matrix-dart-sdk/lib/src/utils/markdown.dart

// @dart=2.9
/*
 *   Famedly Matrix SDK
 *   Copyright (C) 2020, 2021 Famedly GmbH
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU Affero General Public License as
 *   published by the Free Software Foundation, either version 3 of the
 *   License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 *   GNU Affero General Public License for more details.
 *
 *   You should have received a copy of the GNU Affero General Public License
 *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

import 'package:markdown/markdown.dart';
import 'dart:convert';

const htmlAttrEscape = HtmlEscape(HtmlEscapeMode.attribute);

class LinebreakSyntax extends InlineSyntax {
  LinebreakSyntax() : super(r'\n');

  @override
  bool onMatch(InlineParser parser, Match match) {
    parser.addNode(Element.empty('br'));
    return true;
  }
}

class SpoilerSyntax extends TagSyntax {
  SpoilerSyntax() : super(r'\|\|', requiresDelimiterRun: true);

  @override
  Node close(InlineParser parser, Delimiter opener, Delimiter closer,
      {List<Node> Function() getChildren}) {
    final children = getChildren();
    final newChildren = <Node>[];
    var searchingForReason = true;
    var reason = '';
    for (final child in children) {
      // If we already found a reason, let's just use our child nodes as-is
      if (!searchingForReason) {
        newChildren.add(child);
        continue;
      }
      if (child is Text) {
        final ix = child.text.indexOf('|');
        if (ix > 0) {
          reason += child.text.substring(0, ix);
          newChildren.add(Text(child.text.substring(ix + 1)));
          searchingForReason = false;
        } else {
          reason += child.text;
        }
      } else {
        // if we don't have a text node as reason we just want to cancel this whole thing
        break;
      }
    }
    // if we were still searching for a reason that means there was none - use the original children!
    final element =
        Element('span', searchingForReason ? children : newChildren);
    element.attributes['data-mx-spoiler'] =
        searchingForReason ? '' : htmlAttrEscape.convert(reason);
    return element;
  }
}

class EmoteSyntax extends InlineSyntax {
  final Map<String, Map<String, String>> Function() getEmotePacks;
  Map<String, Map<String, String>> emotePacks;
  EmoteSyntax(this.getEmotePacks) : super(r':(?:([-\w]+)~)?([-\w]+):');

  @override
  bool onMatch(InlineParser parser, Match match) {
    emotePacks ??= getEmotePacks?.call() ?? <String, Map<String, String>>{};
    final pack = match[1] ?? '';
    final emote = match[2];
    String mxc;
    if (pack.isEmpty) {
      // search all packs
      for (final emotePack in emotePacks.values) {
        mxc = emotePack[emote];
        if (mxc != null) {
          break;
        }
      }
    } else {
      mxc = emotePacks[pack] != null ? emotePacks[pack][emote] : null;
    }
    if (mxc == null) {
      // emote not found. Insert the whole thing as plain text
      parser.addNode(Text(match[0]));
      return true;
    }
    final element = Element.empty('img');
    element.attributes['data-mx-emoticon'] = '';
    element.attributes['src'] = htmlAttrEscape.convert(mxc);
    element.attributes['alt'] = htmlAttrEscape.convert(':$emote:');
    element.attributes['title'] = htmlAttrEscape.convert(':$emote:');
    element.attributes['height'] = '32';
    element.attributes['vertical-align'] = 'middle';
    parser.addNode(element);
    return true;
  }
}

class InlineLatexSyntax extends TagSyntax {
  InlineLatexSyntax() : super(r'\$([^\s$]([^\$]*[^\s$])?)\$');

  @override
  bool onMatch(InlineParser parser, Match match) {
    final element =
        Element('span', [Element.text('code', htmlEscape.convert(match[1]))]);
    element.attributes['data-mx-maths'] = htmlAttrEscape.convert(match[1]);
    parser.addNode(element);
    return true;
  }
}

// We also want to allow single-lines of like "$$latex$$"
class BlockLatexSyntax extends BlockSyntax {
  @override
  RegExp get pattern => RegExp(r'^[ ]{0,3}\$\$(.*)$');

  final endPattern = RegExp(r'^(.*)\$\$\s*$');

  @override
  List<String> parseChildLines(BlockParser parser) {
    final childLines = <String>[];
    var first = true;
    while (!parser.isDone) {
      final match = endPattern.firstMatch(parser.current);
      if (match == null || (first && match.group(1).trim().isEmpty)) {
        childLines.add(parser.current);
        parser.advance();
      } else {
        childLines.add(match.group(1));
        parser.advance();
        break;
      }
      first = false;
    }
    return childLines;
  }

  @override
  Node parse(BlockParser parser) {
    final childLines = parseChildLines(parser);
    // we use .substring(2) as childLines will *always* contain the first two '$$'
    final latex = childLines.join('\n').trim().substring(2).trim();
    final element = Element('div', [
      Element('pre', [Element.text('code', htmlEscape.convert(latex))])
    ]);
    element.attributes['data-mx-maths'] = htmlAttrEscape.convert(latex);
    return element;
  }
}

class PillSyntax extends InlineSyntax {
  PillSyntax()
      : super(
            r'([@#!][^\s:]*:(?:[^\s]+\.\w+|[\d\.]+|\[[a-fA-F0-9:]+\])(?::\d+)?)');

  @override
  bool onMatch(InlineParser parser, Match match) {
    if (match.start > 0 &&
        !RegExp(r'[\s.!?:;\(]').hasMatch(match.input[match.start - 1])) {
      parser.addNode(Text(match[0]));
      return true;
    }
    final identifier = match[1];
    final element = Element.text('a', htmlEscape.convert(identifier));
    element.attributes['href'] =
        htmlAttrEscape.convert('https://matrix.to/#/$identifier');
    parser.addNode(element);
    return true;
  }
}

class MentionSyntax extends InlineSyntax {
  final String Function(String) getMention;
  MentionSyntax(this.getMention) : super(r'(@(?:\[[^\]:]+\]|\w+)(?:#\w+)?)');

  @override
  bool onMatch(InlineParser parser, Match match) {
    final mention = getMention?.call(match[1]);
    if ((match.start > 0 &&
            !RegExp(r'[\s.!?:;\(]').hasMatch(match.input[match.start - 1])) ||
        mention == null) {
      parser.addNode(Text(match[0]));
      return true;
    }
    final element = Element.text('a', htmlEscape.convert(match[1]));
    element.attributes['href'] =
        htmlAttrEscape.convert('https://matrix.to/#/$mention');
    parser.addNode(element);
    return true;
  }
}

String markdown(
  String text, {
  Map<String, Map<String, String>> Function() getEmotePacks,
  String Function(String) getMention,
}) {
  var ret = markdownToHtml(
    text,
    extensionSet: ExtensionSet.commonMark,
    blockSyntaxes: [
      BlockLatexSyntax(),
    ],
    inlineSyntaxes: [
      StrikethroughSyntax(),
      LinebreakSyntax(),
      SpoilerSyntax(),
      EmoteSyntax(getEmotePacks),
      PillSyntax(),
      MentionSyntax(getMention),
      InlineLatexSyntax(),
    ],
  );

  var stripPTags = '<p>'.allMatches(ret).length <= 1;
  if (stripPTags) {
    const otherBlockTags = {
      'table',
      'pre',
      'ol',
      'ul',
      'h1',
      'h2',
      'h3',
      'h4',
      'h5',
      'h6',
      'blockquote',
      'div',
    };
    for (final tag in otherBlockTags) {
      // we check for the close tag as the opening one might have attributes
      if (ret.contains('</$tag>')) {
        stripPTags = false;
        break;
      }
    }
  }
  if (stripPTags) {
    ret = ret.replaceAll('<p>', '').replaceAll('</p>', '');
  }
  return ret.trim().replaceAll(RegExp(r'(<br />)+$'), '');
}