export function loadFromJSON(json) {
  let parsed;
  try {
    parsed = JSON.parse(json);
  } catch (e) {
    throw new Error('Ungültige JSON-Datei: ' + e.message);
  }
  if (typeof parsed !== 'object' || parsed === null) {
    throw new Error('Ungültiges Dateiformat: Objekt erwartet');
  }
  return {
    employees: Array.isArray(parsed.employees) ? parsed.employees : [],
    calendar: (parsed.calendar && typeof parsed.calendar === 'object')
      ? {
          holidays: Array.isArray(parsed.calendar.holidays) ? parsed.calendar.holidays : [],
          companyClosures: Array.isArray(parsed.calendar.companyClosures) ? parsed.calendar.companyClosures : []
        }
      : { holidays: [], companyClosures: [] },
    history: Array.isArray(parsed.history) ? parsed.history : []
  };
}

export function saveToJSON(state) {
  return JSON.stringify({
    employees: state.employees,
    calendar: state.calendar,
    history: state.history
  }, null, 2);
}

export function createEmployee(name) {
  const trimmed = (name ?? '').trim();
  if (!trimmed) throw new Error('Mitarbeitername darf nicht leer sein');
  return {
    id: crypto.randomUUID(),
    name: trimmed,
    constraints: {
      neverDays: [],
      lowPriorityDays: [],
      onlyDays: [],
      maxPerMonth: null,
      minGapDays: 0,
      vacations: []
    }
  };
}

export function removeEmployee(state, id) {
  state.employees = state.employees.filter(e => e.id !== id);
}

export function toggleHoliday(state, isoDate) {
  const arr = state.calendar.holidays;
  const idx = arr.indexOf(isoDate);
  if (idx >= 0) arr.splice(idx, 1); else arr.push(isoDate);
}

export function toggleClosure(state, isoDate) {
  const arr = state.calendar.companyClosures;
  const idx = arr.indexOf(isoDate);
  if (idx >= 0) arr.splice(idx, 1); else arr.push(isoDate);
}

// Adds entries to history, replacing any existing entries for the same dates
export function addHistoryEntries(state, entries) {
  if (!entries?.length) return;
  const dates = new Set(entries.map(e => e.date));
  state.history = state.history.filter(h => !dates.has(h.date));
  state.history.push(...entries);
  state.history.sort((a, b) => a.date.localeCompare(b.date));
}

export function removeHistoryEntry(state, isoDate) {
  state.history = state.history.filter(h => h.date !== isoDate);
}