frontend/src/lib/daemon.ts

// Poll the local daemon for real wire events. Offline-tolerant by design:
// the sim is fully alive without a daemon, so failures are silent and the
// poll backs off until the daemon answers again.

import { isWireEvent, type WireEvent } from "../engine";

const POLL_MS = 3000;
const OFFLINE_BACKOFF_MS = 15000;

export function startDaemonPoll(onEvents: (events: WireEvent[]) => void): () => void {
  let timer: ReturnType<typeof setTimeout> | undefined;
  let stopped = false;

  const tick = async () => {
    if (stopped) return; // unmounted before first tick — never drain for a dead poller
    let delay = POLL_MS;
    try {
      const res = await fetch("/api/events/pending", { signal: AbortSignal.timeout(2000) });
      if (res.ok) {
        const body: unknown = await res.json();
        const list = (body as { events?: unknown[] }).events ?? [];
        const valid = list.filter(isWireEvent);
        // a malformed event on this path means the daemon let contract drift through — be loud
        if (valid.length !== list.length)
          console.error("puck: daemon sent events violating the wire schema", list);
        // drain is destructive — a stopped poller (StrictMode's first mount) must not
        // swallow events meant for the live one. Losing one drain to an unlucky unmount
        // race is acceptable; silently eating every event on dev double-mount is not.
        if (valid.length && !stopped) onEvents(valid);
      } else {
        delay = OFFLINE_BACKOFF_MS;
      }
    } catch {
      delay = OFFLINE_BACKOFF_MS; // daemon not running — normal in Space/demo mode
    }
    if (!stopped) timer = setTimeout(tick, delay);
  };

  // drain is destructive, so the first fetch must not race React StrictMode's
  // mount→unmount→mount: the doomed first instance is cleaned up synchronously,
  // well inside this delay, so only the surviving poller ever touches the queue.
  timer = setTimeout(tick, 350);
  return () => {
    stopped = true;
    clearTimeout(timer);
  };
}