//ensures the week starts from sunday
export function weekStartSunday(date_local: Date): Date {
  const start = new Date(Date.UTC(date_local.getFullYear(), date_local.getMonth(), date_local.getDate()));
  const dow = start.getDay(); // 0 = dimanche
  start.setDate(start.getDate() - dow);
  start.setHours(0, 0, 0, 0);
  return start;
}

//converts string to HHmm format
export const toStringFromHHmm = (date: Date): string => {
  const hh = date.getUTCHours().toString().padStart(2, '0');
  const mm = date.getUTCMinutes().toString().padStart(2, '0');
  return `${hh}:${mm}`;
}

//converts string to Date format
export const toStringFromDate = (date: Date) => 
  date.toISOString().slice(0,10);



//converts HHmm format to string
export const toHHmmFromString = (hhmm: string): Date => {
  const [hh, mm] = hhmm.split(':').map(Number);
  const date = new Date('1970-01-01T00:00:00.000Z');
  date.setUTCHours(hh, mm, 0, 0);
  return new Date(date);
}

//converts string to HHmm format
export const toHHmmFromDate = (input: Date | string): string => {
    const date = new Date(input);
    const hh = String(date.getUTCHours()).padStart(2, '0');
    const mm = String(date.getUTCMinutes()).padStart(2, '0');
    return `${hh}:${mm}`;
}

//converts Date format to string
export const  toDateFromString = (ymd: string | Date): Date => {
  return new Date(`${ymd}T00:00:00:000Z`); 
}

export const toUTCDateFromString = (iso: string | Date) => {
  const d = typeof iso === 'string' ? new Date(iso + 'T00:00:00.000Z') : iso;
  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate()));
};

export const sevenDaysFrom = (date: Date | string): Date[] => {
    return Array.from({length: 7 }, (_,i) => {
        const d = new Date(date);
        d.setUTCDate(d.getUTCDate() + i );
        return d;
    });
}

export function payYearOfDate(date: string | Date, anchorISO = ANCHOR_ISO): number {
  const ANCHOR = toUTCDateFromString(anchorISO);
  const d = toUTCDateFromString(date);
  const days = Math.floor((+d - +ANCHOR) / MS_PER_DAY);
  const cycles = Math.floor(days / (PERIODS_PER_YEAR * PERIOD_DAYS));
  return ANCHOR.getUTCFullYear() + 1 + cycles;
}
//compute labels for periods
export function computePeriod(pay_year: number, period_no: number, anchorISO = ANCHOR_ISO) {
  const ANCHOR = toUTCDateFromString(anchorISO);
  const cycles = pay_year - (ANCHOR.getUTCFullYear() + 1);
  const offsetPeriods = cycles * PERIODS_PER_YEAR + (period_no - 1);
  const start = new Date(+ANCHOR + offsetPeriods * PERIOD_DAYS * MS_PER_DAY);
  const end = new Date(+start + (PERIOD_DAYS - 1) * MS_PER_DAY);
  const pay = new Date(end.getTime() + 6 * MS_PER_DAY);
  return {
    period_no: period_no,
    pay_year: pay_year,
    payday: toStringFromDate(pay),
    period_start: toStringFromDate(start),
    period_end: toStringFromDate(end),
    label: `${toStringFromDate(start)}.${toStringFromDate(end)}`,
    start, end, 
  };
}

//list of all 26 periods for a full year
export function listPayYear(pay_year: number, anchorISO = ANCHOR_ISO) {
  return Array.from({ length: PERIODS_PER_YEAR }, (_, i) => computePeriod(pay_year, i + 1, anchorISO));
}