code: protected function putInCache($key, $userId, $callId, $data, $state = self::STATE_ALIGNED)
      {
          $this->cache[$key] = [
              'userId' => $userId,
              'callId' => $callId,
              'state' => $state,
              'data' => $data
          ];
      }
docs: Puts data in the cache. Maintain the link to the userId/callId pair.
  Also keep the dirty state that will be used when persisting the data to the actual storage.
  
  @param string $key
  @param string $userId
  @param string $callId
  @param string $data
  @param int $state