const {text, json, createError} = require('micro')
const {get, post, withNamespace} = require('microrouter')
const FB = require('fb')

FB.setAccessToken(process.env.FB_ACCESS_TOKEN)

const fbParser = require('claudia-bot-builder/lib/facebook/parse')
const fbValidate = require('claudia-bot-builder/lib/facebook/validate-integrity')

const {run} = require('./intents')

/**
 * In-Memory cache for FB graph results
 */
const recipients = []

/**
 * GET webhook
 *
 * Gets executed when you add the Webhook URL to the Facebook and it tries
 * to validate it.
 */
const verifyToken = req => {
  if (req.query['hub.verify_token'] === process.env.FB_VERIFY_TOKEN) {
    return req.query['hub.challenge']
  }
  console.info(
    `Your Facebook Access Token (that Facebook will echo back to you as part of callback URL verification): ${
      process.env.FB_VERIFY_TOKEN
    }`
  )
  return 'INVALID TOKEN'
}

/**
 * Validate and convert request to a common message format
 */
const fbMessage = async req => {
  req.env = {facebookAppSecret: process.env.FB_APP_SECRET}
  req.rawBody = await text(req)
  const data = await json(req)
  const [[message]] = data.entry.map(entry =>
    entry.messaging.map(message => fbParser(message))
  )

  const isValid = fbValidate(req) && message.type === 'facebook'

  return isValid ? message : false
}

/**
 * POST webhook
 *
 * Gets executed on any message to the Bot.
 */
const respond = async (req, res) => {
  const message = await fbMessage(req)
  if (message) {
    const recipient =
      recipients[message.sender] || (await FB.api(message.sender))

    // Cache recipients
    recipients[message.sender] = recipient

    try {
      await run(message, recipient)
    } catch (err) {
      console.error(err)
      res.end(err.message)
    }

    res.end()
  } else {
    throw createError(400, 'Invalid message signature.')
  }
}

const fbApi = withNamespace('/api/v1/facebook')
module.exports = fbApi(get('/', verifyToken), post('/', respond))