<?php

/**
 * Reset each talk's created and changed dates.
 */
function opdavies_talks_update_10101(): void {
  $entityTypeManager = \Drupal::entityTypeManager()->getStorage('node');

  $query = $entityTypeManager->getQuery();
  $query->condition('type', 'talk');

  $talkNodes = $entityTypeManager
    ->loadMultiple($query->accessCheck(FALSE)->execute());

  foreach ($talkNodes as $talk) {
    // Find the most recent event date for this talk.
    $lastEventDate = $talk->get('field_event_date')->getString();

    // Find the earliest event date for this talk.
    // All talks have events, so there will always be at least one event.
    $events = $talk->get('field_events')->referencedEntities();
    $firstEventDate = $events[0]->get('field_date')->getString();

    // Set the created date to the earliest event date (this will also set the `changed` date to now).
    $talk->set('created', strtotime($firstEventDate));
    $talk->save();

    // Override the `changed` date and set it to the most recent event date.
    $talk->set('changed', strtotime($lastEventDate));
    $talk->save();
  }
}