDate(EntityInterface $talk) {
+    return Collection::make($talk->get('field_events')->referencedEntities())
+      ->map(fn(ParagraphInterface $event) => $event->get('field_date')
+        ->getString())
+      ->max();
+  }
+
+}