purescript psc 0.9 output webpack loader that allows tree shaking

commonjs-to-es6-modules.js

"use strict"

/*
 * Webpack 2 loader that can take CommonJS output by psc 0.9.1 and convert 
 * it into tree shakable ES6 modules. No transpiling required. 
 */
const fs = require('fs')

const commonJsRequire = /var ([$\w]+) = require\("(.*)"\)/g
const moduleExports = /module\.exports = \{(\n(    ([$\w]+): ([$\w]+)(, )?\n)*)?\};/m
const actualExports = /(    ([$\w]+): ([$\w]+)(, )?\n)/g


module.exports = function (content) {
  this.cacheable() 

  const funcs = [
    upconvertImports,
    upconvertExports,
    upconvertFfiExports
  ]

  let out = funcs.reduce((prev, curr) => curr(prev), content)
  console.log(out)
  return out
}

function findMatches(regex, content, action) {
  let current;
  let updated = content.slice()

  while ((current = regex.exec(content)) !== null) {
    updated = action(updated, current)
  }
  return updated
}

function upconvertImports (content) {
  function action (content, currentImport) {
    let [commonJsImport, identifier, file] = currentImport
    return content.replace(commonJsImport, `import * as ${identifier} from "${file}"`)
  }
  return findMatches(commonJsRequire, content, action)
}

function upconvertExports (content) {
  function action (noop, currentExport) {
    let [_, __, internalName, externalName] = currentExport

    if (internalName === externalName) {
      content = content.replace(
        `var ${internalName} =`,
        `export var ${internalName} =`)
    }
    else {
      content += `export var ${externalName} = ${internalName};`
    }

    return content.replace(moduleExports, '')
  }

  let moduleExporting = moduleExports.exec(content)

  if (moduleExporting) {
    let [exportsBlob, _] = moduleExporting

    return findMatches(actualExports, exportsBlob, action)
  }

  return content
}

function upconvertFfiExports (content) {
  return content.replace(/^exports\./gm, 'export var ')
}