unbundle/src/processFile.js

import {dirname, basename} from 'path'
import {readFile} from 'fs'
import {transform} from 'babel-core'
import {promisify} from 'bluebird'
import {write} from './write'
import mkdirp from 'mkdirp'
import {parse} from './importResolve'

const babelOptions = {
  babelrc: false,
  ignore: null,
  sourceMaps: true
}

const babelPlugins = [
  'syntax-async-generators',
  'syntax-class-properties',
  'syntax-decorators',
  'syntax-do-expressions',
  'syntax-export-extensions',
  'syntax-function-bind',
  'syntax-function-sent',
  'syntax-object-rest-spread'
]

const babelPresets = [
]

function babelrc (options = {}, plugins = [], presets = []) {
  const result = Object.assign({}, babelOptions, options)
  result.plugins = babelPlugins.concat(plugins)
  result.presets = babelPresets.concat(presets)
  return result
}

const importResolveOptions = {}

const stages = [
  {
    // Inline NODE_ENV ("development"/"production")
    // Must run before minify-dead-code-elimination
    plugins: ['transform-node-env-inline'],
    // {plugins: ['transform-inline-environment-variables']},

    // Parse and transform JSX/Flow
    presets: ['react']
  },

  // Get rid of require() calls that are not used in the current prod/dev environment
  {plugins: ['minify-dead-code-elimination']},

  // Transform CommonJS to ES2015 modules
  {plugins: ['transform-commonjs-es2015-modules']},

  // Trace all import sources
  {plugins: [['transform-import-resolve', importResolveOptions]]},

  // Transform ES2015 modules to SystemJS for client-side asynchronous loading
  {plugins: ['transform-es2015-modules-systemjs']},

  // Transform to minified ES5 code
  {presets: ['latest', 'stage-0', 'babili']}
]

export async function processFile (file, output, destination) {
  importResolveOptions.parse = parse(file, output, destination)

  let code = await promisify(readFile)(file, 'utf8')
  let map = null

  for (const {plugins, presets} of stages) {
    ({code, map} = transform(code, babelrc({
      filename: file,
      inputSourceMap: map
    }, plugins, presets)))
  }

  await promisify(mkdirp)(dirname(output))
  await Promise.all([
    write(code + '\n//# sourceMappingURL=' + basename(output) + '.map', output),
    write(JSON.stringify(map), output + '.map')
  ])
}