Allocate.js

/**
 * From https://v1.dinerojs.com/dinero.js
 * Allocates the amount of a Dinero object according to a list of ratios.
 *
 * Sometimes you need to split monetary values but percentages can't cut it without adding or losing pennies.
 * A good example is invoicing: let's say you need to bill $1,000.03 and you want a 50% downpayment.
 * If you use {@link module:Dinero~percentage percentage}, you'll get an accurate Dinero object but the amount won't be billable: you can't split a penny.
 * If you round it, you'll bill a penny extra.
 * With {@link module:Dinero~allocate allocate}, you can split a monetary amount then distribute the remainder as evenly as possible.
 *
 * You can use percentage style or ratio style for `ratios`: `[25, 75]` and `[1, 3]` will do the same thing.
 *
 * Since v1.8.0, you can use zero ratios (such as [0, 50, 50]). If there's a remainder to distribute, zero ratios are skipped and return a Dinero object with amount zero.
 *
 * @param  {Number[]} ratios - The ratios to allocate the money to.
 *
 * @example
 * // returns an array of two Dinero objects
 * // the first one with an amount of 502
 * // the second one with an amount of 501
 * Dinero({ amount: 1003 }).allocate([50, 50])
 * @example
 * // returns an array of two Dinero objects
 * // the first one with an amount of 25
 * // the second one with an amount of 75
 * Dinero({ amount: 100 }).allocate([1, 3])
 * @example
 * // since version 1.8.0
 * // returns an array of three Dinero objects
 * // the first one with an amount of 0
 * // the second one with an amount of 502
 * // the third one with an amount of 501
 * Dinero({ amount: 1003 }).allocate([0, 50, 50])
 *
 * @throws {TypeError} If ratios are invalid.
 *
 * @return {Dinero[]}
 */
allocate(ratios) {
  assertValidRatios(ratios)

  const total = ratios.reduce((a, b) => calculator.add(a, b))
  let remainder = this.getAmount()

  const shares = ratios.map(ratio => {
    const share = Math.floor(
      calculator.divide(calculator.multiply(this.getAmount(), ratio), total)
    )
    remainder = calculator.subtract(remainder, share)
    return create.call(this, { amount: share })
  })

  let i = 0
  while (remainder > 0) {
    if (ratios[i] > 0) {
      shares[i] = shares[i].add(create.call(this, { amount: 1 }))
      remainder = calculator.subtract(remainder, 1<)
    }
    i += 1
  }

  return shares
}