A stateless 'function' endpoint that responds to HTTP events sent by Telegram Clients that are chatting to SongwhipBot directly or have SongwhipBot added to a group.

Tech overview

• Uses Telegram WebHooks API so that the bot can be hosted in a serverless/Lambda environment, woken-up by inbound requests as opposed to polling for changes.
• There's a risk this could be an expensive service as it listens to every message send in a group for a music link. We'll monitor it.
• We opt-out of replying via the original inbound http response (via webhookReply: false) so that we can resolve the request straight away and send a string of follow-up messages after. This makes things simpler when sending more than one message response.
• The vercel.json defines production env vars, when we deploy to staging with yarn deploy:staging we override select env vars so that the @SongwhipDevBot token is used instead of @SongwhipBot and the staging endpoint songwhip-telegram.wilsonpage.now.sh is used.
• Some bot configuration (eg. the command list or enabling 'inline' command) must be done from the Telegram app via the @BotFather bot.
• We're using now secret from the CLi to store the Telegram bot token, which is used in now.json via the magic @songwhip-telegram-bot-token placeholder.

Establishing the webhook endpoint with Telegram

1. Set the SONGWHIP_TELEGRAM_URL to the URL of the deployment
2. Deploy
3. Visit /set-webhook on the deployment to setup the connection between Telegram and the deployment endpoint.