ahbeng/NUSMods

const pkgJson = require('./package.json');

module.exports = (api) => {
  api.cache.using(() => process.env.NODE_ENV);

  const IS_PROD = api.env('production');
  const IS_DEV = api.env('development');
  const IS_TEST = api.env('test');

  // Presets are evaluated last-to-first, while plugins are evaluated first-to-last
  // This means the TS preset must come last to enable language transformation first
  const presets = [
    [
      '@babel/preset-env',
      {
        targets: IS_TEST ? { node: true } : { browsers: pkgJson.browserslist },
        modules: IS_TEST ? 'commonjs' : false,
        useBuiltIns: 'usage',
        corejs: pkgJson.dependencies['core-js'],
        // Exclude transforms that make all code slower
        // See https://github.com/facebook/create-react-app/pull/5278
        exclude: ['transform-typeof-symbol'],
      },
    ],
    [
      '@babel/preset-react',
      {
        development: !IS_PROD,
        // Enable JSX transform
        // TODO: Remove in Babel 8, when this will be the default option
        // See: https://reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html#manual-babel-setup
        runtime: 'automatic',
      },
    ],
    [
      '@babel/preset-typescript',
      {
        allowDeclareFields: true,
      },
    ],
  ];

  const plugins = ['babel-plugin-lodash'];

  const assumptions = {
    // Assumes document.all doesn't exist to reduce the generated code size
    noDocumentAll: true,

    // Deviate from spec, but Object.defineProperty is expensive
    // See https://github.com/facebook/create-react-app/issues/4263
    // Using assignment also reduces the generated code size
    privateFieldsAsProperties: true,
    setPublicClassFields: true,
  };

  if (IS_DEV) {
    plugins.push('react-refresh/babel');
  }

  if (IS_PROD) {
    // React Optimize plugins
    plugins.push(
      '@babel/plugin-transform-react-inline-elements',
      '@babel/plugin-transform-react-constant-elements',
      'babel-plugin-transform-react-remove-prop-types',
      'babel-plugin-transform-react-class-to-function',
    );
  }

  if (IS_TEST) {
    plugins.push('babel-plugin-dynamic-import-node');
  }

  return {
    assumptions,
    sourceType: 'unambiguous',
    presets,
    plugins,
  };
};