apply method

@override Delta? apply(Delta document, int index, Object data)

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

Implementation

@override
Delta? apply(Delta document, int index, Object data) {
  // There is no other text around embeds so no inline styles to preserve.
  if (data is! String) return null;

  final text = data;

  // This rule is only applicable to characters other than newline.
  if (text.contains('\n')) return null;

  final iter = DeltaIterator(document);
  final previous = iter.skip(index);
  // If there is a newline in previous chunk, there should be no inline
  // styles. Also if there is no previous operation we are at the beginning
  // of the document so no styles to inherit from.
  if (previous == null) return null;
  final previousText =
      previous.data is String ? (previous.data as String?)! : '';
  if (previousText.contains('\n')) return null;

  final attributes = previous.attributes;
  final hasLink =
      (attributes != null && attributes.containsKey(NotusAttribute.link.key));
  if (!hasLink) {
    return Delta()
      ..retain(index)
      ..insert(text, attributes);
  }
  // Special handling needed for inserts inside fragments with link attribute.
  // Link style should only be preserved if insert occurs inside the fragment.
  // Link style should NOT be preserved on the boundaries.
  var noLinkAttributes = previous.attributes!;
  noLinkAttributes.remove(NotusAttribute.link.key);
  final noLinkResult = Delta()
    ..retain(index)
    ..insert(text, noLinkAttributes.isEmpty ? null : noLinkAttributes);
  final next = iter.next();
  final nextAttributes = next.attributes ?? const <String, dynamic>{};
  if (!nextAttributes.containsKey(NotusAttribute.link.key)) {
    // Next fragment is not styled as link.
    return noLinkResult;
  }
  // We must make sure links are identical in previous and next operations.
  if (attributes![NotusAttribute.link.key] ==
      nextAttributes[NotusAttribute.link.key]) {
    return Delta()
      ..retain(index)
      ..insert(text, attributes);
  } else {
    return noLinkResult;
  }
}