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

export const daysOfWeek = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];

/**
 * 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): [Date, Date] {
  const firstDayOfMonth = startOfMonth(date);
  const startWeek = startOfWeek(firstDayOfMonth);

  const lastDayOfMonth = endOfMonth(date);
  const firstDayOfNextMonth = addDays(lastDayOfMonth, 1);
  let endWeek = startOfWeek(lastDayOfMonth);

  if (isSameWeek(lastDayOfMonth, firstDayOfNextMonth))
    endWeek = subDays(endWeek, 7);

  return [startWeek, endWeek];
}

export function weekString(date: Date): string {
  return `${getWeek(date)}/${date.getFullYear()}`;
}

export function monthNameOf(date: Date): string {
  return date.toLocaleDateString("default", { month: "long" });
}