class FieldStorageController

class FieldStorageController extends ConfigStorageController {

  /**
   * The module handler.
   *
   * @var \Drupal\Core\Extension\ModuleHandler
   */
  protected $moduleHandler;

  /**
   * The entity manager.
   *
   * @var \Drupal\Core\Entity\EntityManager
   */
  protected $entityManager;

  /**
   * The state keyvalue collection.
   *
   * @var \Drupal\Core\KeyValueStore\KeyValueStoreInterface
   */
  protected $state;

  /**
   * Constructs a FieldStorageController object.
   *
   * @param string $entity_type
   *   The entity type for which the instance is created.
   * @param array $entity_info
   *   An array of entity info for the entity type.
   * @param \Drupal\Core\Config\ConfigFactory $config_factory
   *   The config factory service.
   * @param \Drupal\Core\Config\StorageInterface $config_storage
   *   The config storage service.
   * @param \Drupal\Core\Entity\EntityManager $entity_manager
   *   The entity manager.
   * @param \Drupal\Core\Extension\ModuleHandler $module_handler
   *   The module handler.
   * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $state
   *   The state key value store.
   */
  public function __construct($entity_type, array $entity_info, ConfigFactory $config_factory, StorageInterface $config_storage, EntityManager $entity_manager, ModuleHandler $module_handler, KeyValueStoreInterface $state) {
    parent::__construct($entity_type, $entity_info, $config_factory, $config_storage);
    $this->entityManager = $entity_manager;
    $this->moduleHandler = $module_handler;
    $this->state = $state;
  }

  /**
   * {@inheritdoc}
   */
  public static function createInstance(ContainerInterface $container, $entity_type, array $entity_info) {
    return new static($entity_type, $entity_info, $container
      ->get('config.factory'), $container
      ->get('config.storage'), $container
      ->get('plugin.manager.entity'), $container
      ->get('module_handler'), $container
      ->get('state'));
  }

  /**
   * {@inheritdoc}
   */
  public function loadByProperties(array $conditions = array()) {

    // Include instances of inactive fields if specified in the
    // $conditions parameters.
    $include_inactive = $conditions['include_inactive'];
    unset($conditions['include_inactive']);

    // Include deleted instances if specified in the $conditions parameters.
    $include_deleted = $conditions['include_deleted'];
    unset($conditions['include_deleted']);

    // Get fields stored in configuration.
    if (isset($conditions['field_name'])) {

      // Optimize for the most frequent case where we do have a specific ID.
      $fields = $this->entityManager
        ->getStorageController($this->entityType)
        ->load(array(
        $conditions['field_name'],
      ));
    }
    else {

      // No specific ID, we need to examine all existing fields.
      $fields = $this->entityManager
        ->getStorageController($this->entityType)
        ->load();
    }

    // Merge deleted fields (stored in state) if needed.
    if ($include_deleted) {
      $deleted_fields = $this->state
        ->get('field.field.deleted') ?: array();
      foreach ($deleted_fields as $id => $config) {
        $fields[$id] = $this->entityManager
          ->getStorageController($this->entityType)
          ->create($config);
      }
    }

    // Translate "do not include inactive instances" into actual conditions.
    if (!$include_inactive) {
      $conditions['active'] = TRUE;
      $conditions['storage.active'] = TRUE;
    }

    // Collect matching fields.
    $matching_fields = array();
    foreach ($fields as $field) {
      foreach ($conditions as $key => $value) {

        // Extract the actual value against which the condition is checked.
        switch ($key) {
          case 'storage.active':
            $checked_value = $field->storage['active'];
            break;
          case 'field_name':
            $checked_value = $field->id;
            break;
          default:
            $checked_value = $field->{$key};
            break;
        }

        // Skip to the next field as soon as one condition does not match.
        if ($checked_value != $value) {
          continue 2;
        }
      }
      $this->moduleHandler
        ->invokeAll('field_read_field', $field);

      // When returning deleted fields, key the results by UUID since they can
      // include several fields with the same ID.
      $key = $include_deleted ? $field->uuid : $field->id;
      $matching_fields[$key] = $field;
    }
    return $matching_fields;
  }

}