src/lib/currency.ts

type Currency = ('GBP' | 'USD' | 'EUR' | 'AED' | 'JOD') & string

type FormatCurrencyOptions = {
  currency: Currency
  from_minor?: boolean
  region?: string | string[] | undefined
  to_minor?: boolean
}

const getCurrencyFormatOptions = (currency: Currency) => {
  return new Intl.NumberFormat(undefined, {
    currency: currency,
    currencyDisplay: 'code',
    style: 'currency',
  }).resolvedOptions()
}

export function formatCurrency(
  number: number,
  {
    currency = 'GBP',
    from_minor,
    region = 'en-US',
    to_minor,
  }: FormatCurrencyOptions
): string {
  if (from_minor) {
    return new Intl.NumberFormat(
      region,
      getCurrencyFormatOptions(currency)
    ).format(convertCurrencyFromMinor(number, currency))
  }

  if (to_minor) {
    return new Intl.NumberFormat(
      region,
      getCurrencyFormatOptions(currency)
    ).format(convertCurrencyToMinor(number, currency))
  }

  return new Intl.NumberFormat(
    region,
    getCurrencyFormatOptions(currency)
  ).format(number)
}

const getDigits = (currency: Currency): number => {
  const digits = new Intl.NumberFormat(undefined, {
    currency,
    style: 'currency',
  }).resolvedOptions().maximumFractionDigits
  if (digits === undefined)
    throw Error(
      `[currency/getDigits] Unable to get digits for currency ${currency}`
    )

  return digits
}

export function convertCurrencyToMinor(
  amount: number,
  currency: Currency
): number {
  return Math.round(amount * 10 ** getDigits(currency))
}

export function convertCurrencyFromMinor(
  amount: number,
  currency: Currency
): number {
  return amount / 10 ** getDigits(currency)
}