OrderFulfillmentSubscriber.php

<?php
    namespace Drupal\afc_commerce\EventSubscriber;

    use Drupal\state_machine\Event\WorkflowTransitionEvent;
    use Drupal\Core\Language\LanguageManagerInterface;
    use Drupal\Core\Mail\MailManagerInterface;
    use Drupal\Core\StringTranslation\StringTranslationTrait;
    use Symfony\Component\EventDispatcher\EventSubscriberInterface;

    /**
     * Sends an email when the order transitions to Fulfillment.
     */
    class OrderFulfillmentSubscriber implements EventSubscriberInterface {

      use StringTranslationTrait;

      /**
       * The language manager.
       *
       * @var \Drupal\Core\Language\LanguageManagerInterface
       */
      protected $languageManager;

      /**
       * The mail manager.
       *
       * @var \Drupal\Core\Mail\MailManagerInterface
       */
      protected $mailManager;

      /**
       * Constructs a new OrderFulfillmentSubscriber object.
       *
       * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
       *   The language manager.
       * @param \Drupal\Core\Mail\MailManagerInterface $mail_manager
       *   The mail manager.
       */
      public function __construct(
        LanguageManagerInterface $language_manager,
        MailManagerInterface $mail_manager
      ) {
        $this->languageManager = $language_manager;
        $this->mailManager = $mail_manager;
      }

      /**
       * {@inheritdoc}
       */
      public static function getSubscribedEvents() {
        $events = [
          'commerce_order.place.post_transition' => ['sendEmail', -100],
        ];
        return $events;
      }

      /**
       * Sends the email.
       *
       * @param \Drupal\state_machine\Event\WorkflowTransitionEvent $event
       *   The transition event.
       */
      public function sendEmail(WorkflowTransitionEvent $event) {
        \Drupal::logger('afc_commerce')->notice('fired sendEmail post_trans');
        $order = $event->getEntity();
          $query = \Drupal::database()->select('commerce_order', 'c');
          $query->fields('p', ['field_customer_email_value']);
          $query->join('profile__field_customer_email', 'p', 'p.entity_id = c.billing_profile__target_id');
          $query->condition('c.order_id', $order->id());
          $result = $query->execute();
          while ($row = $result->fetchAssoc()) {
          	$email_to = $row['field_customer_email_value'];
          }
          //add case for empty, skip email
          
        $to = $email_to;
        $params = [
          'from' => $order->getStore()->getEmail(),
          'subject' => $this->t(
            'Regarding your order [#@number]',
            ['@number' => $order->getOrderNumber()]
          ),
          'body' => $this->t(
            'Your order with #@number that you have placed with us has been processed and is awaiting fulfillment.',
            ['@number' => $order->getOrderNumber()]
          ),
        ];

        // Set the language that will be used in translations.
        if ($customer = $order->getCustomer()) {
          $langcode = $customer->getPreferredLangcode();
        }
        else {
          $langcode = $this->languageManager->getDefaultLanguage()->getId();
        }

        //way to invoke the existing receipt template from themes/afc
        $this->mailManager->mail('commerce_order', 'receipt', $to, $langcode, $params);
        
      }

    }