@coursebuilder/core/src/lib/pricing/parity-coupon.ts

Core package for Course Builder

import ppp from './data/ppp.js'

const DISCOUNT_UPPER_BOUND = 0.75
const DISCOUNT_LOWER_BOUND = 0.4

export function getPPPDiscountPercent(countryCode: string) {
	const ratio: number = ppp[countryCode as keyof typeof ppp]

	if (!ratio) return 0

	const percentOff = calculatePercentOff(ratio)

	if (percentOff === 0) return 0

	return percentOff
}

function calculatePercentOff(ratio: number) {
	const discount = roundTo05(1 - ratio)

	if (discount < DISCOUNT_LOWER_BOUND) return 0

	if (discount >= DISCOUNT_UPPER_BOUND) {
		return DISCOUNT_UPPER_BOUND
	}

	return discount
}

function roundTo05(decimal: number) {
	return Math.round(decimal * 20) / 20
}