export function generateUsername(prefix = 'user') {
  const now = new Date();
  const YYYY = now.getFullYear();
  const MM = String(now.getMonth() + 1).padStart(2, '0');
  const DD = String(now.getDate()).padStart(2, '0');
  const hh = String(now.getHours()).padStart(2, '0');
  const mm = String(now.getMinutes()).padStart(2, '0');
  const ss = String(now.getSeconds()).padStart(2, '0');
  const rand = Math.random().toString(36).slice(2, 6);
  return `${prefix}${YYYY}${MM}${DD}${hh}${mm}${ss}${rand}`;
}