web/packages/booking-flow/lib/utils/calculateRegularPrice.ts

import type { Price } from "../types/price"

type RegularPrice = {
  pricePerStay: number
  regularPricePerStay?: number
}

// Helper function to calculate regular/strikethrough price
export function calculateRegularPrice({
  total,
  useMemberRate,
  regularMemberPrice,
  regularPublicPrice,
  additionalCost = 0,
}: {
  total: Price
  useMemberRate: boolean
  regularMemberPrice: RegularPrice | undefined
  regularPublicPrice: RegularPrice | undefined
  additionalCost?: number
}) {
  if (
    !total ||
    (!useMemberRate && !regularPublicPrice) ||
    (useMemberRate && !regularMemberPrice)
  ) {
    return total
  }

  let basePrice = 0
  // Legend:
  // - total.local.price = Total Price = Black price, what the user pays
  // - total.local.regularPrice = Regular Price = Strikethrough price (could potentially be none)
  // - total.requested.price = Requested Price = EUR approx price

  // We sometimes don't get all the required data to calculate the correct strikethrough total.
  // Therefore we try these different approach to get a number that is close
  // enough to the real number if all data would've been present.

  if (useMemberRate && regularMemberPrice) {
    if (regularPublicPrice) {
      // #1 Member price uses public price as strikethrough
      basePrice = regularPublicPrice.pricePerStay
    } else if (regularMemberPrice.regularPricePerStay) {
      // #2 Member price uses member regular price as strikethrough
      basePrice = regularMemberPrice.regularPricePerStay
    } else {
      // #3 Member price uses member price as strikethrough
      basePrice = regularMemberPrice.pricePerStay
    }
  } else if (regularPublicPrice) {
    if (regularPublicPrice.regularPricePerStay) {
      // #1 Public price uses public regular price as strikethrough
      basePrice = regularPublicPrice.regularPricePerStay
    } else {
      // #2 Public price uses public price as strikethrough
      basePrice = regularPublicPrice.pricePerStay
    }
  }

  total.local.regularPrice = add(
    total.local.regularPrice,
    basePrice,
    additionalCost
  )
  return total
}

//copied from enter-details/helpers.ts
function add(...nums: (number | string | undefined)[]) {
  return nums.reduce((total: number, num) => {
    if (typeof num === "undefined") {
      num = 0
    }
    total = total + parseInt(`${num}`)
    return total
  }, 0)
}