flatten<T> static method

List<FlatNode<T>> flatten<T>({ required List<Node<T>> nodes, required Set<String>? expandedNodeIds, int depth = 0, bool isRoot = true, List<bool> ancestorIsLastFlags = const [], })

Flattens a tree of nodes into a list of FlatNodes, only including children of expanded nodes.

This produces the visible node list for virtualized rendering.

Implementation

static List<FlatNode<T>> flatten<T>({
  required List<Node<T>> nodes,
  required Set<String>? expandedNodeIds,
  int depth = 0,
  bool isRoot = true,
  List<bool> ancestorIsLastFlags = const [],
}) {
  final result = <FlatNode<T>>[];

  for (int i = 0; i < nodes.length; i++) {
    final node = nodes[i];
    final isFirst = i == 0;
    final isLast = i == nodes.length - 1;

    result.add(FlatNode<T>(
      node: node,
      depth: depth,
      isFirst: isFirst,
      isLast: isLast,
      isRoot: isRoot,
      ancestorIsLastFlags: ancestorIsLastFlags,
    ));

    // Recurse into children if expanded
    final isExpanded = expandedNodeIds?.contains(node.id) ?? false;
    if (isExpanded && node.children.isNotEmpty) {
      final childFlags = [...ancestorIsLastFlags, isLast];
      result.addAll(flatten<T>(
        nodes: node.children,
        expandedNodeIds: expandedNodeIds,
        depth: depth + 1,
        isRoot: false,
        ancestorIsLastFlags: childFlags,
      ));
    }
  }

  return result;
}