server.js

const request = require('request')
// const compression = require('compression')
const cors = require('cors')
const express = require('express')
const bodyParser = require('body-parser')
const app = express()
const http = require('http').Server(app)
const io = require('socket.io')(http)

app.use(express.static('dist', { index: 'demo.html', maxage: '4h' }))
app.use(bodyParser.json())

// handle admin Telegram messages
app.post('/hook', function (req, res) {
  try {
    const message = req.body.message || req.body.channel_post
    const chatId = message.chat.id
    const name = message.chat.first_name || message.chat.title || 'admin'
    const text = message.text || ''
    const reply = message.reply_to_message

    if (text.startsWith('/start')) {
      console.log('/start chatId ' + chatId)
      sendTelegramMessage(chatId,
        '*Welcome to Intergram* \n' +
        'Your unique chat id is `' + chatId + '`\n' +
        'Use it to link between the embedded chat and this telegram chat',
        'Markdown')
    } else if (reply) {
      let replyText = reply.text || ''
      let userId = replyText.split(':')[0]
      io.emit(chatId + '-' + userId, { name, text, from: 'admin' })
    } else if (text) {
      io.emit(chatId, { name, text, from: 'admin' })
    }
  } catch (e) {
    console.error('hook error', e, req.body)
  }
  res.statusCode = 200
  res.end()
})

// handle chat visitors websocket messages
io.on('connection', function (client) {
  client.on('register', function (registerMsg) {
    let userId = registerMsg.userId
    let chatId = registerMsg.chatId
    let messageReceived = false
    console.log('useId ' + userId + ' connected to chatId ' + chatId)

    client.on('message', function (msg) {
      messageReceived = true
      io.emit(chatId + '-' + userId, msg)
      let visitorName = msg.visitorName ? '[' + msg.visitorName + ']: ' : ''
      sendTelegramMessage(chatId, '*' + userId + '*:' + visitorName + ' ' + msg.text.trim(), 'Markdown')
    })

    client.on('disconnect', function () {
      if (messageReceived) {
        sendTelegramMessage(chatId, userId + ' has left')
      }
    })
  })
})

function sendTelegramMessage (chatId, text, parseMode) {
  request
    .post('https://api.telegram.org/bot' + process.env.TELEGRAM_TOKEN + '/sendMessage')
    .form({
      'chat_id': chatId,
      'text': text,
      'parse_mode': parseMode
    })
}

app.post('/usage-start', cors(), function (req, res) {
  console.log('usage from', req.query.host)
  res.statusCode = 200
  res.end()
})

// left here until the cache expires
app.post('/usage-end', cors(), function (req, res) {
  console.log('disconnected: ', req.query.host)
  res.statusCode = 200
  res.end()
})

http.listen(process.env.PORT || 3000, function () {
  console.log('listening on port:' + (process.env.PORT || 3000))
})

app.get('/.well-known/acme-challenge/:content', (req, res) => {
  res.send(process.env.CERTBOT_RESPONSE)
})

app.get('/fakeDE', (req, res) => {
  let faker = require('faker/locale/de')
  res.send(faker.name.findName())
})

app.get('/fakeEN', (req, res) => {
  let faker = require('faker/locale/en')
  res.send(faker.name.findName())
})