public function find($asset)
    {
        $asset = trim($asset, '/');
        $namespace = '/';
        while (true) {
            $file = $this->findIn($asset, $namespace);
            if (isset($file)) {
                return $file;
            }
            $pos = strpos($asset, '/');
            if ($pos === false) {
                break;
            }
            $namespace = rtrim($namespace, '/') . '/' . substr($asset, 0, $pos);
            $asset = substr($asset, $pos + 1);
        }
        return null;
    }