applyRule method

@override Delta? applyRule(Delta document, int index, { int? len, Object? data, Attribute? attribute, })

Applies heuristic rule to an operation on a document and returns resulting Delta.

Implementation

@override
Delta? applyRule(Delta document, int index, {int? len, Object? data, Attribute? attribute}) {
  if (data is! String || data != '\n') {
    return null;
  }

  final itr = DeltaIterator(document)..skip(index);
  final cur = itr.next();
  if (cur.data is! String || !(cur.data as String).startsWith('\n')) {
    return null;
  }

  Map<String, dynamic>? resetStyle;
  if (cur.attributes != null && cur.attributes!.containsKey(Attribute.header.key)) {
    resetStyle = Attribute.header.toJson();
  }
  return Delta()
    ..retain(index + (len ?? 0))
    ..insert('\n', cur.attributes)
    ..retain(1, resetStyle)
    ..trim();
}