// Initialize the agent
const fpPromise = import('https://fpjscdn.net/v3/your-public-api-key')
  .then(FingerprintJS => FingerprintJS.load({
    endpoint: 'https://fp.yourdomain.com'
  }));

// Once you need result, get and store it.
// Typically on page load or on button click.
fpPromise
  .then(fp => fp.get())
  .then(fpResult => {result = fpResult})

const couponData = {
  visitorId,
  requestId,
	couponId
};

const response = await fetch(`/api/checkout/coupons}`, {
  method: 'POST',
  body: JSON.stringify(fingerprintData),
  headers: {
    'Content-Type': 'application/json',
    Accept: 'application/json',
  },
});

const visitorId = req.body.visitorId;
const requestId = req.body.requestId;

const isRequestIdFormatValid = /^\d{13}\.[a-zA-Z0-9]{6}$/.test(requestId);
const isVisitorIdFormatValid = /^[a-zA-Z0-9]{20}$/.test(visitorId);

if (!isRequestIdFormatValid || !isVisitorIdFormatValid) {
  return getForbiddenReponse();
}

const fingerprintJSProServerApiUrl = new URL(
  `https://api.fpjs.io/visitors/${visitorId}`
);

fingerprintJSProServerApiUrl.searchParams.append('request_id', requestId);

const visitorServerApiResponse = await fetch(
  fingerprintJSProServerApiUrl.href, { method: 'GET', headers: { 'Auth-API-Key': 'secret-api-key' } }
);

// If there's something wrong with provided data, Server API might return non 200 response.
// We consider these data unreliable.
if (visitorServerApiResponse.status !== 200) {
	reportSuspiciousActivity(req);
  // Handle error internaly, do not allow the coupon code to be applied.
}

const visitorData = await visitorServerApiResponse.json();
return visitorData;

if (visitorData.error || visitorData.visits.length !== 1) {
	// Do not allow the coupon code to be applied.
  return getForbiddenReponse();
}

if (new Date().getTime() - visitorData.visits[0].timestamp > 3000) {
	// Do not allow the coupon code to be applied.
  return getForbiddenReponse();
}

// This is an example of obtaining the client IP address.
// In most cases, it's a good idea to look for the right-most external IP address in the list to prevent spoofing.
if (
  request.headers['x-forwarded-for'].split(',')[0] !==
  visitorData.visits[0].ip
) {
	// Do not allow the coupon code to be applied.
  return getForbiddenReponse();
}

const ourOrigins = [
  'https://example.com',
];

const visitorDataOrigin = new URL(visitorData.visits[0].url).origin;
if (
  (visitorDataOrigin !== request.headers['origin'] ||
    !ourOrigins.includes(visitorDataOrigin) ||
    !ourOrigins.includes(request.headers['origin']))
) {
	// Do not allow the coupon code to be applied.
  return getForbiddenReponse();
}

/**
 * Checks if a coupon exists with the given coupon code.
 */
export async function checkCoupon(code) {
  return await CouponCode.findOne({
    where: {
      code: {
        [Op.eq]: code,
      },
    },
  });
}

async function getVisitorClaim(visitorId, couponCode) {
  return await CouponClaim.findOne({
    where: { visitorId, couponCode },
  });
}

const coupon = await checkCoupon(couponCode);

// Check if the coupon exists.
if (!coupon) {
  return getForbiddenReponse(res, 'Provided coupon code does not exist.', 'error');
}

const wasCouponClaimedByVisitor = await getVisitorClaim(visitorId, couponCode);

async function checkVisitorClaimedRecently(visitorId) {
  const oneHourBefore = new Date();
  oneHourBefore.setHours(oneHourBefore.getHours() - 1);

  return await CouponClaim.findOne({
    where: {
      visitorId,
      timestamp: {
        [Op.between]: [oneHourBefore, new Date()],
      },
    },
  });
}

/**
 * Claim coupon on behalf of the visitor.
 */
export async function claimCoupon(visitorId, couponCode) {
  const claim = await CouponClaim.create({
    couponCode,
    visitorId,
    timestamp: new Date(),
  });
  await claim.save();

  return claim;
}

const visitorClaimedAnotherCouponRecently = await checkVisitorClaimedRecently(visitorId);

if (visitorClaimedAnotherCouponRecently) {
  return getForbiddenReponse(res, 'The visitor claimed another coupon recently.\n', 'error');
}

await claimCoupon(visitorId, couponCode);

return getOkReponse(res, `Coupon claimed you get a 119 USD discount!`, 'success');