postoffice-1.0.x-dev/extensions/postoffice_file/src/EventSubscriber/FileAttachmentSubscriber.php

<?php

namespace Drupal\postoffice_file\EventSubscriber;

use Drupal\postoffice\Email\TemplateAttachmentsInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Mailer\Event\MessageEvent;
use Symfony\Component\Mime\Email;

/**
 * Attaches files supplied by the postoffice_file_X twig filters.
 *
 * Runs with priority -50 (after Symfony MessageListener which is responsible
 * for body rendering).
 */
class FileAttachmentSubscriber implements EventSubscriberInterface {

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents(): array {
    $events = [];
    $events[MessageEvent::class] = ['onMessage', -50];
    return $events;
  }

  /**
   * Attaches files supplied by the postoffice_file_X twig filters.
   */
  public function onMessage(MessageEvent $event): void {
    $message = $event->getMessage();
    if ($message instanceof Email && $message instanceof TemplateAttachmentsInterface) {
      $settings = $message->getTemplateAttachments()->getSettings();
      $attachments = $settings['postofficeFileAttachments'] ?? [];
      foreach ($attachments as $uri => $attachment) {
        ['name' => $name, 'mimeType' => $mimeType] = $attachment;
        $message->attachFromPath($uri, $name, $mimeType);
      }
    }
  }

}