shoedler_crossbow/src/util.ts

// Copyright (C) 2023 - shoedler - github.com/shoedler
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU 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 General Public License for more details.

// Credit: https://github.com/stiang/remove-markdown

export interface StripMarkdownOptions {
  // char to insert instead of stripped list leaders (default: '')
  listUnicodeChar?: string;
  // strip list leaders (default: true)
  stripListLeaders?: boolean;
  // support GitHub-Flavored Markdown (default: true)
  gfm?: boolean;
  // replace images with alt-text, if present (default: true)
  useImgAltText?: boolean;
  // replace abbreviations (default: false)
  abbr?: string;
  // replace links with url text (default: true)
  replaceLinksWithUrl?: boolean;
  // array of html tags to ignore (default: [])
  htmlTagsToSkip?: string[];
}

export function stripMarkdown(md: string, options?: StripMarkdownOptions) {
  options = options || {};

  options.listUnicodeChar = options.hasOwnProperty('listUnicodeChar')
    ? options.listUnicodeChar
    : undefined;
  options.stripListLeaders = options.hasOwnProperty('stripListLeaders')
    ? options.stripListLeaders
    : true;
  options.gfm = options.hasOwnProperty('gfm') ? options.gfm : true;
  options.useImgAltText = options.hasOwnProperty('useImgAltText')
    ? options.useImgAltText
    : true;
  options.abbr = options.hasOwnProperty('abbr') ? options.abbr : undefined;
  options.replaceLinksWithUrl = options.hasOwnProperty('replaceLinksWithURL')
    ? options.replaceLinksWithUrl
    : true;
  options.htmlTagsToSkip = options.hasOwnProperty('htmlTagsToSkip')
    ? options.htmlTagsToSkip
    : [];

  var output = md || '';

  // Remove horizontal rules (stripListHeaders conflict with this rule, which is why it has been moved to the top)
  output = output.replace(/^(-\s*?|\*\s*?|_\s*?){3,}\s*/gm, '');

  try {
    if (options.stripListLeaders) {
      if (options.listUnicodeChar)
        output = output.replace(
          /^([\s\t]*)([\*\-\+]|\d+\.)\s+/gm,
          options.listUnicodeChar + ' $1'
        );
      else output = output.replace(/^([\s\t]*)([\*\-\+]|\d+\.)\s+/gm, '$1');
    }
    if (options.gfm) {
      output = output
        // Header
        .replace(/\n={2,}/g, '\n')
        // Fenced codeblocks
        .replace(/~{3}.*\n/g, '')
        // Strikethrough
        .replace(/~~/g, '')
        // Fenced codeblocks
        .replace(/`{3}.*\n/g, '');
    }
    if (options.abbr) {
      // Remove abbreviations
      output = output.replace(/\*\[.*\]:.*\n/, '');
    }
    output = output
      // Remove HTML tags
      .replace(/<[^>]*>/g, '');

    var htmlReplaceRegex = new RegExp('<[^>]*>', 'g');
    if (options.htmlTagsToSkip!.length > 0) {
      // Using negative lookahead. Eg. (?!sup|sub) will not match 'sup' and 'sub' tags.
      var joinedHtmlTagsToSkip =
        '(?!' + options.htmlTagsToSkip!.join('|') + ')';

      // Adding the lookahead literal with the default regex for html. Eg./<(?!sup|sub)[^>]*>/ig
      htmlReplaceRegex = new RegExp(
        '<' + joinedHtmlTagsToSkip + '[^>]*>',
        'ig'
      );
    }

    output = output
      // Remove HTML tags
      .replace(htmlReplaceRegex, '')
      // Remove setext-style headers
      .replace(/^[=\-]{2,}\s*$/g, '')
      // Remove footnotes?
      .replace(/\[\^.+?\](\: .*?$)?/g, '')
      .replace(/\s{0,2}\[.*?\]: .*?$/g, '')
      // Remove images
      .replace(/\!\[(.*?)\][\[\(].*?[\]\)]/g, options.useImgAltText ? '$1' : '')
      // Remove inline links
      .replace(
        /\[([^\]]*?)\][\[\(].*?[\]\)]/g,
        options.replaceLinksWithUrl ? '$2' : '$1'
      )
      // Remove blockquotes
      .replace(/^\s{0,3}>\s?/gm, '')
      // .replace(/(^|\n)\s{0,3}>\s?/g, '\n\n')
      // Remove reference-style links?
      .replace(/^\s{1,2}\[(.*?)\]: (\S+)( ".*?")?\s*$/g, '')
      // Remove atx-style headers
      .replace(
        /^(\n)?\s{0,}#{1,6}\s+| {0,}(\n)?\s{0,}#{0,} #{0,}(\n)?\s{0,}$/gm,
        '$1$2$3'
      )
      // Remove * emphasis
      .replace(/([\*]+)(\S)(.*?\S)??\1/g, '$2$3')
      // Remove _ emphasis. Unlike *, _ emphasis gets rendered only if
      //   1. Either there is a whitespace character before opening _ and after closing _.
      //   2. Or _ is at the start/end of the string.
      .replace(/(^|\W)([_]+)(\S)(.*?\S)??\2($|\W)/g, '$1$3$4$5')
      // Remove code blocks
      .replace(/(`{3,})(.*?)\1/gm, '$2')
      // Remove inline code
      .replace(/`(.+?)`/g, '$1')
      // // Replace two or more newlines with exactly two? Not entirely sure this belongs here...
      // .replace(/\n{2,}/g, '\n\n')
      // // Remove newlines in a paragraph
      // .replace(/(\S+)\n\s*(\S+)/g, '$1 $2')
      // Replace strike through
      .replace(/~(.*?)~/g, '$1');
  } catch (e) {
    console.error(e);
    return md;
  }
  return output;
}