public function getUnique($alias)
    {
        if (!$this->exists($alias)) {
            return $alias;
        }

        $info = pathinfo($alias);
        $ext = isset($info['extension']) ? '.' . $info['extension'] : '';

        $counter = 0;

        do {
            $counter++;
            $modified = $info['filename'] . '-' . $counter . $ext;
        } while ($this->exists($modified));

        return $modified;
    }