index.js

const defined = require('defined')
const postcss = require('postcss')
const extend = require('xtend')
const resolve = require('resolve')
const postcssrc = require('postcss-load-config')

module.exports = transform

function transform (filename, source, options, done) {
  options = defined(options, {})

  const basedir = options.basedir

  const plugins = defined(options.plugins, [])
    .map(plugin => {
      if (typeof plugin === 'string') {
        plugin = [plugin]
      }

      return {
        path: resolve.sync(plugin[0], { basedir }),
        options: plugin[1]
      }
    })
    .map(plugin => require(plugin.path)(plugin.options))

  const ctx = extend({
    sourcemap: true,
    from: filename,
    messages: {
      browser: true,
      console: false
    }
  }, options)

  delete ctx.plugins

  postcssrc(ctx, basedir).then(compile, function () {
    return compile({ options: ctx })
  }).then(function (result) {
    done(null, result)
  }, done)

  function compile (config) {
    return postcss(plugins.concat(config.plugins).filter(Boolean))
      .process(source, config.options)
      .then(function (result) {
        // Collect imported files for watchify
        const files = [filename]
        result.messages.forEach(function (msg) {
          if (msg.type === 'dependency') {
            files.push(msg.file)
          }
        })

        return {
          css: result.css,
          files: files
        }
      })
  }
}