// Copyright (c) 2026 Patrick Motsch
// All rights reserved.
/**
 * useTreeExpansion - fire-and-forget persistence for tree expand state.
 *
 * Simple contract:
 *   - On mount: load saved expandedIds from backend (or null if none).
 *   - Returns the loaded ids (once) so the tree can seed its initial state.
 *   - Provides a `save(ids)` function that debounce-PUTs to the backend.
 *   - No bidirectional state flow, no props, no re-render triggers.
 */

import { useCallback, useEffect, useRef, useState } from 'react';
import api from '../api';

const _SAVE_DEBOUNCE_MS = 600;

export interface UseTreeExpansionResult {
  loaded: boolean;
  initialIds: string[] | null;
  save: (ids: string[]) => void;
}

export function useTreeExpansion(
  instanceId: string | null | undefined,
  scope: string,
): UseTreeExpansionResult {
  const [loaded, setLoaded] = useState(false);
  const [initialIds, setInitialIds] = useState<string[] | null>(null);
  const saveTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
  const latestRef = useRef<string[] | null>(null);

  useEffect(() => {
    if (!instanceId) {
      setLoaded(true);
      setInitialIds(null);
      return;
    }
    let cancelled = false;
    setLoaded(false);
    api
      .get(`/api/workspace/${instanceId}/ui-tree-expansion/${encodeURIComponent(scope)}`)
      .then((res) => {
        if (cancelled) return;
        const fromServer: string[] | null = res.data?.expandedNodes ?? null;
        setInitialIds(fromServer);
        latestRef.current = fromServer;
        setLoaded(true);
      })
      .catch((err) => {
        if (cancelled) return;
        console.warn('[useTreeExpansion] load failed', err);
        setInitialIds(null);
        setLoaded(true);
      });
    return () => { cancelled = true; };
  }, [instanceId, scope]);

  const save = useCallback(
    (ids: string[]) => {
      if (!instanceId) return;
      const sorted = [...ids].sort().join('|');
      const prevSorted = latestRef.current ? [...latestRef.current].sort().join('|') : null;
      if (sorted === prevSorted) return;
      latestRef.current = ids;
      if (saveTimerRef.current) clearTimeout(saveTimerRef.current);
      saveTimerRef.current = setTimeout(() => {
        api
          .put(
            `/api/workspace/${instanceId}/ui-tree-expansion/${encodeURIComponent(scope)}`,
            { expandedNodes: latestRef.current ?? [] },
          )
          .catch((err) => {
            console.warn('[useTreeExpansion] save failed', err);
          });
      }, _SAVE_DEBOUNCE_MS);
    },
    [instanceId, scope],
  );

  useEffect(() => {
    return () => {
      if (saveTimerRef.current) clearTimeout(saveTimerRef.current);
    };
  }, []);

  return { loaded, initialIds, save };
}