Remever/lib/widgets/markdown_readmore_text.dart

import 'package:flutter/material.dart';

class MarkdownReadMoreText extends StatefulWidget {
  final String text;
  final int trimLines;
  final TextStyle style;
  final TextStyle linkStyle;
  final String expandText;
  final String collapseText;

  const MarkdownReadMoreText(
    this.text, {
    super.key,
    this.trimLines = 3,
    required this.style,
    required this.linkStyle,
    this.expandText = 'Развернуть',
    this.collapseText = 'Свернуть',
  });

  @override
  State<MarkdownReadMoreText> createState() => _MarkdownReadMoreTextState();
}

class _MarkdownReadMoreTextState extends State<MarkdownReadMoreText> {
  bool _isExpanded = false;

  @override
  Widget build(BuildContext context) {
    final spans = _parseMarkdown(widget.text);
    final fullText = TextSpan(children: spans, style: widget.style);

    return LayoutBuilder(
      builder: (context, constraints) {
        final textPainter = TextPainter(
          text: fullText,
          maxLines: widget.trimLines,
          textDirection: TextDirection.ltr,
        )..layout(maxWidth: constraints.maxWidth);

        final isOverflowed = textPainter.didExceedMaxLines;

        if (!isOverflowed) {
          return SelectableText.rich(fullText);
        }

        return Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            SelectableText.rich(
              _isExpanded ? fullText : _getTrimmedSpan(textPainter, spans),
            ),
            GestureDetector(
              onTap: () => setState(() => _isExpanded = !_isExpanded),
              child: Text(
                _isExpanded ? widget.collapseText : widget.expandText,
                style: widget.linkStyle,
              ),
            ),
          ],
        );
      },
    );
  }

  TextSpan _getTrimmedSpan(TextPainter painter, List<TextSpan> spans) {
    final trimmedText = StringBuffer();
    final remainingSpans = <TextSpan>[];

    int charCount = 0;
    final maxChars =
        painter
            .getPositionForOffset(Offset(painter.width, painter.height))
            .offset;

    for (final span in spans) {
      final spanText = span.text ?? '';
      if (charCount + spanText.length <= maxChars) {
        remainingSpans.add(span);
        charCount += spanText.length;
      } else {
        final remaining = maxChars - charCount;
        if (remaining > 0) {
          remainingSpans.add(
            TextSpan(text: spanText.substring(0, remaining), style: span.style),
          );
        }
        break;
      }
    }

    return TextSpan(children: remainingSpans, style: widget.style);
  }

  List<TextSpan> _parseMarkdown(String text) {
    final lines = text.split('\n');
    final spans = <TextSpan>[];

    for (var line in lines) {
      final trimmed = line.trim();

      // H1
      if (trimmed.startsWith('# ') && trimmed.length > 2) {
        spans.add(
          TextSpan(
            text: '${trimmed.substring(2)}\n',
            style: const TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
          ),
        );
        continue;
      }

      // Нумерованный список
      if (RegExp(r'^\d+\.\s').hasMatch(trimmed)) {
        final match = RegExp(r'^(\d+)\.\s(.+)').firstMatch(trimmed);
        if (match != null) {
          spans.add(
            TextSpan(
              text: '${match.group(0)!}\n',
              style: const TextStyle(fontSize: 16),
            ),
          );
          continue;
        }
      }

      // Маркированный список
      if (trimmed.startsWith('• ') && trimmed.length > 2) {
        spans.add(
          TextSpan(
            text: '• ${trimmed.substring(2)}\n',
            style: const TextStyle(fontSize: 16),
          ),
        );
        continue;
      }

      // Жирный текст
      final boldRegex = RegExp(r'\*\*([^*]+)\*\*');
      var remaining = line;
      var boldProcessed = <TextSpan>[];

      int lastEnd = 0;
      for (final match in boldRegex.allMatches(line)) {
        if (match.start > lastEnd) {
          boldProcessed.add(
            TextSpan(text: line.substring(lastEnd, match.start)),
          );
        }
        boldProcessed.add(
          TextSpan(
            text: match.group(1),
            style: const TextStyle(fontWeight: FontWeight.bold),
          ),
        );
        lastEnd = match.end;
      }
      if (lastEnd < line.length) {
        boldProcessed.add(TextSpan(text: line.substring(lastEnd)));
      }

      boldProcessed.add(const TextSpan(text: '\n'));
      spans.addAll(boldProcessed);
    }

    return spans;
  }
}