money.split-even

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

import { type Money, money } from "./money_amount.ts";  ← from money.amount ^1.0.0 · built alongside by fune

/**
 * Split `amount` into `parts` near-equal shares that sum to exactly `amount`.
 *
 * The leftover minor units go one each to the first shares, and a negative
 * amount splits as the mirror image of the positive one, so a refund undoes
 * the original split share for share.
 */
export function splitEven(amount: Money, parts: number): readonly Money[] {
  if (!Number.isInteger(parts)) {
    throw new TypeError(`parts must be a whole number, received ${parts}`);
  }
  if (parts < 1) {
    throw new RangeError(`parts must be at least 1, received ${parts}`);
  }
  const sign = amount.minor < 0 ? -1 : 1;
  const magnitude = Math.abs(amount.minor);
  const base = Math.floor(magnitude / parts);
  const leftover = magnitude - base * parts;

  const shares: Money[] = [];
  for (let i = 0; i < parts; i++) {
    const share = base + (i < leftover ? 1 : 0);
    // `0 * -1` is -0 in JavaScript; keep zero shares plain zero.
    shares.push(money(share === 0 ? 0 : sign * share, amount.currency));
  }
  return shares;
}