collapseNode<T> static method

({int index, List<FlatNode<T>> list})? collapseNode<T>({ required List<FlatNode<T>> currentList, required String nodeId, })

Incrementally collapse a node: remove all descendants that follow it.

Mutates currentList in place (caller-owned) to avoid copying the whole list, and returns that same list with the index of the collapsed node. Returns null if the node was not found (caller should fall back to a full rebuild).

Implementation

static ({List<FlatNode<T>> list, int index})? collapseNode<T>({
  required List<FlatNode<T>> currentList,
  required String nodeId,
}) {
  final idx = currentList.indexWhere((fn) => fn.node.id == nodeId);
  if (idx == -1) return null;

  final parentDepth = currentList[idx].depth;

  // Find the end of descendants: all consecutive items with depth > parentDepth
  int endIdx = idx + 1;
  while (endIdx < currentList.length &&
      currentList[endIdx].depth > parentDepth) {
    endIdx++;
  }

  if (endIdx == idx + 1) {
    return (list: currentList, index: idx); // Nothing to remove
  }

  // Remove the descendant range in place.
  currentList.removeRange(idx + 1, endIdx);
  return (list: currentList, index: idx);
}