const DAY_IN_MS = 24 * 60 * 60 * 1000;

const parseIsoDate = (dateStr) => {
  const [year, month, day] = dateStr.split("-").map(Number);
  if (!year || !month || !day) {
    return null;
  }

  return new Date(Date.UTC(year, month - 1, day));
};

export const formatDeliveryDate = (dateStr) => {
  const parsed = parseIsoDate(dateStr);
  if (!parsed) {
    return dateStr;
  }

  const day = String(parsed.getUTCDate()).padStart(2, "0");
  const month = String(parsed.getUTCMonth() + 1).padStart(2, "0");
  const year = String(parsed.getUTCFullYear());

  return `${day}.${month}.${year}`;
};

export const getDeliveryRelativeDayLabel = (dateStr, referenceDate = new Date()) => {
  const target = parseIsoDate(dateStr);
  if (!target) {
    return "";
  }

  const reference = Date.UTC(
    referenceDate.getUTCFullYear(),
    referenceDate.getUTCMonth(),
    referenceDate.getUTCDate(),
  );
  const diff = Math.round((target.getTime() - reference) / DAY_IN_MS);

  if (diff === 1) {
    return "Завтра";
  }

  if (diff === 2) {
    return "Послезавтра";
  }

  return "";
};

export const formatDeliverySlotGroupLabel = (dateStr, referenceDate = new Date()) => {
  const formattedDate = formatDeliveryDate(dateStr);
  const relativeLabel = getDeliveryRelativeDayLabel(dateStr, referenceDate);

  return relativeLabel ? `${relativeLabel} · ${formattedDate}` : formattedDate;
};

export const formatDeliverySlotLabel = ({ date, time } = {}) => {
  const formattedDate = date ? formatDeliveryDate(date) : "";

  if (!formattedDate && !time) {
    return "";
  }

  if (!formattedDate) {
    return time || "";
  }

  if (!time) {
    return formattedDate;
  }

  return `${formattedDate}, ${time}`;
};