Stripe Usage Reporting

// Listening on the webhook endpoint
export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  if (req.method !== "POST") {
    res.status(405).json({});
    return;
  }
  const idempotencyKey = req.headers["svix-id"];
  const msg = (await buffer(req)).toString();

  // See webhooks docs about how to verify signatures
  if (msg.type === "report.meter") {
    await reportusageToStripe(idempotencyKey, msg);
    return res.status({});
  }

  res.status(400).json({ message: "Unknown event type" });
  return;
}

function reportusageToStripe(idempotencyKey, msg) {
  const { usage, meter, query } = msg;

  // Find stripe subscription ID for subject (customer)
  // usually a databse call in your application
  const stripeSubscriptionId = getSubscriptionIdForSubject(query.subject)

  // Find stripe subscription item for meter
  const subscriptionItems = await stripe.subscriptionItems.list({
    subscription: stripeSubscriptionId
  });

  for (const { value, windowEnd } in msg.usage) {
    const subscriptionItem = subscriptionItems.find(({ price }) =>
      // retreive stripe price id for meter (usually from config)
      price.id === getPriceIdForMeter(meter.slug)
    )

    // Report usage to Stripe
    await stripe.subscriptionItems.createUsageRecord(
      subscriptionItem.id,
      {
        quantity: value,
        timestamp: windowend,
        action: 'set'
      },
      {
        idempotencyKey,
      }
    );
  }
}