/**
 * Creates a random RFC 4122 version 4 UUID for new entities built in the
 * browser.
 *
 * crypto.randomUUID() exists only in secure contexts (HTTPS or localhost).
 * The app is also opened over plain HTTP from other machines in the LAN, where
 * it is undefined, so fall back to crypto.getRandomValues(), which is
 * available in every context.
 */
export function createClientId(
  source: Pick<Crypto, "getRandomValues"> & Partial<Pick<Crypto, "randomUUID">> = crypto
): string {
  if (typeof source.randomUUID === "function") {
    return source.randomUUID();
  }
  const bytes = source.getRandomValues(new Uint8Array(16));
  bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
  bytes[8] = (bytes[8] & 0x3f) | 0x80; // RFC 4122 variant
  const hex = Array.from(bytes, (byte) => byte.toString(16).padStart(2, "0")).join("");
  return [
    hex.slice(0, 8),
    hex.slice(8, 12),
    hex.slice(12, 16),
    hex.slice(16, 20),
    hex.slice(20),
  ].join("-");
}