class State

class State implements StateInterface {
  
  /**
   * The key value store to use.
   *
   * @var \Drupal\Core\KeyValueStore\KeyValueStoreInterface
   */
  protected $keyValueStore;
  
  /**
   * Static state cache.
   *
   * @var array
   */
  protected $cache = [];
  
  /**
   * Constructs a State object.
   *
   * @param \Drupal\Core\KeyValueStore\KeyValueFactoryInterface $key_value_factory
   *   The key value store to use.
   */
  public function __construct(KeyValueFactoryInterface $key_value_factory) {
    $this->keyValueStore = $key_value_factory->get('state');
  }
  
  /**
   * {@inheritdoc}
   */
  public function get($key, $default = NULL) {
    $values = $this->getMultiple([
      $key,
    ]);
    return $values[$key] ?? $default;
  }
  
  /**
   * {@inheritdoc}
   */
  public function getMultiple(array $keys) {
    $values = [];
    $load = [];
    foreach ($keys as $key) {
      // Check if we have a value in the cache.
      if (isset($this->cache[$key])) {
        $values[$key] = $this->cache[$key];
      }
      elseif (!array_key_exists($key, $this->cache)) {
        $load[] = $key;
      }
    }
    if ($load) {
      $loaded_values = $this->keyValueStore
        ->getMultiple($load);
      foreach ($load as $key) {
        // If we find a value, even one that is NULL, add it to the cache and
        // return it.
        if (isset($loaded_values[$key]) || array_key_exists($key, $loaded_values)) {
          $values[$key] = $loaded_values[$key];
          $this->cache[$key] = $loaded_values[$key];
        }
        else {
          $this->cache[$key] = NULL;
        }
      }
    }
    return $values;
  }
  
  /**
   * {@inheritdoc}
   */
  public function set($key, $value) {
    $this->cache[$key] = $value;
    $this->keyValueStore
      ->set($key, $value);
  }
  
  /**
   * {@inheritdoc}
   */
  public function setMultiple(array $data) {
    foreach ($data as $key => $value) {
      $this->cache[$key] = $value;
    }
    $this->keyValueStore
      ->setMultiple($data);
  }
  
  /**
   * {@inheritdoc}
   */
  public function delete($key) {
    $this->deleteMultiple([
      $key,
    ]);
  }
  
  /**
   * {@inheritdoc}
   */
  public function deleteMultiple(array $keys) {
    foreach ($keys as $key) {
      unset($this->cache[$key]);
    }
    $this->keyValueStore
      ->deleteMultiple($keys);
  }
  
  /**
   * {@inheritdoc}
   */
  public function resetCache() {
    $this->cache = [];
  }

}