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

Customizable Date Picker for React

import type { DateLib } from "../classes/index.js";

/**
 * Returns the start date of the week in the broadcast calendar.
 *
 * The broadcast week starts on Monday. If the first day of the month is not a
 * Monday, this function calculates the previous Monday as the start of the
 * broadcast week.
 *
 * @since 9.4.0
 * @param date The date for which to calculate the start of the broadcast week.
 * @param dateLib The date library to use for date manipulation.
 * @returns The start date of the broadcast week.
 */
export function startOfBroadcastWeek(date: Date, dateLib: DateLib): Date {
  const firstOfMonth = dateLib.startOfMonth(date);
  const dayOfWeek = firstOfMonth.getDay();

  if (dayOfWeek === 1) {
    return firstOfMonth;
  } else if (dayOfWeek === 0) {
    return dateLib.addDays(firstOfMonth, -1 * 6);
  } else {
    return dateLib.addDays(firstOfMonth, -1 * (dayOfWeek - 1));
  }
}