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 = [];
    }

}