Babel macro to create HTML from Markdown

converter.js

function getConverter(showdown) {
  showdown.setFlavor('github');
  showdown.subParser('runExtension', (ext, source, options, globals) => {
    let text = source;
    if (ext.filter) {
      text = ext.filter(text, globals.converter, options, globals);
    }
    return text;
  });
  return new showdown.Converter({
    extensions: [
      () => [
        /*
         * Transform custom syntax
         * [[hello]]
         *
         * To:
         * <span class="box">hello</span>
         *
         */
        {
          type: 'lang',
          filter(source) {
            const pattern = /\[\[(.*?)\]\]/g;
            let text = source;
            text = text.replace(pattern, (wholeMatch, content) => (
              `<span class="box">${content}</span>`
            ));
            return text;
          },
        },
      ],
    ],
  });
}

exports.getConverter = getConverter;

richdown.macro.js

const fs = require('fs');
const path = require('path');
const { createMacro } = require('babel-plugin-macros');
const showdown = require('showdown');
const { getConverter } = require('./converter');

function richdown({ references, babel, state }) {
  references.default.forEach(referencePath => {
    if (babel.types.isTaggedTemplateExpression(referencePath.parent)) {
      const quasiPath = referencePath.parentPath.get('quasi');
      const valueString = quasiPath.parentPath.get('quasi').evaluate().value;
      const value = converter.makeHtml(valueString);
      const valueNode = babel.types.stringLiteral(value);
      quasiPath.parentPath.replaceWith(valueNode);
    } else if (babel.types.isCallExpression(referencePath.parent)) {
      const quasiPath = referencePath.parentPath.get('quasi');
      const filepath = referencePath.parent.arguments[0].value;
      const fullpath = path.resolve(path.dirname(state.filename), filepath)
      const valueString = fs.readFileSync(fullpath, 'utf8');
      const value = converter.makeHtml(valueString);
      const valueNode = babel.types.stringLiteral(value);
      quasiPath.parentPath.replaceWith(valueNode);
    }
  });
}

const converter = getConverter(showdown);

module.exports = createMacro(richdown);

usage.js

import richdown from './richdown.macro';

const htmlFromInline = richdown`
hello, **world**
`;

const htmlFromFile = richdown('hello.md');