public function getProjectRoot()
    {
        $base = '';
        $files = array_keys($this->getArrayCopy());
        $parts = explode(DIRECTORY_SEPARATOR, reset($files));

        foreach ($parts as $part) {
            $base_part = $base . $part . DIRECTORY_SEPARATOR;
            foreach ($files as $dir) {
                if (substr($dir, 0, strlen($base_part)) != $base_part) {
                    return $base;
                }
            }

            $base = $base_part;
        }

        return $base;
    }