index.js

require('dotenv').config()

const { createEventAdapter } = require('@slack/events-api')
const { WebClient } = require('@slack/web-api')
const assert = require('assert')
const axios = require('axios')
const uuid = require('uuid/v4')

const port = process.env.PORT || 3000
const token = process.env.SLACK_TOKEN
const PTTAI_GATEWAY_URL = process.env.PTTAI_GATEWAY_URL
const PTTAI_TOKEN = process.env.PTTAI_TOKEN
const SLACK_SIGNING_SECRET = process.env.SLACK_SIGNING_SECRET

assert.ok(port, 'PORT is undefined')
assert.ok(token, 'SLACK_TOKEN is undefined')
assert.ok(PTTAI_GATEWAY_URL, 'PTTAI_GATEWAY is undefined')
assert.ok(PTTAI_TOKEN, 'PTTAI_TOKEN is undefiend')
assert.ok(SLACK_SIGNING_SECRET, 'SLACK_SIGNING_SECRET is undefined')

const userMentions = /<@([^<]+)>/g
const mentionedUserID = /<@([^<]+)>/

async function main () {
  const web = new WebClient(token)

  let channels = await loadChannels(web)
  console.log(channels)
  let users = await loadUsers(web)

  const slackEvents = createEventAdapter(SLACK_SIGNING_SECRET)
  slackEvents.on('message', async (event) => {
    console.log(event)
    let text = event.text
    if (users[event.user]) {
      // replace mentioned user ID to user name
      if (text.match(userMentions)) {
        for (let mention of text.match(userMentions)) {
          let userID = mention.match(mentionedUserID)[1]
          if (userID) {
            text = text.replace(userID, users[userID])
          }
        }
      }

      console.log(`Received a message event: user ${users[event.user]} in channel ${channels[event.channel]} says ${text} with ${event.files ? event.files.length : 0} files`)
      let fileURLs = event.files ? event.files.map(f => f.url_private) : []

      await post(channels[event.channel], `<${users[event.user]}>: ${text} ${fileURLs.join(' ')}`)
    }
  })

  slackEvents.on('error', (err) => {
    if (err instanceof TypeError) return

    console.error(err)
  })

  slackEvents.start(port).then(() => {
    console.log(`server listening on port ${port}`)
  })
}

async function loadUsers (web) {
  let t = {}
  let res = await web.users.list()
  res.members.forEach(x => { t[x.id] = x.name })

  return t
}

async function loadChannels (web) {
  let t = {}
  let res = await web.channels.list()
  res.channels.forEach(x => { t[x.id] = x.name })

  return t
}

async function post (topic, text) {
  return axios.request({ url: `${PTTAI_GATEWAY_URL}/topics/${topic}`, data: { data: { id: uuid(), message: { type: 'text', value: text } } }, method: 'POST', params: { token: PTTAI_TOKEN } })
}

main()