Convert Telegram message entities to MarkdownV2

parse-md.js

/*
  @parseMD function: convert Telegram message entities to MarkdownV2
  Based on: https://github.com/butthx/duckbot/blob/036b1681c1a55132490a59a5cc9dea53006d0c99/src/modules/misc.ts#L1456
  Especial thanks ♥ to: https://github.com/butthx
 */
function parseMD (text = '', entities = []) {
  if (entities.length === 0) return text;
  let cache = [];
  const res = [];
  const styles = {
    bold: '*',
    code: '`',
    italic: '_',
    pre: '```',
    strikethrough: '~',
    underline: '__'
  };
  for (const [i, el] of [...text].entries()) {
    while (entities.length > 0) {
      const x = entities.findIndex(a => a.offset === i);
      if (x === -1) break;
      const { type } = entities[x];
      if (!['text_mention', 'text_link', 'pre'].includes(type)) res.push(styles[type]);
      else if (type === 'pre') {
        if (entities[x].language) res.push(`${styles[type]}${entities[x].language}\n`);
        else res.push(styles[type]);
      } else if (['text_mention', 'text_link'].includes(type)) res.push('[');
      cache = [entities[x], ...cache];
      entities.splice(x, 1);
    }
    res.push(el.replace(/[!#()*+.=>[\]_`{|}~-]/g, '\\$&'));
    while (cache.length > 0) {
      const y = cache.findIndex(b => b.offset + b.length - 1 === i);
      if (y === -1) break;
      const { type } = cache[y];
      if (!['text_mention', 'text_link'].includes(type)) res.push(styles[type]);
      else if (type === 'text_mention') res.push(`](tg://user?id=${cache[y].user.id})`);
      else if (type === 'text_link') res.push(`](${cache[y].url})`);
      cache.splice(y, 1);
    }
  }
  return res
    .filter(Boolean)
    .join('');
}