module.exports = options => {
  const aliases = Object.keys(options);
  const re = new RegExp(`^(${aliases.map(x => escapeRegExp(x)).join('|')})$`);

  return {
    name: 'alias',
    setup(build) {
      // we do not register 'file' namespace here, because the root file won't be processed
      // https://github.com/evanw/esbuild/issues/791
      build.onResolve({ filter: re }, args => ({
        path: options[args.path],
      }));
    },
  };
};

function escapeRegExp(string) {
  // $& means the whole matched string
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}