#!/usr/bin/env node
import { chain } from 'lodash'
import { join } from 'path'
import fs from 'fs'
import Promise from 'bluebird'

Promise.promisifyAll(fs)

const CWD = process.cwd()
const PACKAGE_PATH = join(CWD, 'package.json')

fs.existsAsync = function(path){
  return fs.openAsync(path, "r").then(function(stats){
    return true
  }).catch(function(stats){
    return false
  })
}

export function checkExists (file) {
  return fs.existsAsync(file).then(exists => {
    if (!exists) throw new Error(`package.json does not exist in dir ${CWD}`)
    return exists
  })
}

export function readPackageJson (file) {
  return fs.readFileAsync(PACKAGE_PATH, 'utf8').then(file => {
    try {
      return JSON.parse(file)
    } catch (e) {
      throw new Error('package.json contains invalid JSON')
    }
  })
}

export function writePackageJson (file, content) {
  content = JSON.stringify(content, null, 2)
  return fs.writeFileAsync(PACKAGE_PATH, content, 'utf8')
}

export function getBabelPresets (packageJson) {
  let deps = packageJson.devDependencies
  let pat = /^babel-preset-/
  return chain(deps)
    .keys()
    .filter(dep => dep.match(pat))
    .map(dep => dep.replace(pat, ''))
    .value()
}

Promise.resolve()
  .then(() => checkExists(PACKAGE_PATH))
  .then(() => readPackageJson(PACKAGE_PATH))
  .then((packageJson) => {
    packageJson.babel = {}
    packageJson.babel.presets = getBabelPresets(packageJson)
    return packageJson
  })
  .then(packageJson => writePackageJson(PACKAGE_PATH, packageJson))