// Reads employee names from first column of xlsx (skips header row 0)
export function readEmployeeNames(arrayBuffer) {
  const wb = XLSX.read(arrayBuffer, { type: 'array' });
  const sheet = wb.Sheets[wb.SheetNames[0]];
  const rows = XLSX.utils.sheet_to_json(sheet, { header: 1 });
  return rows.slice(1)
    .map(row => String(row[0] ?? '').trim())
    .filter(name => name.length > 0);
}

// Exports schedule as xlsx blob
// assignments: [{ date: "2026-04-01", employeeId }]
// employees: [{ id, name }]
export function exportSchedule(assignments, employees) {
  const nameById = Object.fromEntries(employees.map(e => [e.id, e.name]));
  const names = assignments.map(a => nameById[a.employeeId] ?? '');
  const dates = assignments.map(a => {
    const [y, m, d] = a.date.split('-');
    return d + '.' + m + '.' + y;
  });
  const ws = XLSX.utils.aoa_to_sheet([names, dates]);
  const wb = XLSX.utils.book_new();
  XLSX.utils.book_append_sheet(wb, ws, 'Moderationsplan');
  const buf = XLSX.write(wb, { type: 'array', bookType: 'xlsx' });
  return new Blob([buf], { type: 'application/octet-stream' });
}

export function downloadBlob(blob, filename) {
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  a.click();
  URL.revokeObjectURL(url);
}