index.js

'use strict'
const url = require('url')
const qs = require('querystring')
const EventEmitter = require('events').EventEmitter
const request = require('request')
const crypto = require('crypto')

class Bot extends EventEmitter {
  constructor (opts) {
    super()

    opts = opts || {}
    if (!opts.token) {
      throw new Error('Missing page token. See FB documentation for details: https://developers.facebook.com/docs/messenger-platform/quickstart')
    }
    this.token = opts.token
    this.app_secret = opts.app_secret || false
    this.verify_token = opts.verify || false
  }

  getProfile (id, cb) {
    if (!cb) cb = Function.prototype

    request({
      method: 'GET',
      uri: `https://graph.facebook.com/v2.6/${id}`,
      qs: {
        fields: 'first_name,last_name,profile_pic',
        access_token: this.token
      },
      json: true
    }, (err, res, body) => {
      if (err) return cb(err)
      if (body.error) return cb(body.error)

      cb(null, body)
    })
  }

  sendMessage (recipient, payload, cb) {
    if (!cb) cb = Function.prototype

    request({
      method: 'POST',
      uri: 'https://graph.facebook.com/v2.6/me/messages',
      qs: {
        access_token: this.token
      },
      json: {
        recipient: { id: recipient },
        message: payload
      }
    }, (err, res, body) => {
      if (err) return cb(err)
      if (body.error) return cb(body.error)

      cb(null, body)
    })
  }

  middleware () {
    return (req, res) => {
      // we always write 200, otherwise facebook will keep retrying the request
      res.writeHead(200, { 'Content-Type': 'application/json' })
      if (req.url === '/_status') return res.end(JSON.stringify({status: 'ok'}))
      if (this.verify_token && req.method === 'GET') return this._verify(req, res)
      if (req.method !== 'POST') return res.end()

      let body = ''

      req.on('data', (chunk) => {
        body += chunk
      })

      req.on('end', () => {
        // check message integrity
        if (this.app_secret) {
          let hmac = crypto.createHmac('sha1', this.app_secret)
          hmac.update(body)

          if (req.headers['x-hub-signature'] !== `sha1=${hmac.digest('hex')}`) {
            this.emit('error', new Error('Message integrity check failed'))
            return res.end(JSON.stringify({status: 'not ok', error: 'Message integrity check failed'}))
          }
        }

        let parsed = JSON.parse(body)
        this._handleMessage(parsed)

        res.end(JSON.stringify({status: 'ok'}))
      })
    }
  }

  _handleMessage (json) {
    let entries = json.entry

    entries.forEach((entry) => {
      let events = entry.messaging

      events.forEach((event) => {
        // handle inbound messages
        if (event.message) {
          this._handleEvent('message', event)
        }

        // handle postbacks
        if (event.postback) {
          this._handleEvent('postback', event)
        }

        // handle message delivered
        if (event.delivery) {
          this._handleEvent('delivery', event)
        }

        // handle authentication
        if (event.optin) {
          this._handleEvent('authentication', event)
        }
      })
    })
  }

  _verify (req, res) {
    let query = qs.parse(url.parse(req.url).query)

    if (query['hub.verify_token'] === this.verify_token) {
      return res.end(query['hub.challenge'])
    }

    return res.end('Error, wrong validation token')
  }

  _handleEvent (type, event) {
    this.emit(type, event, this.sendMessage.bind(this, event.sender.id))
  }
}

module.exports = Bot