impl/typescript.ts

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
import { type RentPeriod } from "./property_deposit_cap.ts";  ← from property.deposit-cap ^1.0.0 · built alongside by fune

// Keeps annual rent exact as a JavaScript number, with room to spare.
const MAX_MINOR = 1_000_000_000_000;

/**
 * One week's rent, the statutory maximum holding deposit: the annual rent
 * divided by 52, rounded down once so the deposit can never exceed the cap.
 */
export function holdingDepositCap(rent: Money, rentPeriod: RentPeriod): Money {
  if (rent.currency !== "GBP") {
    throw new RangeError(`rent must be in GBP, received ${rent.currency}`);
  }
  if (!Number.isInteger(rent.minor) || rent.minor < 0) {
    throw new RangeError(`rent must not be negative, received ${rent.minor}`);
  }
  let annual: number;
  if (rentPeriod === "weekly") annual = rent.minor * 52;
  else if (rentPeriod === "monthly") annual = rent.minor * 12;
  else if (rentPeriod === "annual") annual = rent.minor;
  else throw new RangeError(`unknown rent period "${rentPeriod}"`);
  if (annual > MAX_MINOR) {
    throw new RangeError(`annual rent must be at most ${MAX_MINOR} minor units`);
  }
  return money(Math.floor(annual / 52), "GBP");
}