import { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from "react";
import { authSessionId, credentials } from "../services/authStorage";
import { onViewerChange, viewerEpoch } from "../utils/writeThroughHold";

/** Who one opening of a worklist belongs to: the viewer, acted-as subject and practice, the session and the transport. */
export interface ListOwner {
  viewer: number;
  session: string | null;
  transport: unknown;
}

/**
 * The owner of the list now shown, and whether an owner is still it. Liveness is read at the moment of asking, not from
 * the last render, so an operation begun for one viewer or session is refused for the next before the screen redraws,
 * including when the same account signs in again.
 */
export const useListOwner = (transport: unknown) => {
  const [viewer, setViewer] = useState(viewerEpoch);
  const [session, setSession] = useState(authSessionId);
  useEffect(() => {
    const changed = () => { setViewer(viewerEpoch()); setSession(authSessionId()); };
    const stop = onViewerChange(changed);
    const stopRecord = credentials().onChange(changed);
    return () => { stop(); stopRecord(); };
  }, []);
  const owner = useMemo<ListOwner>(() => ({ viewer, session, transport }), [viewer, session, transport]);
  const current = useRef<ListOwner | null>(owner);
  useLayoutEffect(() => {
    current.current = owner;
    return () => { if (current.current === owner) current.current = null; };
  }, [owner]);
  const live = useCallback((of: ListOwner) =>
    current.current === of && of.viewer === viewerEpoch() && of.session === authSessionId(), []);
  return { owner, live };
};