interface KeyValueStoreInterface

interface KeyValueStoreInterface {
  
  /**
   * Returns the name of this collection.
   *
   * @return string
   *   The name of this collection.
   */
  public function getCollectionName();
  
  /**
   * Returns whether a given key exists in the store.
   *
   * @param string $key
   *   The key to check.
   *
   * @return bool
   *   TRUE if the key exists, FALSE otherwise.
   */
  public function has($key);
  
  /**
   * Returns the stored value for a given key.
   *
   * @param string $key
   *   The key of the data to retrieve.
   * @param mixed $default
   *   The default value to use if the key is not found.
   *
   * @return mixed
   *   The stored value, or the default value if no value exists.
   */
  public function get($key, $default = NULL);
  
  /**
   * Returns the stored key/value pairs for a given set of keys.
   *
   * @param array $keys
   *   A list of keys to retrieve.
   *
   * @return array
   *   An associative array of items successfully returned, indexed by key.
   *
   * @todo Determine the best return value for non-existing keys in
   *   https://www.drupal.org/node/2787737
   */
  public function getMultiple(array $keys);
  
  /**
   * Returns all stored key/value pairs in the collection.
   *
   * @return array
   *   An associative array containing all stored items in the collection.
   */
  public function getAll();
  
  /**
   * Saves a value for a given key.
   *
   * @param string $key
   *   The key of the data to store.
   * @param mixed $value
   *   The data to store.
   */
  public function set($key, $value);
  
  /**
   * Saves a value for a given key if it does not exist yet.
   *
   * @param string $key
   *   The key of the data to store.
   * @param mixed $value
   *   The data to store.
   *
   * @return bool
   *   TRUE if the data was set, FALSE if it already existed.
   */
  public function setIfNotExists($key, $value);
  
  /**
   * Saves key/value pairs.
   *
   * @param array $data
   *   An associative array of key/value pairs.
   */
  public function setMultiple(array $data);
  
  /**
   * Renames a key.
   *
   * @param string $key
   *   The key to rename.
   * @param string $new_key
   *   The new key name.
   */
  public function rename($key, $new_key);
  
  /**
   * Deletes an item from the key/value store.
   *
   * @param string $key
   *   The item name to delete.
   */
  public function delete($key);
  
  /**
   * Deletes multiple items from the key/value store.
   *
   * @param array $keys
   *   A list of item names to delete.
   */
  public function deleteMultiple(array $keys);
  
  /**
   * Deletes all items from the key/value store.
   */
  public function deleteAll();

}