/**
 * RFC4122 v4 UUID that also works in a NON-secure context (plain `http://` on a LAN
 * IP, e.g. when localhost is unavailable), where `crypto.randomUUID` is undefined.
 *
 * Order of preference: crypto.randomUUID (secure contexts) → crypto.getRandomValues
 * (available over http too) → Math.random fallback.
 */
export function uuid(): string {
  const c: Crypto | undefined =
    typeof globalThis !== "undefined" ? (globalThis.crypto as Crypto | undefined) : undefined;

  if (c && typeof c.randomUUID === "function") {
    return c.randomUUID();
  }

  const bytes = new Uint8Array(16);
  if (c && typeof c.getRandomValues === "function") {
    c.getRandomValues(bytes);
  } else {
    for (let i = 0; i < 16; i++) bytes[i] = Math.floor(Math.random() * 256);
  }
  bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
  bytes[8] = (bytes[8] & 0x3f) | 0x80; // RFC4122 variant

  const hex = Array.from(bytes, (b) => b.toString(16).padStart(2, "0"));
  return (
    hex.slice(0, 4).join("") +
    "-" +
    hex.slice(4, 6).join("") +
    "-" +
    hex.slice(6, 8).join("") +
    "-" +
    hex.slice(8, 10).join("") +
    "-" +
    hex.slice(10, 16).join("")
  );
}
