const fs = require('fs');

const getModules = projectDir =>
  fs
    .readdirSync(`${projectDir}/node_modules`)
    .map(ns => {
      if (ns[0] === '@') {
        return fs
          .readdirSync(`${projectDir}/node_modules/${ns}`)
          .map(name => `${projectDir}/node_modules/${ns}/${name}/package.json`);
      }

      return `${projectDir}/node_modules/${ns}/package.json`;
    })
    .reduce(
      (acc, path) => (Array.isArray(path) ? [...acc, ...path] : [...acc, path]),
      [],
    )
    .filter(path => fs.existsSync(path))
    .map(path => ({
      pkg: JSON.parse(fs.readFileSync(path, { encoding: 'utf8' })),
      path,
    }));

const fixPackages = projectDir => {
  const modules = getModules(projectDir);
  let count = 0;

  modules.forEach(({ path, pkg }) => {
    if (pkg.module && pkg.main && !pkg.browser) {
      pkg.browser = pkg.main;
      fs.writeFileSync(path, JSON.stringify(pkg, '', '  '), {
        encoding: 'utf8',
      });
      count++;
    }
  });

  console.log(`modified ${count} packages to prefer 'main' over 'module'`);
};

// the directory that holds your 'package.json'
fixPackages('./');