introduce telegram-chat

Druvis from Mikrotik produced a video "MikroTik Telegram bot - Chat with
your Router?". He shows his script to chat with a Router via Telegram
bot to send it commands: https://youtu.be/KLX6j3sLRIE

This script is kind of limited and has several issues... 🥴

Let's make it robust, usable, multi-device capable and just fun! 😁

(Sadly Mikrotik has a policy to not allow links in Youtube comments.
Thus my comment with several hints was removed immediately. If anybody
is in contact with Druvis... Please tell him about this script!)

doc/mod/notification-telegram.md

@@ -66,6 +66,7 @@ methods:
 See also
 --------
 
+* [Chat with your router and send commands via Telegram bot](../telegram-chat.md)
 * [Send notifications via e-mail](notification-email.md)
 * [Send notifications via Matrix](notification-matrix.md)
 

doc/telegram-chat.md

@@ -0,0 +1,89 @@
+Chat with your router and send commands via Telegram bot
+========================================================
+
+[⬅️ Go back to main README](../README.md)
+
+> ℹ️ **Info**: This script can not be used on its own but requires the base
+> installation. See [main README](../README.md) for details.
+
+Description
+-----------
+
+This script makes your device poll a Telegram bot for new messages. With
+these messages you can send commands to your device and make it run them.
+The resulting output is send back to you.
+
+Requirements and installation
+-----------------------------
+
+Just install the script and the module for notifications via Telegram:
+
+    $ScriptInstallUpdate telegram-chat,mod/notification-telegram;
+
+Then create a schedule that runs the script periodically:
+
+    /system/scheduler/add start-time=startup interval=30s name=telegram-chat on-event="/system/script/run telegram-chat;";
+
+> ⚠️ **Warning**: Make sure to keep the interval in sync when installing
+> on several devices. Differing polling intervals will result in missed
+> messages.
+
+Configuration
+-------------
+
+Make sure to configure
+[notifications via telegram](mod/notification-telegram.md) first. The
+additional configuration goes to `global-config-overlay`, these are the
+parameters:
+
+* `TelegramChatIdsTrusted`: an array with trusted chat ids or user names
+* `TelegramChatGroups`: define the groups a device should belong to
+
+Usage and invocation
+--------------------
+
+This script is capable of chatting with multiple devices. By default a
+device is passive and not acting on messages. To activate it send a message
+containing `! identity` (exclamation mark, optional space and system's
+identity). To query all dynamic ip addresses form a device named "*MikroTik*"
+send `! MikroTik`, followed by `/ip/address/print where dynamic;`.
+
+![chat to specific device](telegram-chat.d/01-chat-specific.avif)
+
+Devices can be grouped to chat with them simultaneously. The default group
+"*all*" can be activated by sending `! @all`, which will make all devices
+act on your commands.
+
+![chat to all devices](telegram-chat.d/02-chat-all.avif)
+
+Send a single exclamation mark or non-existent identity to make all
+devices passive again.
+
+Known limitations
+-----------------
+
+### Do not use numeric ids!
+
+Numeric ids are valid within a session only. Usually you can use something
+like this to print all ip addresses and remove the first one:
+
+    /ip/address/print;
+    /ip/address/remove 0;
+
+This will fail when sent in separate messages. Instead you should use basic
+scripting capabilities. Try to print what you want to act on...
+
+    /ip/address/print where interface=eth;
+
+... verify and finally remove it.
+
+    /ip/address/remove [ find where interface=eth ];
+
+See also
+--------
+
+* [Send notifications via Telegram](mod/notification-telegram.md)
+
+---
+[⬅️ Go back to main README](../README.md)  
+[⬆️ Go back to top](#top)