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 { daysBetween } from "./dates_days_between.ts";  ← from dates.days-between ^1.0.0 · built alongside by fune
import { type RoundingMode, roundDiv } from "./math_round_div.ts";  ← from math.round-div ^1.0.0 · built alongside by fune
import { type Money, assertSameCurrency, money } from "./money_amount.ts";  ← from money.amount ^1.0.0 · built alongside by fune
import { type MidTermAdjustment } from "./insurance_mid_term_adjustment_types.ts";

/**
 * The additional or return premium for a change part-way through a policy term.
 *
 * The difference between the two full-term premiums is pro-rated over the
 * days left, with one rounding. Pro-rating the old and new premiums separately
 * and subtracting rounds twice and can be a penny out.
 */
export function midTermAdjustment(
  oldPremium: Money,
  newPremium: Money,
  inceptionDate: string,
  expiryDate: string,
  changeDate: string,
  adminFee: Money,
  mode: RoundingMode
): MidTermAdjustment {
  assertSameCurrency(oldPremium, newPremium);
  assertSameCurrency(oldPremium, adminFee);
  if (oldPremium.minor < 0 || newPremium.minor < 0) {
    throw new RangeError("premiums must not be negative");
  }
  if (adminFee.minor < 0) {
    throw new RangeError(`adminFee must not be negative, received ${adminFee.minor}`);
  }
  const totalDays = daysBetween(inceptionDate, expiryDate);
  if (totalDays <= 0) {
    throw new RangeError(`expiryDate must be after inceptionDate, received ${inceptionDate} to ${expiryDate}`);
  }
  const remainingDays = daysBetween(changeDate, expiryDate);
  if (remainingDays < 0 || remainingDays > totalDays) {
    throw new RangeError(`changeDate must be from inceptionDate to expiryDate, received ${changeDate}`);
  }
  const change = roundDiv((newPremium.minor - oldPremium.minor) * remainingDays, totalDays, mode);
  const currency = oldPremium.currency;
  return {
    totalDays,
    remainingDays,
    premiumChange: money(change, currency),
    adminFee,
    amountDue: money(change + adminFee.minor, currency),
    kind: change > 0 ? "additional" : change < 0 ? "return" : "none",
  };
}