/**
 * Generates a UUID v4.
 * Falls back to a manual implementation when crypto.randomUUID is unavailable
 * (HTTP non-secure contexts, older browsers).
 */
export function generateUUID(): string {
  if (typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function') {
    return crypto.randomUUID()
  }
  // Fallback: RFC 4122 v4 UUID using crypto.getRandomValues if available
  if (typeof crypto !== 'undefined' && typeof crypto.getRandomValues === 'function') {
    const bytes = new Uint8Array(16)
    crypto.getRandomValues(bytes)
    bytes[6] = (bytes[6] & 0x0f) | 0x40
    bytes[8] = (bytes[8] & 0x3f) | 0x80
    return [...bytes]
      .map((b, i) => ([4, 6, 8, 10].includes(i) ? '-' : '') + b.toString(16).padStart(2, '0'))
      .join('')
  }
  // Last resort: Math.random based (not cryptographically secure)
  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
    const r = (Math.random() * 16) | 0
    return (c === 'x' ? r : (r & 0x3) | 0x8).toString(16)
  })
}