export function calculateHours(startTime, endTime) {
  if (!startTime || !endTime) return 0;
  if (endTime === "manual") return parseFloat(startTime) || 0;

  const parseTime = (timeStr) => {
    const parts = timeStr.split(":");
    if (parts.length !== 2) return 0;
    return parseFloat(parts[0]) + parseFloat(parts[1]) / 60;
  };

  const start = parseTime(startTime);
  const end = parseTime(endTime);

  if (end > start) return end - start;
  return 0;
}

export function getISOWeek(date) {
  const d = new Date(
    Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()),
  );
  const dayNum = d.getUTCDay() || 7;
  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
  const yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
  return Math.ceil(((d - yearStart) / 86400000 + 1) / 7);
}

export function getISOYear(date) {
  const d = new Date(
    Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()),
  );
  const dayNum = d.getUTCDay() || 7;
  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
  return d.getUTCFullYear();
}

export function getDateOfISOWeek(w, y) {
  const simple = new Date(y, 0, 1 + (w - 1) * 7);
  const dow = simple.getDay();
  const ISOweekStart = simple;
  if (dow <= 4) ISOweekStart.setDate(simple.getDate() - simple.getDay() + 1);
  else ISOweekStart.setDate(simple.getDate() + 8 - simple.getDay());
  return ISOweekStart;
}

export function formatDate(date) {
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, "0");
  const day = String(date.getDate()).padStart(2, "0");
  return `${year}-${month}-${day}`;
}

export const dayNames = [
  "Montag",
  "Dienstag",
  "Mittwoch",
  "Donnerstag",
  "Freitag",
];