import { useEffect, useRef } from 'react';
import { beginActivity } from '../../platform/activity-store';

/** What a view currently observes of a backend job; `idle` means it no longer observes one. */
export type BackendWorkState = 'idle' | 'queued' | 'running' | 'finished' | 'failed';

/**
 * Keeps one Compliance Engine activity open while backend work runs, so the activity log is not
 * `Ready` between status polls. A view that stops observing the job ends the entry with a note,
 * because the backend work itself is not cancelled.
 */
export function useBackendWorkActivity(label: string, state: BackendWorkState): void {
  const activity = useRef<ReturnType<typeof beginActivity> | undefined>(undefined);
  useEffect(() => {
    if (state === 'queued' || state === 'running') {
      activity.current ??= beginActivity('Compliance Engine', label);
      if (state === 'queued') activity.current.queue(); else activity.current.run();
      return;
    }
    const current = activity.current;
    if (!current) return;
    activity.current = undefined;
    if (state === 'failed') current.fail();
    else if (state === 'finished') current.complete();
    else detach(current, label);
  }, [label, state]);
  useEffect(() => () => {
    if (activity.current) detach(activity.current, label);
    activity.current = undefined;
  }, [label]);
}

function detach(activity: ReturnType<typeof beginActivity>, label: string) {
  activity.update(`${label} continues in the backend`);
  activity.complete();
}