class SessionHelper

class SessionHelper {
    
    /**
     * Keep the top-level "file system" area in one place.
     */
    const SESSION_BASE_ATTRIBUTE = 'stream_wrapper_example';
    
    /**
     * Representation of the current HTTP request.
     *
     * @var \Symfony\Component\HttpFoundation\RequestStack
     */
    protected $requestStack;
    
    /**
     * This is the current location in our store.
     *
     * @var string
     */
    protected $storePath;
    
    /**
     * Construct our helper object.
     *
     * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
     *   An object used to read data from the current HTTP request.
     */
    public function __construct(RequestStack $request_stack) {
        $this->requestStack = $request_stack;
        $this->storePath = '';
    }
    
    /**
     * Get a fresh session object.
     *
     * @return \Symfony\Component\HttpFoundation\Session\SessionInterface
     *   A session object.
     */
    protected function getSession() {
        return $this->requestStack
            ->getCurrentRequest()
            ->getSession();
    }
    
    /**
     * Get the contents of the session filesystem.
     *
     * @return array
     *   An associated array where scalar data represents a file, and arrays
     *   represent directories.
     */
    protected function getStore() {
        $session = $this->getSession();
        $store = $session->get(static::SESSION_BASE_ATTRIBUTE, []);
        return $store;
    }
    
    /**
     * Set the contents of our session filesystem.
     *
     * @param array $store
     *   The whole filesystem represented as an array.
     */
    protected function setStore(array $store) {
        $session = $this->getSession();
        $session->set(static::SESSION_BASE_ATTRIBUTE, $store);
    }
    
    /**
     * Turn a path into the arrays we use internally.
     *
     * @param string $path
     *   Path into the store.
     * @param bool $is_dir
     *   Path will be used as a container. Otherwise, path is a scalar.
     *
     * @return array|bool
     *   Return an array containing the "bottom" and "tip" of a directory
     *   hierarchy.  You will want to save the 'bottom' array, but you may
     *   need to manipulate an object at the very tip of the hierarchy
     *   as defined in the path. The tip will be a string if we are scalar
     *   and an array otherwise.  Since we don't want to create new
     *   sub arrays as a side effect, we return FALSE the intervening path
     *   does not exist.
     */
    public function processPath($path, $is_dir = FALSE) {
        // We need to create a reference into the store for the point
        // the of the path, so get a copy of the store.
        $store = $this->getStore();
        if (empty($path)) {
            return [
                'store' => &$store,
                'tip' => &$store,
            ];
        }
        $hierarchy = explode('/', $path);
        if (empty($hierarchy) or empty($hierarchy[0])) {
            return [
                'store' => &$store,
                'tip' => &$store,
            ];
        }
        $bottom =& $store;
        $tip = array_pop($hierarchy);
        foreach ($hierarchy as $dir) {
            if (!isset($bottom[$dir])) {
                // If the path does not exist, DO NOT create it.
                // That is handled by the stream wrapper code.
                return FALSE;
            }
            $new_tip =& $bottom[$dir];
            $bottom =& $new_tip;
        }
        // If the hierarchy was empty, just point to the object.
        $new_tip =& $bottom[$tip];
        $bottom =& $new_tip;
        return [
            'store' => &$store,
            'tip' => &$bottom,
        ];
    }
    
    /**
     * The equivalent to dirname() and basename() for a path.
     *
     * @param string $path
     *   A file-system like path string.
     *
     * @return array
     *   Associative array defining an interal path of our data store.   .
     */
    public function getParentPath($path) {
        $dirs = explode('/', $path);
        $tip = array_pop($dirs);
        $parent = implode('/', $dirs);
        return [
            'dirname' => $parent,
            'basename' => $tip,
        ];
    }
    
    /**
     * Clear a path into our store.
     *
     * @param string $path
     *   The path portion of a URI (i.e., without the SCHEME://).
     */
    public function clearPath($path) {
        $this->getStore();
        if ($this->checkPath($path)) {
            $path_info = $this->getParentPath($path);
            $store_info = $this->processPath($path_info['dirname']);
            if ($store_info === FALSE) {
                // The path was not found, nothing to do.
                return;
            }
            // We want to clear the key at the tip, so...
            unset($store_info['tip'][$path_info['basename']]);
            // Write back to the store.
            $this->setStore($store_info['store']);
        }
    }
    
    /**
     * Get a path.
     *
     * @param string $path
     *   A URI with the SCHEME:// part removed.
     *
     * @return mixed
     *   Return the stored value at this "node" of the store.
     */
    public function getPath($path) {
        $path_info = $this->getParentPath($path);
        $store_info = $this->processPath($path_info['dirname']);
        $leaf = $path_info['basename'];
        if ($store_info === FALSE) {
            return NULL;
        }
        if ($store_info['store'] === $store_info['tip']) {
            // We are at the top of the hierarchy; return the store itself.
            if (empty($path_info['basename'])) {
                return $store_info['store'];
            }
            if (!isset($store_info['store'][$leaf])) {
                return NULL;
            }
        }
        return $store_info['tip'][$leaf];
    }
    
    /**
     * Set a path.
     *
     * @param string $path
     *   Path into the store.
     * @param string|array $value
     *   Set a value.
     */
    public function setPath($path, $value) {
        $path_info = $this->getParentPath($path);
        $store_info = $this->processPath($path_info['dirname']);
        if ($store_info !== FALSE) {
            $store_info['tip'][$path_info['basename']] = $value;
        }
        $this->setStore($store_info['store']);
    }
    
    /**
     * Does path exist?
     *
     * @param string $path
     *   Path into the store.
     *
     * @return bool
     *   Existed or not.
     */
    public function checkPath($path) {
        $path_info = $this->getParentPath($path);
        $store_info = $this->processPath($path_info['dirname']);
        if (empty($store_info)) {
            // Containing directory did not exist.
            return FALSE;
        }
        // Check if we are at the root of a directory.
        if ($path_info['basename'] === '') {
            return TRUE;
        }
        return isset($store_info['tip'][$path_info['basename']]);
    }
    
    /**
     * Zero out the store.
     */
    public function cleanUpStore() {
        $session = $this->getSession();
        $session->remove(static::SESSION_BASE_ATTRIBUTE);
    }

}