class SessionManager

class SessionManager extends NativeSessionStorage implements SessionManagerInterface {
    use DependencySerializationTrait;
    
    /**
     * Whether a lazy session has been started.
     *
     * @var bool
     */
    protected $startedLazy;
    
    /**
     * The write safe session handler.
     *
     * @var \Drupal\Core\Session\WriteSafeSessionHandlerInterface
     *
     * @todo This reference should be removed once all database queries
     *   are removed from the session manager class.
     */
    protected $writeSafeHandler;
    
    /**
     * Constructs a new session manager instance.
     *
     * @param \Symfony\Component\HttpFoundation\RequestStack $requestStack
     *   The request stack.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     * @param \Drupal\Core\Session\MetadataBag $metadata_bag
     *   The session metadata bag.
     * @param \Drupal\Core\Session\SessionConfigurationInterface $sessionConfiguration
     *   The session configuration interface.
     * @param \Drupal\Component\Datetime\TimeInterface $time
     *   The time service.
     * @param \Symfony\Component\HttpFoundation\Session\Storage\Proxy\AbstractProxy|\SessionHandlerInterface|null $handler
     *   The object to register as a PHP session handler.
     *
     * @see \Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage::setSaveHandler()
     */
    public function __construct(RequestStack $requestStack, Connection $connection, MetadataBag $metadata_bag, SessionConfigurationInterface $sessionConfiguration, TimeInterface $time, $handler = NULL) {
        parent::__construct([], $handler, $metadata_bag);
    }
    
    /**
     * {@inheritdoc}
     */
    public function start() : bool {
        if (($this->started || $this->startedLazy) && !$this->closed) {
            return $this->started;
        }
        $request = $this->requestStack
            ->getCurrentRequest();
        $this->setOptions($this->sessionConfiguration
            ->getOptions($request));
        if ($this->sessionConfiguration
            ->hasSession($request)) {
            // If a session cookie exists, initialize the session. Otherwise the
            // session is only started on demand in save(), making
            // anonymous users not use a session cookie unless something is stored in
            // $_SESSION. This allows HTTP proxies to cache anonymous page views.
            $result = $this->startNow();
        }
        if (empty($result)) {
            // Initialize the session global and attach the Symfony session bags.
            $_SESSION = [];
            $this->loadSession();
            // NativeSessionStorage::loadSession() sets started to TRUE, reset it to
            // FALSE here.
            $this->started = FALSE;
            $this->startedLazy = TRUE;
            $result = FALSE;
        }
        return $result;
    }
    
    /**
     * Forcibly start a PHP session.
     *
     * @return bool
     *   TRUE if the session is started.
     */
    protected function startNow() {
        if ($this->isCli()) {
            return FALSE;
        }
        if ($this->startedLazy) {
            // Save current session data before starting it, as PHP will destroy it.
            $session_data = $_SESSION;
        }
        $result = parent::start();
        // Restore session data.
        if ($this->startedLazy) {
            $_SESSION = $session_data;
            $this->loadSession();
        }
        return $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function save() : void {
        if ($this->isCli()) {
            // We don't have anything to do if we are not allowed to save the session.
            return;
        }
        if ($this->isSessionObsolete()) {
            // There is no session data to store, destroy the session if it was
            // previously started.
            if ($this->getSaveHandler()
                ->isActive()) {
                $this->destroy();
            }
        }
        else {
            // There is session data to store. Start the session if it is not already
            // started.
            if (!$this->getSaveHandler()
                ->isActive()) {
                $this->startNow();
            }
            // Write the session data.
            parent::save();
        }
        $this->startedLazy = FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function regenerate($destroy = FALSE, $lifetime = NULL) : bool {
        // Nothing to do if we are not allowed to change the session.
        if ($this->isCli()) {
            return FALSE;
        }
        // Drupal will always destroy the existing session when regenerating a
        // session. This is inline with the recommendations of @link https://cheatsheetseries.owasp.org/cheatsheets/Session_Management_Cheat_Sheet.html#renew-the-session-id-after-any-privilege-level-change
        // OWASP session management cheat sheet. @endlink
        $destroy = TRUE;
        // Cannot regenerate the session ID for non-active sessions.
        if (\PHP_SESSION_ACTIVE !== session_status()) {
            // Ensure the metadata bag has been stamped. If the parent::regenerate()
            // is called prior to the session being started it will not refresh the
            // metadata as expected.
            $this->getMetadataBag()
                ->stampNew($lifetime);
            return FALSE;
        }
        return parent::regenerate($destroy, $lifetime);
    }
    
    /**
     * {@inheritdoc}
     */
    public function delete($uid) {
        // Nothing to do if we are not allowed to change the session.
        if (!$this->writeSafeHandler
            ->isSessionWritable() || $this->isCli()) {
            return;
        }
        // The sessions table may not have been created yet.
        try {
            $this->connection
                ->delete('sessions')
                ->condition('uid', $uid)
                ->execute();
        } catch (\Exception) {
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function destroy() {
        if ($this->isCli()) {
            return;
        }
        // Symfony suggests using Session::invalidate() instead of session_destroy()
        // however the former calls session_regenerate_id(TRUE), which while
        // destroying the current session creates a new ID; Drupal has historically
        // decided to only set sessions when absolutely necessary (e.g., to increase
        // anonymous user cache hit rates) and as such we cannot use the Symfony
        // convenience method here.
        session_destroy();
        // Unset the session cookies.
        $session_name = $this->getName();
        $cookies = $this->requestStack
            ->getCurrentRequest()->cookies;
        // setcookie() can only be called when headers are not yet sent.
        if ($cookies->has($session_name) && !headers_sent()) {
            $params = session_get_cookie_params();
            setcookie($session_name, '', $this->time
                ->getRequestTime() - 3600, $params['path'], $params['domain'], $params['secure'], $params['httponly']);
            $cookies->remove($session_name);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function setWriteSafeHandler(WriteSafeSessionHandlerInterface $handler) {
        $this->writeSafeHandler = $handler;
    }
    
    /**
     * Returns whether the current PHP process runs on CLI.
     *
     * Command line clients do not support cookies nor sessions.
     *
     * @return bool
     */
    protected function isCli() {
        return PHP_SAPI === 'cli';
    }
    
    /**
     * Determines whether the session contains user data.
     *
     * @return bool
     *   TRUE when the session does not contain any values and therefore can be
     *   destroyed.
     */
    protected function isSessionObsolete() {
        $used_session_keys = array_filter($this->getSessionDataMask());
        return empty($used_session_keys);
    }
    
    /**
     * Returns a map specifying which session key is containing user data.
     *
     * @return array
     *   An array where keys correspond to the session keys and the values are
     *   booleans specifying whether the corresponding session key contains any
     *   user data.
     */
    protected function getSessionDataMask() {
        if (empty($_SESSION)) {
            return [];
        }
        // Start out with a completely filled mask.
        $mask = array_fill_keys(array_keys($_SESSION), TRUE);
        // Ignore the metadata bag, it does not contain any user data.
        $mask[$this->metadataBag
            ->getStorageKey()] = FALSE;
        // Ignore attribute bags when they do not contain any data.
        foreach ($this->bags as $bag) {
            $key = $bag->getStorageKey();
            $mask[$key] = !empty($_SESSION[$key]);
        }
        return array_intersect_key($mask, $_SESSION);
    }

}