const mdx = require('@mdx-js/mdx')
const matter = require('gray-matter')
const stringifyObject = require('stringify-object')
const normalizeNewline = require('normalize-newline')

const EXREG = /export\sdefault\s\(/g
const MODREG = /^(import|export)\s/
const SLIDEREG = /\n---\n/

module.exports = async function (src) {
  const callback = this.async()

  const { data, content } = matter(src)

  const inlineModules = []
  const slides = normalizeNewline(content)
    .split(SLIDEREG)
    .map(str => mdx.sync(str))
    .map(str => str.trim())
    .map(str => str.replace(EXREG, '('))
    .map(str => {
      const lines = str.split('\n')
      inlineModules.push(
        ...lines.filter(str => MODREG.test(str))
      )
      return lines.filter(str => !MODREG.test(str))
        .filter(Boolean)
        .join('\n')
    })

  const {
    modules = []
  } = data

  const code = `import React from 'react'
import { MDXTag } from '@mdx-js/tag'
${modules.join('\n')}
${inlineModules.join('\n')}

export const meta = ${stringifyObject(data)}

export default [
  ${slides.join(',\n\n')}
]`

  return callback(null, code)
}