// Per-browser persistent client id (design/16 §4.5). Every chat message the Web
// client sends carries this id so the agent knows which browser/device the owner
// is chatting from — e.g. "web:chrome:a1b2c3". It survives reloads and is shared
// by all tabs of the same browser (localStorage), distinguishing multiple browsers
// logged into the same account.

const CLIENT_ID_KEY = "cyrene.clientId";

/** Short, human-readable browser key derived from the navigator user agent, so the
 *  deviceID reads like "chrome" rather than a raw UA string. */
function browserKey(): string {
  const ua = navigator.userAgent;
  if (/edg\//i.test(ua)) return "edge";
  if (/firefox\//i.test(ua)) return "firefox";
  if (/chrome\//i.test(ua)) return "chrome";
  if (/safari\//i.test(ua)) return "safari";
  return "browser";
}

/** Eight lowercase hex characters of random entropy (one short id token). */
function randomToken(): string {
  if (typeof crypto !== "undefined" && "getRandomValues" in crypto) {
    const bytes = new Uint8Array(4);
    crypto.getRandomValues(bytes);
    let out = "";
    for (const b of bytes) out += b.toString(16).padStart(2, "0");
    return out;
  }
  return Math.random().toString(16).slice(2, 10);
}

/** Persistent, per-browser client id: "web:<browser>:<randomToken>". Stored in
 *  localStorage so every tab of the same browser shares one id and it survives
 *  reloads. Degrades to a fresh id when localStorage is unavailable (privacy mode
 *  / a page that blocked storage): the message is still tagged, just not stable. */
export function getClientId(): string {
  const existing = localStorage.getItem(CLIENT_ID_KEY);
  if (existing && existing.startsWith("web:")) return existing;
  const id = `web:${browserKey()}:${randomToken()}`;
  try {
    localStorage.setItem(CLIENT_ID_KEY, id);
  } catch {
    // Storage unavailable: fall back to the freshly generated id for this call.
  }
  return id;
}