src/helpers/getMonthOptions.ts

import type { DateLib } from "../classes/DateLib.js";
import type { DropdownOption } from "../components/Dropdown.js";
import type { Formatters } from "../types/index.js";

/**
 * Returns the months to show in the dropdown.
 *
 * This function generates a list of months for the current year, formatted
 * using the provided formatter, and determines whether each month should be
 * disabled based on the navigation range.
 *
 * @param displayMonth The currently displayed month.
 * @param navStart The start date for navigation.
 * @param navEnd The end date for navigation.
 * @param formatters The formatters to use for formatting the month labels.
 * @param dateLib The date library to use for date manipulation.
 * @returns An array of dropdown options representing the months, or `undefined`
 *   if no months are available.
 */
export function getMonthOptions(
  displayMonth: Date,
  navStart: Date | undefined,
  navEnd: Date | undefined,
  formatters: Pick<Formatters, "formatMonthDropdown">,
  dateLib: DateLib,
): DropdownOption[] | undefined {
  const {
    startOfMonth,
    startOfYear,
    endOfYear,
    eachMonthOfInterval,
    getMonth,
  } = dateLib;

  const months = eachMonthOfInterval({
    start: startOfYear(displayMonth),
    end: endOfYear(displayMonth),
  });

  const options = months.map((month) => {
    const label = formatters.formatMonthDropdown(month, dateLib);
    const value = getMonth(month);
    const disabled =
      (navStart && month < startOfMonth(navStart)) ||
      (navEnd && month > startOfMonth(navEnd)) ||
      false;
    return { value, label, disabled };
  });

  return options;
}