export const TreeLoadChildrenMixin = (superClass) => class TreeLoadChildrenMixin extends superClass {
  async _loadChildrenForExpanded(key, source, originalEvent, nodeHint = null, pathHint = null) {
    if (typeof this.loadChildren !== 'function') return;

    const node = nodeHint ?? this._findNodeByKey(key);
    if (!node) return;

    const controller = new AbortController();
    const seq = ++this._childLoadSeq;
    const previous = this._childLoadControllers.get(key);
    if (previous) {
      try { previous.abort(); } catch (e) { }
    }
    this._childLoadControllers.set(key, controller);

    this._updateNodeStatesByKey(key, (n) => {
      const states = Array.isArray(n.states) ? n.states : [];
      const next = states.filter((s) => s !== 'loaded');
      if (!next.includes('loading')) next.push('loading');
      return { ...n, states: next };
    });

    try {
      const ctx = {
        node,
        key,
        path: Array.isArray(pathHint) ? pathHint : key.split('/').filter(Boolean),
        signal: controller.signal,
        source,
        originalEvent,
      };

      await Promise.resolve(this.loadChildren(ctx));
      if (controller.signal.aborted) return;
      if (this._childLoadControllers.get(key) !== controller) return;
      if (seq !== this._childLoadSeq) return;

      this._updateNodeStatesByKey(key, (n) => {
        const states = Array.isArray(n.states) ? n.states : [];
        const next = states.filter((s) => s !== 'loading');
        if (!next.includes('loaded')) next.push('loaded');
        return { ...n, states: next };
      });
    } catch (err) {
      if (controller.signal.aborted) return;
      this._updateNodeStatesByKey(key, (n) => {
        const states = Array.isArray(n.states) ? n.states : [];
        const next = states.filter((s) => s !== 'loading');
        return { ...n, states: next };
      });
      this.dispatchEvent(new CustomEvent('node-children-error', {
        detail: { key, node, error: err, source, originalEvent },
        bubbles: true,
        composed: true,
      }));
    } finally {
      if (this._childLoadControllers.get(key) === controller) {
        this._childLoadControllers.delete(key);
      }
    }
  }
};