import { getISOWeek, getISODay, subYears, setISOWeek, setISODay, isValid } from 'date-fns';

export const getWeekNumber = (dateString: string): number => {
  const date = new Date(dateString);
  if (!isValid(date)) {
    throw new Error('Invalid date string provided.');
  }
  return getISOWeek(date);
};

export const getSameWeekDayLastYear = (dateString: string): string => {
  const baseDate = new Date(dateString);
  if (!isValid(baseDate)) {
      throw new Error('Invalid date string provided.');
  }
  const originalWeek = getISOWeek(baseDate);
  const originalDayOfWeek = getISODay(baseDate);
  const lastYearDate = subYears(baseDate, 1);
  const dateWithWeekSet = setISOWeek(lastYearDate, originalWeek);
  const finalDate = setISODay(dateWithWeekSet, originalDayOfWeek);
  return finalDate.toISOString().split('T')[0]; // Return as YYYY-MM-DD
};