import { addDays, differenceInDays, parseISO, format, isBefore } from "date-fns";

export function enumerateDatePairs(startISO: string, endISO: string, minNights: number, maxNights: number, maxPairs = 8) {
  const start = parseISO(startISO);
  const end = parseISO(endISO);
  const pairs: {out: string, back: string, nights: number}[] = [];
  let cursor = start;
  while (!isBefore(end, cursor) && pairs.length < maxPairs) {
    for (let n = minNights; n <= maxNights && pairs.length < maxPairs; n++) {
      const back = addDays(cursor, n);
      if (isBefore(end, back)) continue;
      pairs.push({ out: format(cursor, "yyyyMMdd"), back: format(back, "yyyyMMdd"), nights: n });
    }
    cursor = addDays(cursor, Math.max(1, Math.floor((differenceInDays(end, start) || 1) / (maxPairs))));
  }
  if (pairs.length === 0) {
    // fallback to exact minNights from start
    const back = addDays(start, minNights);
    pairs.push({ out: format(start, "yyyyMMdd"), back: format(back, "yyyyMMdd"), nights: minNights });
  }
  return pairs;
}

export function isoToSkyscanner(iso: string) {
  return iso.replace(/-/g, "");
}