public function generate($date='global', Response $response=null)
    {
        if (!$response) $response = new Response;
        if ($this->maxAge) $response->setMaxAge ($this->maxAge);
        if ($this->sharedMaxAge) $response->setSharedMaxAge ($this->sharedMaxAge);
        if ($date instanceof \DateTime) {
            $response->setLastModified($date);
        } else {
            $response->setLastModified($this->manager->getLastUpdate($date));
        }

        return $response;
    }