// Serial QR requests: a refresh cannot replace a scan while its confirmation poll is still in flight.
export const SCAN_POLL_MS = 2_000;
export const SCAN_REFRESH_MS = 10_000;
export const SCAN_CONFIRM_REFRESH_MS = 60_000;

export function createQrLogin({ request, encode, onQr, onPending, onError, onConfirmed, onBusy,
  now = Date.now, timers = globalThis, isHidden = () => false }) {
  let stopped = false, completed = false, confirmed = false, active = false, busy = false, timer;
  let ready = false, awaiting = false, manual = true;
  let refreshAt = Infinity, pollAt = Infinity;
  const clear = () => { timers.clearTimeout(timer); timer = undefined; };
  const schedule = () => {
    clear();
    if (stopped || completed || !active || busy) return;
    const due = manual ? now() : ready ? Math.min(refreshAt, pollAt) : refreshAt;
    timer = timers.setTimeout(tick, isHidden() ? SCAN_POLL_MS : Math.max(0, due - now()));
  };
  const generate = async () => {
    manual = false; ready = false; awaiting = false;
    // Keep the displayed image until its replacement is encoded; refreshing only changes the existing img's src.
    onBusy(true); onPending(false); onError(null);
    try {
      const result = await request('scan/start', {});
      if (stopped) return;
      if (!result.ok || !result.scanUrl) throw new Error(result.error || 'scan_response');
      const image = await encode(result.scanUrl);
      if (stopped) return;
      ready = true; refreshAt = now() + SCAN_REFRESH_MS; pollAt = now() + SCAN_POLL_MS;
      onQr(image);
    } finally { if (!stopped) onBusy(false); }
  };
  async function tick() {
    clear();
    if (stopped || completed || !active || busy) return;
    if (isHidden()) { schedule(); return; }
    busy = true;
    try {
      if (confirmed) { manual = false; await onConfirmed(); completed = true; }
      else if (manual || !ready) await generate();
      else {
        // Poll once before an automatic refresh too: a just-scanned QR gets its full confirmation window.
        const result = await request('scan/poll', {});
        if (stopped) return;
        if (!result.ok || result.error) throw new Error(result.error || 'scan_response');
        if (result.state === 'confirmed') {
          confirmed = true; onQr(null);
          await onConfirmed();
          completed = true;
          return;
        }
        if (result.state !== 'waiting') throw new Error('scan_expired');
        if (result.awaitingConfirmation && !awaiting) {
          awaiting = true; refreshAt = now() + SCAN_CONFIRM_REFRESH_MS; onPending(true);
        }
        pollAt = now() + SCAN_POLL_MS;
        if (active && !isHidden() && (manual || now() >= refreshAt)) await generate();
      }
    } catch (error) {
      if (!stopped) {
        ready = false; refreshAt = now() + SCAN_REFRESH_MS;
        awaiting = false; onPending(false); onQr(null); onError(error);
      }
    } finally { busy = false; schedule(); }
  }
  return {
    setActive(value) { active = value; schedule(); },
    refresh() { manual = true; schedule(); },
    stop() { stopped = true; clear(); },
  };
}