import {
  Locale,
  addYears,
  eachMonthOfInterval,
  endOfYear,
  format,
  getMonth,
  getYear,
  isBefore,
  isSameYear,
  startOfMonth,
  startOfYear,
} from "date-fns";

/** Return the months to show in the dropdown. */
export function getMonthOptions(
  displayMonth: Date,
  navStart: Date | undefined,
  navEnd: Date | undefined,
  locale: Locale,
):
  | {
      value: number;
      label: string;
      disabled: boolean;
    }[]
  | undefined {
  const months = eachMonthOfInterval({
    start: startOfYear(displayMonth),
    end: endOfYear(displayMonth),
  });

  const options = months.map((month) => {
    const label = format(month, "LLLL", { locale });
    const value = getMonth(month);
    const disabled =
      (navStart && month < startOfMonth(navStart)) ||
      (navEnd && month > startOfMonth(navEnd)) ||
      false;
    return { value, label, disabled };
  });

  return options;
}

/** Return the years to show in the dropdown. */
export function getYearOptions(
  navStart: Date | undefined,
  navEnd: Date | undefined,
  locale: Locale,
):
  | {
      value: number;
      label: string;
      disabled: boolean;
    }[]
  | undefined {
  if (!navStart) return undefined;
  if (!navEnd) return undefined;

  const firstNavYear = startOfYear(navStart);
  const lastNavYear = endOfYear(navEnd);
  const years: Date[] = [];

  let year = firstNavYear;
  while (isBefore(year, lastNavYear) || isSameYear(year, lastNavYear)) {
    years.push(year);
    year = addYears(year, 1);
  }

  return years.map((_year) => {
    const label = format(_year, "yyyy", { locale });
    return {
      value: getYear(_year),
      label,
      disabled: false,
    };
  });
}