impl/typescript.ts

import { type Money } from "./money_amount_types.ts";

// Money is declared in function.fune: integer minor units, never a float.

const CURRENCY = /^[A-Z]{3}$/;

export function money(minor: number, currency: string): Money {
  if (!Number.isInteger(minor)) {
    throw new TypeError(`money() takes integer minor units, received ${minor}`);
  }
  if (typeof currency !== "string" || !CURRENCY.test(currency)) {
    throw new RangeError(`"${currency}" is not an uppercase ISO 4217 currency code`);
  }
  return { minor, currency };
}

export function isMoney(value: unknown): value is Money {
  return (
    typeof value === "object" &&
    value !== null &&
    Number.isInteger((value as Money).minor) &&
    CURRENCY.test((value as Money).currency ?? "")
  );
}

/** Guard against the silent nonsense of adding GBP to EUR. */
export function assertSameCurrency(a: Money, b: Money): void {
  if (a.currency !== b.currency) {
    throw new RangeError(`currency mismatch: ${a.currency} and ${b.currency}`);
  }
}

export function zero(currency: string): Money {
  return money(0, currency);
}