// The inviter-name hint (#1436): a person-invite's encrypted payload carries
// the inviter's display name (`from`, beside the DM threadKey — the server
// can't open either), so the joiner's first paint can label their inviter
// instead of showing "Someone" while the instance-key grant is still in
// flight. The hint is provisional by construction: it only ever fills an
// entry whose real label hasn't decrypted, and it dies the moment one has.
// Pure decisions only — join.js/shell.js own the DOM and storage
// (Node-tested in test/invitehint.test.mjs).

export const INVITER_HINT_KEY = "lchat_inviter_hint";

// A hint outliving a week is a stale artifact of an abandoned join, not a
// first paint — and the real label has almost certainly decrypted by then.
const MAX_AGE_MS = 7 * 24 * 60 * 60 * 1000;

export function inviterHintStash({ thread, name, now }) {
  return JSON.stringify({
    v: 1,
    thread: String(thread || ""),
    name: String(name || "").trim().slice(0, 64),
    at: now,
  });
}

export function readInviterHint(storedJSON, now) {
  let h = null;
  try { h = JSON.parse(storedJSON || "null"); } catch { return null; }
  if (!h || typeof h.thread !== "string" || typeof h.name !== "string") return null;
  if (!h.thread || !h.name.trim()) return null;
  if (typeof h.at !== "number" || now < h.at || now - h.at > MAX_AGE_MS) return null;
  return { thread: h.thread, name: h.name.trim() };
}

// inviterHintTarget: who (if anyone) the hint should provisionally label.
//   { userId, name }            — fill this entry's missing label
//   { resolved: true }          — the real label decrypted; drop the stash
//   null                        — nothing to do (thread/member not loaded yet,
//                                 or the hint doesn't apply): keep the stash,
//                                 a later pass may have more data.
// Scoped hard to the hinted DM's other member — a hint must never rename
// anyone else, and never a bot (agents carry plaintext labels, never blanks).
export function inviterHintTarget(hint, threads, roster, myUserId) {
  if (!hint) return null;
  const t = (threads || []).find((x) => x && x.id === hint.thread);
  if (!t) return null;
  const otherId = (t.members || []).find((uid) => uid && uid !== myUserId);
  if (!otherId) return null;
  const e = (roster || []).find((x) => x && x.user_id === otherId);
  if (!e || e.is_agent) return null;
  if (e.label) return { resolved: true };
  return { userId: otherId, name: hint.name };
}