private function getHashes(array $tags)
    {
        $hashes = [];

        foreach ($tags as $tag) {
            $tag = $this->redis->prefix($tag);

            if (!$this->redis->exists($tag)) {
                continue;
            }

            $hashes = array_merge($hashes, $this->redis->smembers($tag));
        }

        return array_unique($hashes);
    }