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,
}) {
  // Only format when inserting text.
  if (data is! String) return null;

  // Get current text.
  final entireText = Document.fromDelta(document).toPlainText();

  // Get word before insertion.
  final leftWordPart = entireText
      // Keep all text before insertion.
      .substring(0, index)
      // Keep last paragraph.
      .split('\n')
      .last
      // Keep last word.
      .split(' ')
      .last
      .trimLeft();

  // Get word after insertion.
  final rightWordPart = entireText
      // Keep all text after insertion.
      .substring(index)
      // Keep first paragraph.
      .split('\n')
      .first
      // Keep first word.
      .split(' ')
      .first
      .trimRight();

  // Build the segment of affected words.
  final affectedWords = '$leftWordPart$data$rightWordPart';

  // Check for URL pattern.
  final matches = linkRegExp.allMatches(affectedWords);

  // If there are no matches, do not apply any format.
  if (matches.isEmpty) return null;

  // Build base delta.
  // The base delta is a simple insertion delta.
  final baseDelta = Delta()
    ..retain(index)
    ..insert(data);

  // Get unchanged text length.
  final unmodifiedLength = index - leftWordPart.length;

  // Create formatter delta.
  // The formatter delta will only include links formatting when needed.
  final formatterDelta = Delta()..retain(unmodifiedLength);

  var previousLinkEndRelativeIndex = 0;
  for (final match in matches) {
    // Get the size of the leading segment of text that is not part of the
    // link.
    final separationLength = match.start - previousLinkEndRelativeIndex;

    // Get the identified link.
    final link = affectedWords.substring(match.start, match.end);

    // Keep the leading segment of text and add link with its proper
    // attribute.
    formatterDelta
      ..retain(separationLength, Attribute.link.toJson())
      ..retain(link.length, LinkAttribute(link).toJson());

    // Update reference index.
    previousLinkEndRelativeIndex = match.end;
  }

  // Get remaining text length.
  final remainingLength = affectedWords.length - previousLinkEndRelativeIndex;

  // Remove links from remaining non-link text.
  formatterDelta.retain(remainingLength, Attribute.link.toJson());

  // Build and return resulting change delta.
  return baseDelta.compose(formatterDelta);
}