A Drupal Commerce event subscriber for automatic order fulfillment

OrderFulfillmentSubscriber.php

<?php

namespace Drupal\commerce_icu_post_checkout\EventSubscriber;

use Drupal\commerce_icu_post_checkout\AutoFulfillmentManagerInterface;
use Drupal\commerce_order\Entity\OrderInterface;
use Drupal\state_machine\Event\WorkflowTransitionEvent;
use Psr\Log\LoggerInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 *  Determine whether to split an order and do so if appropriate when an order is placed.
 */
class OrderFulfillmentSubscriber implements EventSubscriberInterface {

  /**
   * The auto fulfillment manager.
   *
   * @var \Drupal\commerce_icu_post_checkout\AutoFulfillmentManagerInterface
   */
  protected $autoFulfillmentManager;

  /**
   * Constructs a new OrderFulfillmentSubscriber object.
   *
   * @param \Drupal\commerce_icu_post_checkout\AutoFulfillmentManagerInterface $auto_fulfillment_manager
   *   The auto fulfillment manager.
   */
  public function __construct(
      AutoFulfillmentManagerInterface $auto_fulfillment_manager
    ) {
    $this->autoFulfillmentManager = $auto_fulfillment_manager;
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    // We subscribe at a lower priority than
    // OrderNumberSubscriber::setOrderNumber to ensure the order number has
    // been set before attempting to autofulfill.
    $events = [
      'commerce_order.pre_transition' => ['checkOrderAtFulfillment', -50],
    ];
    return $events;
  }

  /**
   * Checks whether an order has just transitioned to fullfillment. If so,
   * attempt to autofulfill, and if successful transition to complete
   *
   * @param \Drupal\state_machine\Event\WorkflowTransitionEvent $event
   *   The event we subscribed to.
   */
  public function checkOrderAtFulfillment(WorkflowTransitionEvent $event) {
    $toState = $event->getToState();

    if ($toState->getId() != 'fulfillment') {
      return;
    }

    /** @var \Drupal\commerce_order\Entity\OrderInterface $order */
    $order = $event->getEntity();

    $order_fulfilled = $this->autoFulfillmentManager->fulfill($order);

    // If the order was completely fulfilled, progress to complete.
    // We manually trigger postSave before and preSave after applying the
    // transition to allow post transition events to be fired for the
    // transition triggering fulfillment and allow pre transition events to
    // be fired for the transition to complete
    if ($order_fulfilled) {
      $order->getState()->postSave(true);
      $order->getState()->applyTransitionById('fulfill');
      $order->getState()->preSave();
    }
  }

}