Flutter expandable text step 3

expandable_5.dart

class _ExpandableTextState extends State<ExpandableText> {
  static const String _ellipsis = "\u2026\u0020";

  String get _lineEnding => "$_ellipsis${widget.moreSpan.text}";
// ...

  @override
  Widget build(BuildContext context) => LayoutBuilder(
        builder: (context, constraints) {
          final maxLines = widget.maxLines;

          final richText = Text.rich(widget.textSpan).build(context) as RichText;
          final boxes = richText.measure(context, constraints);

          if (boxes.length <= maxLines || _isExpanded) {
            return RichText(text: widget.textSpan);
          } else {
            final croppedText = _ellipsizeText(boxes);
            final ellipsizedText = _buildEllipsizedText(croppedText, _tapRecognizer);

            if (ellipsizedText.measure(context, constraints).length <= maxLines) {
              return ellipsizedText;
            } else {
              final fixedEllipsizedText = croppedText.substring(0, croppedText.length - _lineEnding.length);
              return _buildEllipsizedText(fixedEllipsizedText, _tapRecognizer);
            }
          }
        },
      );

  String _ellipsizeText(List<TextBox> boxes) {
    final text = widget.textSpan.text;
    final maxLines = widget.maxLines;

    double _calculateLinesLength(List<TextBox> boxes) => boxes.map((box) => box.right - box.left).reduce((acc, value) => acc += value);

    final requiredLength = _calculateLinesLength(boxes.sublist(0, maxLines));
    final totalLength = _calculateLinesLength(boxes);

    final requiredTextFraction = requiredLength / totalLength;
    return text.substring(0, (text.length * requiredTextFraction).floor());
  }

  RichText _buildEllipsizedText(String text, GestureRecognizer tapRecognizer) => RichText(
        text: TextSpan(
          text: "$text$_ellipsis",
          style: widget.textSpan.style,
          children: [widget.moreSpan],
        ),
      );
}