class ConfigEntityStorage

class ConfigEntityStorage extends EntityStorageBase implements ConfigEntityStorageInterface, ImportableEntityStorageInterface {
    
    /**
     * Length limit of the configuration entity ID.
     *
     * Most file systems limit a file name's length to 255 characters, so
     * ConfigBase::MAX_NAME_LENGTH restricts the full configuration object name
     * to 250 characters (leaving 5 for the file extension). The config prefix
     * is limited by ConfigEntityType::PREFIX_LENGTH to 83 characters, so this
     * leaves 166 remaining characters for the configuration entity ID, with 1
     * additional character needed for the joining dot.
     *
     * @see \Drupal\Core\Config\ConfigBase::MAX_NAME_LENGTH
     * @see \Drupal\Core\Config\Entity\ConfigEntityType::PREFIX_LENGTH
     */
    const MAX_ID_LENGTH = 166;
    
    /**
     * {@inheritdoc}
     */
    protected $uuidKey = 'uuid';
    
    /**
     * The config factory service.
     *
     * @var \Drupal\Core\Config\ConfigFactoryInterface
     */
    protected $configFactory;
    
    /**
     * The config storage service.
     *
     * @var \Drupal\Core\Config\StorageInterface
     */
    protected $configStorage;
    
    /**
     * The language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Static cache of entities, keyed first by entity ID, then by an extra key.
     *
     * The additional cache key is to maintain separate caches for different
     * states of config overrides.
     *
     * @var array
     * @see \Drupal\Core\Config\ConfigFactoryInterface::getCacheKeys().
     */
    protected $entities = [];
    
    /**
     * Determines if the underlying configuration is retrieved override free.
     *
     * @var bool
     */
    protected $overrideFree = FALSE;
    
    /**
     * Constructs a ConfigEntityStorage object.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type definition.
     * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
     *   The config factory service.
     * @param \Drupal\Component\Uuid\UuidInterface $uuid_service
     *   The UUID service.
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     * @param \Drupal\Core\Cache\MemoryCache\MemoryCacheInterface|null $memory_cache
     *   The memory cache backend.
     */
    public function __construct(EntityTypeInterface $entity_type, ConfigFactoryInterface $config_factory, UuidInterface $uuid_service, LanguageManagerInterface $language_manager, MemoryCacheInterface $memory_cache = NULL) {
        parent::__construct($entity_type, $memory_cache);
        $this->configFactory = $config_factory;
        $this->uuidService = $uuid_service;
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
        return new static($entity_type, $container->get('config.factory'), $container->get('uuid'), $container->get('language_manager'), $container->get('entity.memory_cache'));
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadRevision($revision_id) {
        return NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteRevision($revision_id) {
        return NULL;
    }
    
    /**
     * Returns the prefix used to create the configuration name.
     *
     * The prefix consists of the config prefix from the entity type plus a dot
     * for separating from the ID.
     *
     * @return string
     *   The full configuration prefix, for example 'views.view.'.
     */
    protected function getPrefix() {
        return $this->entityType
            ->getConfigPrefix() . '.';
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getIDFromConfigName($config_name, $config_prefix) {
        return substr($config_name, strlen($config_prefix . '.'));
    }
    
    /**
     * {@inheritdoc}
     */
    protected function doLoadMultiple(array $ids = NULL) {
        $prefix = $this->getPrefix();
        // Get the names of the configuration entities we are going to load.
        if ($ids === NULL) {
            $names = $this->configFactory
                ->listAll($prefix);
        }
        else {
            $names = [];
            foreach ($ids as $id) {
                // Add the prefix to the ID to serve as the configuration object name.
                $names[] = $prefix . $id;
            }
        }
        // Load all of the configuration entities.
        
        /** @var \Drupal\Core\Config\Config[] $configs */
        $configs = [];
        $records = [];
        foreach ($this->configFactory
            ->loadMultiple($names) as $config) {
            $id = $config->get($this->idKey);
            $records[$id] = $this->overrideFree ? $config->getOriginal(NULL, FALSE) : $config->get();
            $configs[$id] = $config;
        }
        $entities = $this->mapFromStorageRecords($records, $configs);
        // Config entities wrap config objects, and therefore they need to inherit
        // the cacheability metadata of config objects (to ensure e.g. additional
        // cacheability metadata added by config overrides is not lost).
        foreach ($entities as $id => $entity) {
            // But rather than simply inheriting all cacheability metadata of config
            // objects, we need to make sure the self-referring cache tag that is
            // present on Config objects is not added to the Config entity. It must be
            // removed for 3 reasons:
            // 1. When renaming/duplicating a Config entity, the cache tag of the
            //    original config object would remain present, which would be wrong.
            // 2. Some Config entities choose to not use the cache tag that the under-
            //    lying Config object provides by default (For performance and
            //    cacheability reasons it may not make sense to have a unique cache
            //    tag for every Config entity. The DateFormat Config entity specifies
            //    the 'rendered' cache tag for example, because A) date formats are
            //    changed extremely rarely, so invalidating all render cache items is
            //    fine, B) it means fewer cache tags per page.).
            // 3. Fewer cache tags is better for performance.
            $self_referring_cache_tag = [
                'config:' . $configs[$id]->getName(),
            ];
            $config_cacheability = CacheableMetadata::createFromObject($configs[$id]);
            $config_cacheability->setCacheTags(array_diff($config_cacheability->getCacheTags(), $self_referring_cache_tag));
            $entity->addCacheableDependency($config_cacheability);
        }
        return $entities;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function doCreate(array $values) {
        // Set default language to current language if not provided.
        $values += [
            $this->langcodeKey => $this->languageManager
                ->getCurrentLanguage()
                ->getId(),
        ];
        $entity = new $this->entityClass($values, $this->entityTypeId);
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function doDelete($entities) {
        foreach ($entities as $entity) {
            $this->configFactory
                ->getEditable($this->getPrefix() . $entity->id())
                ->delete();
        }
    }
    
    /**
     * Implements Drupal\Core\Entity\EntityStorageInterface::save().
     *
     * @throws \Drupal\Core\Entity\EntityMalformedException
     *   When attempting to save a configuration entity that has no ID.
     */
    public function save(EntityInterface $entity) {
        // Configuration entity IDs are strings, and '0' is a valid ID.
        $id = $entity->id();
        if ($id === NULL || $id === '') {
            throw new EntityMalformedException('The entity does not have an ID.');
        }
        // Check the configuration entity ID length.
        // @see \Drupal\Core\Config\Entity\ConfigEntityStorage::MAX_ID_LENGTH
        // @todo Consider moving this to a protected method on the parent class, and
        //   abstracting it for all entity types.
        if (strlen($entity->get($this->idKey)) > static::MAX_ID_LENGTH) {
            throw new ConfigEntityIdLengthException("Configuration entity ID {$entity->get($this->idKey)} exceeds maximum allowed length of " . static::MAX_ID_LENGTH . " characters.");
        }
        return parent::save($entity);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function doSave($id, EntityInterface $entity) {
        $is_new = $entity->isNew();
        $prefix = $this->getPrefix();
        $config_name = $prefix . $entity->id();
        if ($id !== $entity->id()) {
            // Renaming a config object needs to cater for:
            // - Storage needs to access the original object.
            // - The object needs to be renamed/copied in ConfigFactory and reloaded.
            // - All instances of the object need to be renamed.
            $this->configFactory
                ->rename($prefix . $id, $config_name);
        }
        $config = $this->configFactory
            ->getEditable($config_name);
        // Retrieve the desired properties and set them in config.
        $config->setData($this->mapToStorageRecord($entity));
        $config->save($entity->hasTrustedData());
        // Update the entity with the values stored in configuration. It is possible
        // that configuration schema has casted some of the values.
        if (!$entity->hasTrustedData()) {
            $data = $this->mapFromStorageRecords([
                $config->get(),
            ]);
            $updated_entity = current($data);
            foreach (array_keys($config->get()) as $property) {
                $value = $updated_entity->get($property);
                $entity->set($property, $value);
            }
        }
        return $is_new ? SAVED_NEW : SAVED_UPDATED;
    }
    
    /**
     * Maps from an entity object to the storage record.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity object.
     *
     * @return array
     *   The record to store.
     */
    protected function mapToStorageRecord(EntityInterface $entity) {
        return $entity->toArray();
    }
    
    /**
     * {@inheritdoc}
     */
    protected function has($id, EntityInterface $entity) {
        $prefix = $this->getPrefix();
        $config = $this->configFactory
            ->get($prefix . $id);
        return !$config->isNew();
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasData() {
        return (bool) $this->configFactory
            ->listAll($this->getPrefix());
    }
    
    /**
     * {@inheritdoc}
     */
    protected function buildCacheId($id) {
        return parent::buildCacheId($id) . ':' . ($this->overrideFree ? '' : implode(':', $this->configFactory
            ->getCacheKeys()));
    }
    
    /**
     * Invokes a hook on behalf of the entity.
     *
     * @param $hook
     *   One of 'presave', 'insert', 'update', 'predelete', or 'delete'.
     * @param $entity
     *   The entity object.
     */
    protected function invokeHook($hook, EntityInterface $entity) {
        // Invoke the hook.
        $this->moduleHandler
            ->invokeAll($this->entityTypeId . '_' . $hook, [
            $entity,
        ]);
        // Invoke the respective entity-level hook.
        $this->moduleHandler
            ->invokeAll('entity_' . $hook, [
            $entity,
            $this->entityTypeId,
        ]);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getQueryServiceName() {
        return 'entity.query.config';
    }
    
    /**
     * {@inheritdoc}
     */
    public function importCreate($name, Config $new_config, Config $old_config) {
        $entity = $this->_doCreateFromStorageRecord($new_config->get(), TRUE);
        $entity->save();
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function importUpdate($name, Config $new_config, Config $old_config) {
        $id = static::getIDFromConfigName($name, $this->entityType
            ->getConfigPrefix());
        $entity = $this->load($id);
        if (!$entity) {
            throw new ConfigImporterException("Attempt to update non-existing entity '{$id}'.");
        }
        $entity->setSyncing(TRUE);
        $entity = $this->updateFromStorageRecord($entity, $new_config->get());
        $entity->save();
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function importDelete($name, Config $new_config, Config $old_config) {
        $id = static::getIDFromConfigName($name, $this->entityType
            ->getConfigPrefix());
        $entity = $this->load($id);
        $entity->setSyncing(TRUE);
        $entity->delete();
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function importRename($old_name, Config $new_config, Config $old_config) {
        return $this->importUpdate($old_name, $new_config, $old_config);
    }
    
    /**
     * {@inheritdoc}
     */
    public function createFromStorageRecord(array $values) {
        return $this->_doCreateFromStorageRecord($values);
    }
    
    /**
     * Helps create a configuration entity from storage values.
     *
     * Allows the configuration entity storage to massage storage values before
     * creating an entity.
     *
     * @param array $values
     *   The array of values from the configuration storage.
     * @param bool $is_syncing
     *   Is the configuration entity being created as part of a config sync.
     *
     * @return \Drupal\Core\Config\ConfigEntityInterface
     *   The configuration entity.
     *
     * @see \Drupal\Core\Config\Entity\ConfigEntityStorageInterface::createFromStorageRecord()
     * @see \Drupal\Core\Config\Entity\ImportableEntityStorageInterface::importCreate()
     */
    protected function _doCreateFromStorageRecord(array $values, $is_syncing = FALSE) {
        // Assign a new UUID if there is none yet.
        if ($this->uuidKey && $this->uuidService && !isset($values[$this->uuidKey])) {
            $values[$this->uuidKey] = $this->uuidService
                ->generate();
        }
        $data = $this->mapFromStorageRecords([
            $values,
        ]);
        $entity = current($data);
        $entity->original = clone $entity;
        $entity->setSyncing($is_syncing);
        $entity->enforceIsNew();
        $entity->postCreate($this);
        // Modules might need to add or change the data initially held by the new
        // entity object, for instance to fill-in default values.
        $this->invokeHook('create', $entity);
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     */
    public function updateFromStorageRecord(ConfigEntityInterface $entity, array $values) {
        $entity->original = clone $entity;
        $data = $this->mapFromStorageRecords([
            $values,
        ]);
        $updated_entity = current($data);
        
        /** @var \Drupal\Core\Config\Entity\ConfigEntityTypeInterface $entity_type */
        $entity_type = $this->getEntityType();
        $id_key = $entity_type->getKey('id');
        $properties = $entity_type->getPropertiesToExport($updated_entity->get($id_key));
        if (empty($properties)) {
            // Fallback to using the provided values. If the properties cannot be
            // determined for the config entity type annotation or configuration
            // schema.
            $properties = array_keys($values);
        }
        foreach ($properties as $property) {
            if ($property === $this->uuidKey) {
                // During an update the UUID field should not be copied. Under regular
                // circumstances the values will be equal. If configuration is written
                // twice during configuration install the updated entity will not have a
                // UUID.
                // @see \Drupal\Core\Config\ConfigInstaller::createConfiguration()
                continue;
            }
            $entity->set($property, $updated_entity->get($property));
        }
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadOverrideFree($id) {
        $entities = $this->loadMultipleOverrideFree([
            $id,
        ]);
        return isset($entities[$id]) ? $entities[$id] : NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadMultipleOverrideFree(array $ids = NULL) {
        $this->overrideFree = TRUE;
        $entities = $this->loadMultiple($ids);
        $this->overrideFree = FALSE;
        return $entities;
    }

}