/**
 * Period-math helpers for time-tracking.
 *
 * Lives OUTSIDE `src/actions/time-tracking/timesheets.ts` because that
 * file uses the "use server" directive, which requires every export
 * to be an async function. Pure date math doesn't need to be a server
 * action — it can run on the client too (e.g. for date pickers).
 */

/**
 * Compute the pay-period [start, end] (inclusive) that contains the
 * given date, given a brand's settings. Falls back to weekly periods
 * starting Sunday when settings aren't configured.
 */
export function payPeriodForDate(
  date: Date,
  settings: {
    pay_period_start_day: number;
    pay_period_length_days: number;
  } | null,
): { start: Date; end: Date } {
  const len = settings?.pay_period_length_days ?? 7;

  if (len === 7) {
    // Weekly — anchor to Sunday
    const start = new Date(date);
    start.setHours(0, 0, 0, 0);
    start.setDate(date.getDate() - date.getDay());
    const end = new Date(start);
    end.setDate(start.getDate() + 6);
    return { start, end };
  }

  // Semi-monthly / monthly: anchor by day-of-month
  const anchor = settings?.pay_period_start_day ?? 1;
  const start = new Date(date.getFullYear(), date.getMonth(), anchor);
  if (start > date) start.setMonth(start.getMonth() - 1);
  const end = new Date(start);
  end.setDate(start.getDate() + len - 1);
  if (end < date) {
    start.setMonth(start.getMonth() + 1);
    end.setMonth(end.getMonth() + 1);
  }
  return { start, end };
}

/** YYYY-MM-DD in UTC. */
export function toIsoDate(d: Date): string {
  return d.toISOString().slice(0, 10);
}