class SessionManager

class SessionManager extends NativeSessionStorage implements SessionManagerInterface {
    use DependencySerializationTrait;
    
    /**
     * The request stack.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * The database connection to use.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * The session configuration.
     *
     * @var \Drupal\Core\Session\SessionConfigurationInterface
     */
    protected $sessionConfiguration;
    
    /**
     * Whether a lazy session has been started.
     *
     * @var bool
     */
    protected $startedLazy;
    
    /**
     * The write safe session handler.
     *
     * @todo: This reference should be removed once all database queries
     *   are removed from the session manager class.
     *
     * @var \Drupal\Core\Session\WriteSafeSessionHandlerInterface
     */
    protected $writeSafeHandler;
    
    /**
     * Constructs a new session manager instance.
     *
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   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 $session_configuration
     *   The session configuration interface.
     * @param \Symfony\Component\HttpFoundation\Session\Storage\Proxy\AbstractProxy|Symfony\Component\HttpFoundation\Session\Storage\Handler\NativeSessionHandler|\SessionHandlerInterface|null $handler
     *   The object to register as a PHP session handler.
     *   @see \Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage::setSaveHandler()
     */
    public function __construct(RequestStack $request_stack, Connection $connection, MetadataBag $metadata_bag, SessionConfigurationInterface $session_configuration, $handler = NULL) {
        $options = [];
        $this->sessionConfiguration = $session_configuration;
        $this->requestStack = $request_stack;
        $this->connection = $connection;
        parent::__construct($options, $handler, $metadata_bag);
        // @todo When not using the Symfony Session object, the list of bags in the
        //   NativeSessionStorage will remain uninitialized. This will lead to
        //   errors in NativeSessionHandler::loadSession. Remove this after
        //   https://www.drupal.org/node/2229145, when we will be using the Symfony
        //   session object (which registers an attribute bag with the
        //   manager upon instantiation).
        $this->bags = [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function start() {
        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 pageviews.
            $result = $this->startNow();
        }
        if (empty($result)) {
            // Randomly generate a session identifier for this request. This is
            // necessary because \Drupal\Core\TempStore\SharedTempStoreFactory::get()
            // wants to know the future session ID of a lazily started session in
            // advance.
            //
            // @todo: With current versions of PHP there is little reason to generate
            //   the session id from within application code. Consider using the
            //   default php session id instead of generating a custom one:
            //   https://www.drupal.org/node/2238561
            $this->setId(Crypt::randomBytesBase64());
            // 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() {
        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, $lifetime = NULL) {
        // Nothing to do if we are not allowed to change the session.
        if ($this->isCli()) {
            return;
        }
        // We do not support the optional $destroy and $lifetime parameters as long
        // as #2238561 remains open.
        if ($destroy || isset($lifetime)) {
            throw new \InvalidArgumentException('The optional parameters $destroy and $lifetime of SessionManager::regenerate() are not supported currently');
        }
        if ($this->isStarted()) {
            $old_session_id = $this->getId();
            // Save and close the old session. Call the parent method to avoid issue
            // with session destruction due to the session being considered obsolete.
            parent::save();
            // Ensure the session is reloaded correctly.
            $this->startedLazy = TRUE;
        }
        session_id(Crypt::randomBytesBase64());
        // We set token seed immediately to avoid race condition between two
        // simultaneous requests without a seed.
        $this->getMetadataBag()
            ->setCsrfTokenSeed(Crypt::randomBytesBase64());
        if (isset($old_session_id)) {
            $params = session_get_cookie_params();
            $expire = $params['lifetime'] ? REQUEST_TIME + $params['lifetime'] : 0;
            setcookie($this->getName(), $this->getId(), $expire, $params['path'], $params['domain'], $params['secure'], $params['httponly']);
            $this->migrateStoredSession($old_session_id);
        }
        $this->startNow();
    }
    
    /**
     * {@inheritdoc}
     */
    public function delete($uid) {
        // Nothing to do if we are not allowed to change the session.
        if (!$this->writeSafeHandler
            ->isSessionWritable() || $this->isCli()) {
            return;
        }
        $this->connection
            ->delete('sessions')
            ->condition('uid', $uid)
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function destroy() {
        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, '', REQUEST_TIME - 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);
    }
    
    /**
     * Migrates the current session to a new session id.
     *
     * @param string $old_session_id
     *   The old session ID. The new session ID is $this->getId().
     */
    protected function migrateStoredSession($old_session_id) {
        $fields = [
            'sid' => Crypt::hashBase64($this->getId()),
        ];
        $this->connection
            ->update('sessions')
            ->fields($fields)
            ->condition('sid', Crypt::hashBase64($old_session_id))
            ->execute();
    }

}