// Job activity adapter: prefer SSE (resumable, pushed), fall back to polling the
// same durable events when EventSource is missing or the stream errors. The cursor
// is the event `seq`, shared by both transports, so switching mid-stream never
// drops or repeats an event. subscribeJob returns a stop() handle.
import { api } from "./api.js";

// Mirrors ACTIVE_STATES in services/jobs.py; a job outside this set is terminal
// and the poller stops.
const ACTIVE = new Set(["queued", "running", "cancelling", "retry_queued"]);

export function subscribeJob(jobId, { onEvent, onDone, onError, after = 0, pollMs = 1000 } = {}) {
  let cursor = after;
  let stopped = false;
  let source = null;
  let timer = null;

  function stop() {
    if (stopped) return;
    stopped = true;
    if (source) source.close();
    if (timer) clearTimeout(timer);
    if (onDone) onDone(cursor);
  }

  async function poll() {
    if (stopped) return;
    try {
      const data = await api.jobEvents(jobId, cursor);
      for (const event of data.events) {
        cursor = event.seq;
        if (onEvent) onEvent(event);
      }
      if (!ACTIVE.has(data.state)) return stop();
    } catch (error) {
      if (!stopped && onError) onError(error);
    }
    if (!stopped) timer = setTimeout(poll, pollMs);
  }

  if (typeof EventSource === "function") {
    source = new EventSource(api.jobEventsStreamUrl(jobId, cursor));
    source.onmessage = (message) => {
      const event = JSON.parse(message.data);
      cursor = Number(message.lastEventId) || cursor;
      if (onEvent) onEvent({ seq: cursor, ...event });
    };
    // Server sends `event: done` when the job reaches a terminal state.
    source.addEventListener("done", stop);
    // Network/stream error: drop SSE and continue from the same cursor via polling
    // so no consumer notices the transport switch.
    source.onerror = () => {
      if (stopped || !source) return;
      source.close();
      source = null;
      poll();
    };
  } else {
    poll();
  }

  return { stop };
}