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 { addDays } from "./dates_add_days.ts";  ← from dates.add-days ^1.0.0 · built alongside by fune
import { type TrialPeriod } from "./subscriptions_trial_end_types.ts";

/**
 * The last free day and the first charge date of a trial of `trialDays` days
 * starting on `startDate`. The start day counts as day one, so the last free
 * day is start + trialDays - 1 and the charge is the day after it.
 */
export function trialEnd(startDate: string, trialDays: number): TrialPeriod {
  if (!Number.isInteger(trialDays)) {
    throw new TypeError(`trial days must be an integer, received ${trialDays}`);
  }
  if (trialDays < 0) {
    throw new RangeError(`trial days must not be negative, received ${trialDays}`);
  }
  // addDays validates the start date even when there is no trial, so a
  // malformed date never slips through as the "first charge date".
  const firstChargeDate = addDays(startDate, trialDays);
  const lastTrialDay = trialDays === 0 ? null : addDays(startDate, trialDays - 1);
  return { lastTrialDay, firstChargeDate };
}