feat: add Telegram watchdog as backup notification channel

- New src/telegramBot.js: separate process for health checks + Telegram notifications
- Updated src/whatsappApi.js notifyAdmin(): falls back to Telegram when WhatsApp API is down
- Updated .env.example with TELEGRAM_* configuration variables
- Design doc and implementation plan

src/telegramBot.js

@@ -0,0 +1,101 @@
+require('dotenv').config()
+const express = require('express')
+const axios = require('axios')
+
+const BOT_TOKEN = process.env.TELEGRAM_BOT_TOKEN
+const ADMIN_CHAT_ID = process.env.TELEGRAM_ADMIN_CHAT_ID
+const PORT = process.env.TELEGRAM_BOT_PORT || 3004
+const DIENST_BOT_HEALTH = process.env.DIENST_BOT_HEALTH_URL || 'http://localhost:3002/health'
+const WWEBJS_SESSION = process.env.WWEBJS_API_SESSION_URL || 'http://192.168.5.252:3001/session/status/EdGpt'
+const CHECK_INTERVAL = parseInt(process.env.HEALTH_CHECK_INTERVAL_MS || '300000', 10)
+
+const app = express()
+app.use(express.json())
+
+let dienstBotOk = true
+let wwebjsOk = true
+
+function sendTelegram(text) {
+  return axios.post(`https://api.telegram.org/bot${BOT_TOKEN}/sendMessage`, {
+    chat_id: ADMIN_CHAT_ID,
+    text,
+    parse_mode: 'Markdown'
+  }, { timeout: 10000 })
+}
+
+async function startupNotification() {
+  try {
+    await sendTelegram('✅ Telegram watchdog online — gezondheidschecks actief')
+    console.log('Startup notification sent')
+  } catch (err) {
+    console.error('Failed to send startup notification:', err.message)
+  }
+}
+
+async function checkHealth() {
+  let currentDienstBotOk = true
+  let currentWwebjsOk = true
+
+  try {
+    await axios.get(DIENST_BOT_HEALTH, { timeout: 5000 })
+  } catch {
+    currentDienstBotOk = false
+  }
+
+  try {
+    const res = await axios.get(WWEBJS_SESSION, { timeout: 5000 })
+    currentWwebjsOk = res.data?.state === 'CONNECTED'
+  } catch {
+    currentWwebjsOk = false
+  }
+
+  if (dienstBotOk !== currentDienstBotOk) {
+    const icon = currentDienstBotOk ? '✅' : '❌'
+    const status = currentDienstBotOk ? 'weer online' : 'niet bereikbaar'
+    try {
+      await sendTelegram(`${icon} dienst-bot ${status}`)
+    } catch (err) {
+      console.error('Failed to send dienst-bot status:', err.message)
+    }
+    dienstBotOk = currentDienstBotOk
+  }
+
+  if (wwebjsOk !== currentWwebjsOk) {
+    const icon = currentWwebjsOk ? '✅' : '❌'
+    const status = currentWwebjsOk ? 'weer online' : 'niet bereikbaar'
+    try {
+      await sendTelegram(`${icon} wwebjs-api ${status}`)
+    } catch (err) {
+      console.error('Failed to send wwebjs-api status:', err.message)
+    }
+    wwebjsOk = currentWwebjsOk
+  }
+
+  console.log(`Health check: dienst-bot=${currentDienstBotOk ? 'UP' : 'DOWN'}, wwebjs-api=${currentWwebjsOk ? 'UP' : 'DOWN'}`)
+}
+
+app.post('/notify', async (req, res) => {
+  const { text } = req.body
+  if (!text) {
+    return res.status(400).json({ success: false, error: 'missing text' })
+  }
+  try {
+    await sendTelegram(`⚠️ ${text}`)
+    res.json({ success: true })
+  } catch (err) {
+    console.error('Failed to forward notification:', err.message)
+    res.status(500).json({ success: false, error: err.message })
+  }
+})
+
+app.get('/health', (req, res) => {
+  res.json({ status: 'ok', services: { dienstBot: dienstBotOk, wwebjsApi: wwebjsOk } })
+})
+
+startupNotification()
+setInterval(checkHealth, CHECK_INTERVAL)
+checkHealth()
+
+app.listen(PORT, () => {
+  console.log(`telegram-bot listening on port ${PORT}`)
+})

src/whatsappApi.js

@@ -73,7 +73,15 @@ async function notifyAdmin(errorText) {
   try {
     await sendTextMessage(adminNumber, `[dienst-bot fout] ${errorText}`)
   } catch (err) {
-    console.error('Failed to notify admin:', err.message)
+    console.error('WhatsApp admin notification failed, falling back to Telegram:', err.message)
+    try {
+      const telegramUrl = process.env.TELEGRAM_BOT_URL
+      if (telegramUrl) {
+        await axios.post(`${telegramUrl}/notify`, { text: errorText }, { timeout: 5000 })
+      }
+    } catch (telegramErr) {
+      console.error('Telegram notification also failed:', telegramErr.message)
+    }
   }
 }