react-day-picker/src/helpers/getDates.ts

Customizable Date Picker for React

import { type DateLib } from "../classes/DateLib.js";
import { type DayPickerProps } from "../types/props.js";

/** Return all the dates to display in the calendar. */
export function getDates(
  displayMonths: Date[],
  maxDate: Date | undefined,
  props: Pick<DayPickerProps, "ISOWeek" | "fixedWeeks" | "broadcastCalendar">,
  dateLib: DateLib
): Date[] {
  const firstMonth = displayMonths[0];
  const lastMonth = displayMonths[displayMonths.length - 1];

  const { ISOWeek, fixedWeeks, broadcastCalendar } = props ?? {};
  const {
    addDays,
    differenceInCalendarDays,
    differenceInCalendarMonths,
    endOfBroadcastWeek,
    endOfISOWeek,
    endOfMonth,
    endOfWeek,
    isAfter,
    startOfBroadcastWeek,
    startOfISOWeek,
    startOfWeek
  } = dateLib;

  const startWeekFirstDate = broadcastCalendar
    ? startOfBroadcastWeek(firstMonth, dateLib)
    : ISOWeek
      ? startOfISOWeek(firstMonth)
      : startOfWeek(firstMonth);

  const endWeekLastDate = broadcastCalendar
    ? endOfBroadcastWeek(lastMonth, dateLib)
    : ISOWeek
      ? endOfISOWeek(endOfMonth(lastMonth))
      : endOfWeek(endOfMonth(lastMonth));

  const nOfDays = differenceInCalendarDays(endWeekLastDate, startWeekFirstDate);
  const nOfMonths = differenceInCalendarMonths(lastMonth, firstMonth) + 1;

  const dates: Date[] = [];
  for (let i = 0; i <= nOfDays; i++) {
    const date = addDays(startWeekFirstDate, i);
    if (maxDate && isAfter(date, maxDate)) {
      break;
    }
    dates.push(date);
  }

  // If fixed weeks is enabled, add the extra dates to the array
  const nrOfDaysWithFixedWeeks = broadcastCalendar ? 35 : 42;
  const extraDates = nrOfDaysWithFixedWeeks * nOfMonths;
  if (fixedWeeks && dates.length < extraDates) {
    const daysToAdd = extraDates - dates.length;
    for (let i = 0; i < daysToAdd; i++) {
      const date = addDays(dates[dates.length - 1], 1);
      dates.push(date);
    }
  }
  return dates;
}