// this function works as middleware
async function getSubscriber(req, res, next) {
  let subscriber
  try {
    subscriber = await Subscriber.findById(req.params.id)
    if (subscriber == null) {
      return res.status(404).json({
        message: 'Cannot find subscriber'
      })
    }
  } catch (err) {
    return res.status(500).json({
      message: err.message
    })
  }
  res.subscriber = subscriber
  next()
}