import {
  addDays,
  endOfMonth,
  getWeek,
  isSameWeek,
  startOfMonth,
} from "date-fns";

/**
 * Return week bounds in a [closed, open) fashion
 * The last week is not returned if it contains the next month's start date
 * @param date
 */
export function weekBoundsOfMonth(date: Date): [number, number] {
  const firstDayOfMonth = startOfMonth(date);
  const startWeek = getWeek(firstDayOfMonth);

  const lastDayOfMonth = endOfMonth(date);
  const firstDayOfNextMonth = addDays(lastDayOfMonth, 1);
  let endWeek = getWeek(lastDayOfMonth);
  if (isSameWeek(lastDayOfMonth, firstDayOfNextMonth)) endWeek -= 1;

  return [startWeek, endWeek];
}