utils.js

const {readFile} = require('fs/promises');
const Prism = require('prismjs');
const loadLanguages = require('prismjs/components/');
loadLanguages(['ts', 'swift', 'php', 'java', 'kotlin'])

const newFileName = () => {
  const d = new Date();
  const adjustedISO = new Date(d.getTime() - d.getTimezoneOffset() * 60 * 1000)
    .toISOString()
    .substr(0, 19)
    .replace('T', ' ');
  return `code2pdf_${adjustedISO}.pdf`;
};

const extractExtension = (path) => {
  const fileExtMatch = path.match(/\.([^.]+)$/);
  if (!fileExtMatch) return;
  return fileExtMatch[1];
};

const validExtensions = ['js', 'c', 'cpp', 'cs', 'css', 'html', 'xml', 'svg', 'ts', 'swift', 'java', 'kt', 'php'];

const getLanguage = (path) => {
  const extension = extractExtension(path);
  let language = 'none';
  switch (extension) {
    case 'ts':
      language = 'typescript';
      break;
    case 'js':
      language = 'javascript';
      break;
    case 'c':
    case 'cpp':
    case 'cs':
      language = 'clike';
      break;
    case 'swift':
      language = 'swift';
      break;
    case 'css':
      language = 'css';
      break;
    case 'html':
    case 'xml':
    case 'svg':
      language = 'markup';
    case 'php':
      language = 'php';
    case 'kt':
      launguage = 'kotlin';
    case 'java':
      language = 'java'
  }
  return language;
};

const makeHtml = async (path) => {
  const lang = getLanguage(path);
  const code = await readFile(path, 'utf8');
  // Static generation of line numbers
  // https://stackoverflow.com/a/59577306/1615721
  // https://github.com/PrismJS/prism/blob/master/plugins/line-numbers/prism-line-numbers.js#L109
  const NEW_LINE_EXP = /\n(?!$)/g;
  let lineNumbersWrapper;

  Prism.hooks.add('after-tokenize', function (env) {
    const match = env.code.match(NEW_LINE_EXP);
    const linesNum = match ? match.length + 1 : 1;
    const lines = new Array(linesNum + 1).join('<span></span>');
    lineNumbersWrapper = `<span aria-hidden="true" class="line-numbers-rows">${lines}</span>`;
  });

  let formatted = Prism.highlight(code, Prism.languages[lang], lang);
  if (lineNumbersWrapper) formatted += lineNumbersWrapper;

  return `<h2>${path}</h2><pre class='line-numbers language-${lang}'><code class='language-${lang}'>${formatted}</code></pre><hr />`;
};

exports.extractExtension = extractExtension;
exports.validExtensions = validExtensions;
exports.newFileName = newFileName;
exports.makeHtml = makeHtml;