const path = require('path');

module.exports = ({ config, mode }) => {
  // Transpile Gatsby module because Gatsby includes un-transpiled ES6 code.
  config.module.rules[0].exclude = [/node_modules\/(?!(gatsby)\/)/];

  // use installed babel-loader which is v8.0-beta (which is meant to work with @babel/core@7)
  config.module.rules[0].use[0].loader = require.resolve('babel-loader');

  // use @babel/preset-react for JSX and env (instead of staged presets)
  config.module.rules[0].use[0].options.presets = [
    require.resolve('@babel/preset-react'),
    require.resolve('@babel/preset-env'),
  ];

  config.module.rules[0].use[0].options.plugins = [
    // use @babel/plugin-proposal-class-properties for class arrow functions
    require.resolve('@babel/plugin-proposal-class-properties'),
    // use babel-plugin-remove-graphql-queries to remove static queries from components when rendering in storybook
    require.resolve('babel-plugin-remove-graphql-queries'),
  ];

  // Prefer Gatsby ES6 entrypoint (module) over commonjs (main) entrypoint
  config.resolve.mainFields = ['browser', 'module', 'main'];

  config.module.rules.push({
    test: /\.scss$/,
    use: ['style-loader', 'css-loader', 'sass-loader'],
    include: path.resolve(__dirname, '../'),
  });

  config.module.rules = config.module.rules.map(rule => {
    if (!rule.test.test('.svg')) {
      return rule;
    }

    const newRule = rule;
    // Changes existing default rule to not handle SVG files
    newRule.test = /\.(ico|jpg|jpeg|png|gif|eot|otf|webp|ttf|woff|woff2)(\?.*)?$/;
    return newRule;
  });

  // Adds new SVG loader
  config.module.rules.push({
    test: /\.svg$/,
    use: ['@svgr/webpack', 'url-loader'],
  });

  config.module.rules.push({
    test: /\.stories\.jsx?$/,
    loaders: [require.resolve('@storybook/addon-storysource/loader')],
    enforce: 'pre',
  });

  return config;
};