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.contains('\n')) {
    return null;
  }

  final itr = DeltaIterator(document);
  var prev = itr.skip(len == 0 ? index : index + 1);

  if (prev == null || prev.data is! String) return null;

  if ((prev.data as String).endsWith('\n')) {
    if (prev.attributes != null) {
      for (final key in prev.attributes!.keys) {
        if (!Attribute.inlineKeys.contains(key)) {
          return null;
        }
      }
    }
    prev = itr
        .next(); // at the start of a line, apply the style for the current line and not the style for the preceding line
  }

  final attributes = prev.attributes;
  final text = data;
  if (attributes == null || !attributes.containsKey(Attribute.link.key)) {
    return Delta()
      ..retain(index + (len ?? 0))
      ..insert(text, attributes);
  }

  attributes.remove(Attribute.link.key);
  final delta = Delta()
    ..retain(index + (len ?? 0))
    ..insert(text, attributes.isEmpty ? null : attributes);
  final next = itr.next();

  final nextAttributes = next.attributes ?? const <String, dynamic>{};
  if (!nextAttributes.containsKey(Attribute.link.key)) {
    return delta;
  }
  if (attributes[Attribute.link.key] == nextAttributes[Attribute.link.key]) {
    return Delta()
      ..retain(index + (len ?? 0))
      ..insert(text, attributes);
  }
  return delta;
}