class MemoryStorage

class MemoryStorage implements StorageInterface {
  
  /**
   * The configuration, an object shared by reference across collections.
   *
   * @var \ArrayAccess
   */
  protected $config;
  
  /**
   * The storage collection.
   *
   * @var string
   */
  protected $collection;
  
  /**
   * Constructs a new MemoryStorage.
   *
   * @param string $collection
   *   (optional) The collection to store configuration in. Defaults to the
   *   default collection.
   */
  public function __construct($collection = StorageInterface::DEFAULT_COLLECTION) {
    $this->collection = $collection;
    $this->config = new \ArrayObject();
  }
  
  /**
   * {@inheritdoc}
   */
  public function exists($name) {
    return isset($this->config[$this->collection][$name]);
  }
  
  /**
   * {@inheritdoc}
   */
  public function read($name) {
    if ($this->exists($name)) {
      return $this->config[$this->collection][$name];
    }
    return FALSE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function readMultiple(array $names) {
    return array_intersect_key($this->config[$this->collection], array_flip($names));
  }
  
  /**
   * {@inheritdoc}
   */
  public function write($name, array $data) {
    $this->config[$this->collection][$name] = $data;
    return TRUE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function delete($name) {
    if (isset($this->config[$this->collection][$name])) {
      unset($this->config[$this->collection][$name]);
      // Remove the collection if it is empty.
      if (empty($this->config[$this->collection])) {
        $this->config
          ->offsetUnset($this->collection);
      }
      return TRUE;
    }
    return FALSE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function rename($name, $new_name) {
    if (!$this->exists($name)) {
      return FALSE;
    }
    $this->config[$this->collection][$new_name] = $this->config[$this->collection][$name];
    unset($this->config[$this->collection][$name]);
    return TRUE;
  }
  
  /**
   * {@inheritdoc}
   */
  public function encode($data) {
    return $data;
  }
  
  /**
   * {@inheritdoc}
   */
  public function decode($raw) {
    return $raw;
  }
  
  /**
   * {@inheritdoc}
   */
  public function listAll($prefix = '') {
    if (empty($this->config[$this->collection])) {
      // If the collection is empty no keys are set.
      return [];
    }
    $names = array_keys($this->config[$this->collection]);
    if ($prefix !== '') {
      $names = array_filter($names, function ($name) use ($prefix) {
        return strpos($name, $prefix) === 0;
      });
    }
    return $names;
  }
  
  /**
   * {@inheritdoc}
   */
  public function deleteAll($prefix = '') {
    if (!$this->config
      ->offsetExists($this->collection)) {
      // There's nothing to delete.
      return FALSE;
    }
    if ($prefix === '') {
      $this->config
        ->offsetUnset($this->collection);
      return TRUE;
    }
    $success = FALSE;
    foreach (array_keys($this->config[$this->collection]) as $name) {
      if (strpos($name, $prefix) === 0) {
        $success = TRUE;
        unset($this->config[$this->collection][$name]);
      }
    }
    // Remove the collection if it is empty.
    if (empty($this->config[$this->collection])) {
      $this->config
        ->offsetUnset($this->collection);
    }
    return $success;
  }
  
  /**
   * {@inheritdoc}
   */
  public function createCollection($collection) {
    $collection = new static($collection);
    $collection->config = $this->config;
    return $collection;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getAllCollectionNames() {
    $collection_names = [];
    foreach ($this->config as $collection_name => $data) {
      // Exclude the default collection and empty collections.
      if ($collection_name !== StorageInterface::DEFAULT_COLLECTION && !empty($data)) {
        $collection_names[] = $collection_name;
      }
    }
    sort($collection_names);
    return $collection_names;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getCollectionName() {
    return $this->collection;
  }

}