async function getDiscountToApply()

in handlers/discount-api/src/discountEndpoint.ts [212:279]

• 58 lines of code
• 5 McCabe index (conditional complexity)

async function getDiscountToApply(
	logger: Logger,
	stage: Stage,
	subscription: ZuoraSubscription,
	account: ZuoraAccount,
	zuoraClient: ZuoraClient,
	today: dayjs.Dayjs,
) {
	const catalog = () => getZuoraCatalog(stage);
	const eligibilityChecker = new EligibilityChecker(logger);

	// don't get the billing preview until we know the subscription is not cancelled
	const lazyBillingPreview = new Lazy(
		() =>
			getBillingPreview(
				zuoraClient,
				today.add(13, 'months'),
				subscription.accountNumber,
			),
		'get billing preview for the subscription',
	).then(billingPreviewToSimpleInvoiceItems);

	await eligibilityChecker.assertGenerallyEligible(
		subscription,
		account.metrics.totalInvoiceBalance,
		() => lazyBillingPreview.then(getNextInvoiceItems).get(),
	);

	// now we know the subscription is not cancelled we can force the billing preview
	const billingPreview = await lazyBillingPreview.get();

	logger.log('Working out the appropriate discount for the subscription');
	const { discount, discountableProductRatePlanId } =
		getDiscountFromSubscription(stage, subscription);

	logger.log('Checking this subscription is eligible for the discount');
	switch (discount.eligibilityCheckForRatePlan) {
		case 'EligibleForFreePeriod':
			eligibilityChecker.assertEligibleForFreePeriod(
				discount.productRatePlanId,
				subscription,
				today,
			);
			break;
		case 'AtCatalogPrice':
			eligibilityChecker.assertNextPaymentIsAtCatalogPrice(
				await catalog(),
				billingPreview,
				discountableProductRatePlanId,
				account.metrics.currency,
			);
			break;
		case 'NoRepeats':
			eligibilityChecker.assertNoRepeats(
				discount.productRatePlanId,
				subscription,
			);
			break;
		case 'NoCheck':
			break;
	}

	const dateToApply = getNextInvoice(billingPreview).date;

	const orderedInvoiceTotals = getOrderedInvoiceTotals(billingPreview);

	return { discount, dateToApply, orderedInvoiceTotals };
}