update method

FlattenResult<T> update({ required List<Node<T>> data, required ViewMode mode, required Set<String>? expandedIds, })

Recomputes the visible flat list for the given inputs, reusing the cache and applying an incremental update when exactly one node's expansion changed.

Implementation

FlattenResult<T> update({
  required List<Node<T>> data,
  required ViewMode mode,
  required Set<String>? expandedIds,
}) {
  // Cache hit: nothing changed.
  if (identical(_cachedData, data) &&
      _cachedMode == mode &&
      _expandedIdsEqual(_cachedExpandedIds, expandedIds) &&
      _cachedList.isNotEmpty) {
    return FlattenResult(list: _cachedList, change: null);
  }

  // Incremental: same data/mode, exactly one node expanded or collapsed.
  if (identical(_cachedData, data) &&
      _cachedMode == mode &&
      _cachedList.isNotEmpty &&
      _cachedExpandedIds != null &&
      expandedIds != null) {
    final changedId = _singleDiff(_cachedExpandedIds!, expandedIds);
    if (changedId != null) {
      final isExpand = expandedIds.contains(changedId);
      final previousLength = _cachedList.length;
      final result = isExpand
          ? FlattenService.expandNode<T>(
              currentList: _cachedList,
              nodeId: changedId,
              expandedNodeIds: expandedIds,
            )
          : FlattenService.collapseNode<T>(
              currentList: _cachedList,
              nodeId: changedId,
            );
      if (result != null) {
        _cachedList = result.list;
        _cachedExpandedIds = Set<String>.of(expandedIds);
        return FlattenResult(
          list: _cachedList,
          change: FlattenChange(
            index: result.index,
            deltaItems: result.list.length - previousLength,
          ),
        );
      }
    }
  }

  // Full rebuild.
  final displayNodes = ViewModeProjection.project<T>(nodes: data, mode: mode);
  _cachedList = FlattenService.flatten<T>(
    nodes: displayNodes,
    expandedNodeIds: expandedIds,
  );
  _cachedData = data;
  _cachedMode = mode;
  _cachedExpandedIds =
      expandedIds != null ? Set<String>.of(expandedIds) : null;
  return FlattenResult(list: _cachedList, change: null);
}