# scrabble/platform/telegram — Telegram validator + bot

The Telegram platform side-service, split into **two binaries** that share the bot
token, so Telegram egress lives off the main host while game login does not depend on
it. See [`docs/ARCHITECTURE.md`](../../docs/ARCHITECTURE.md) §1/§3/§10/§12/§13.

- **`cmd/validator`** (home) — verifies Mini App `initData` and Login Widget data by
  HMAC (the bot token is the secret) and **never calls the Bot API**. It serves the
  validation gRPC API the gateway calls during Telegram auth, on the trusted internal
  network with no VPN. Because it needs no Telegram reachability, **game login stays up
  even when the bot or the bot-link is down**.
- **`cmd/bot`** (remote) — runs the Bot API long-poll (Mini App launch + `/start`
  deep-links) and `sendMessage`, the only component reaching the Telegram Bot API. It
  holds **no inbound port**: it dials the gateway over a reverse **mTLS bot-link** and
  executes the send commands the gateway pushes, so its egress can run on a host with
  native Telegram access (a VPN sidecar in the test contour, a separate host in prod).

Both hold the same token. One bot owns the exclusive `getUpdates` long-poll
(`TELEGRAM_OWNS_UPDATES`, exactly one per token, else Telegram returns 409); the
design leaves seams (a gateway bot registry, the `owns_updates` flag, per-command ids)
for running several bots later, not built yet.

## Validator

`ValidateInitData` validates `initData` against the token and returns only the
Telegram user identity (no per-bot service language, no supported-languages set);
`ValidateLoginWidget` verifies Telegram **Login Widget** web sign-in data — HMAC under
`SHA-256(bot_token)`, distinct from initData (`internal/loginwidget`) — for attaching a
Telegram identity to an account from a browser. Both map a rejection to gRPC
`InvalidArgument`.

## Bot

- **Send commands.** The gateway pushes `Notify` (out-of-app push: your_turn,
  game_over, nudge, match_found, and the invitation / friend_request notify sub-kinds),
  `SendToUser` and `SendToGameChannel` (operator broadcasts) down the bot-link. The bot
  renders the message in the command's `language` (the recipient's interface language;
  operator-chosen for broadcasts) with a Mini App launch button and sends it. It replies
  with an `Ack` per command (`delivered` mirrors the former connector semantics —
  false when the kind is not rendered out-of-app or the user never started the bot).
- **Bot chat.** `/start <payload>` (and the chat menu button) reply with a Mini App
  launch button; a deep-link payload routes the launch to a game / invitation / friend
  code. This is **self-contained** — the bot never calls back into the game, so `/start`
  onboarding works even when the game is down.
- **Moderated-chat gating.** When `TELEGRAM_CHAT_ID` names a channel's linked discussion
  group, the bot gates who may write there. The group **allows sending by default** (a
  human setting) and the bot only **restricts** — Telegram intersects the chat default with
  each user's permission, so a per-user grant cannot exceed a deny-by-default group, and the
  gate must mute the ineligible rather than grant the eligible. On a `chat_member` event the
  bot asks the gateway (`ResolveChatEligibility`) and **mutes** a member who is not registered
  or is admin-suspended or `chat_muted`, **un-mutes** an eligible one it had muted, and leaves
  an already-allowed eligible member untouched (it acts only when the state differs, so it is
  idempotent and skips its own change). When an operator blocks/unblocks an account, toggles
  its `chat_muted` role, or a user first registers, the gateway pushes a `ChatGate` command and
  the bot applies it — but only to a member currently in the chat (it probes one user with
  `getChatMember`, since bots cannot list members). The bot must be an **administrator** there
  with the **"Ban users"** right (the Bot API `can_restrict_members`), and it subscribes to
  `chat_member` updates, which Telegram delivers only to a chat admin.
- **Promo bot (optional).** When `TELEGRAM_PROMO_BOT_TOKEN` is set, the container also
  runs a **second, standalone** bot whose only job is to answer `/start` with a localized
  message and a button that opens the **main** bot's Mini App. The button is a **URL** to
  the main bot's direct link (`TELEGRAM_BOT_LINK`, the same link the UI uses) with
  `?startapp` — a `web_app` button would launch under the promo bot's identity (its token
  would sign the initData), which the main bot's validator rejects. It is fully
  self-contained: no bot-link, no gateway, no game.
- **Rate limiting.** Outbound sends are throttled (`TELEGRAM_SEND_RATE_PER_SECOND`,
  default 25) to respect the Bot API flood limits.

The send commands address a recipient by the identity `external_id` (as in the backend
`identities` table), so a future VK / MAX bot reuses them; only the validator's initData
parsing is Telegram-specific.

## gRPC contracts

- `pkg/proto/telegram/v1`, service `Telegram` — served by the **validator**
  (`ValidateInitData`, `ValidateLoginWidget`). Its `Notify` / `SendToUser` /
  `SendToGameChannel` request shapes are reused as bot-link command payloads; the
  gateway also implements `SendToUser` / `SendToGameChannel` as the backend's admin
  relay.
- `pkg/proto/botlink/v1`, service `BotLink` — the reverse bidi stream the **bot** dials
  on the gateway (`Hello` / `Command` / `Ack`), now also carrying a `ChatGateCommand` (set
  a user's chat write access) and a unary `ResolveChatEligibility` (the bot's join-time
  query) over the same mTLS channel. Generated Go is committed under `pkg`.

## Deep-link scheme

Shared verbatim with the UI (`ui/src/lib/deeplink.ts`). A Mini App start parameter is a
one-character kind prefix plus a value:

| Parameter | Destination |
| --- | --- |
| `g<game uuid>` | open that game |
| `i<invitation uuid>` | open that invitation |
| `f<6-digit code>` | redeem that friend code |
| empty / unknown | the lobby |

The bot turns a `/start <payload>` or a notification target into a launch-button URL
`<MiniAppURL>?startapp=<payload>`.

## Configuration

Shared:

| Env var | Default | Meaning |
| --- | --- | --- |
| `TELEGRAM_BOT_TOKEN` | — (required) | the bot's API token + initData HMAC secret |
| `TELEGRAM_LOG_LEVEL` | `info` | zap log level |
| `TELEGRAM_SERVICE_NAME` | per binary | OpenTelemetry `service.name` (validator: `scrabble-telegram-validator`, bot: `scrabble-telegram-bot`) |
| `TELEGRAM_OTEL_TRACES_EXPORTER` | `none` | `none`, `stdout` or `otlp` (gRPC; endpoint from `OTEL_EXPORTER_OTLP_*`) |
| `TELEGRAM_OTEL_METRICS_EXPORTER` | `none` | `none`, `stdout` or `otlp` |

Validator (`cmd/validator`):

| Env var | Default | Meaning |
| --- | --- | --- |
| `TELEGRAM_VALIDATOR_GRPC_ADDR` | `:9091` | validator gRPC listen address (the gateway dials it) |

Bot (`cmd/bot`):

| Env var | Default | Meaning |
| --- | --- | --- |
| `TELEGRAM_MINIAPP_URL` | — (required) | Mini App HTTPS origin (BotFather-registered) |
| `TELEGRAM_GATEWAY_ADDR` | — (required) | the gateway bot-link endpoint to dial |
| `TELEGRAM_BOTLINK_SERVER_NAME` | — (required) | the gateway certificate's expected SNI / CN |
| `TELEGRAM_BOTLINK_TLS_CERT` / `_KEY` / `_CA` | — (required) | the bot client cert, its key, and the CA that signs the gateway server cert |
| `TELEGRAM_GAME_CHANNEL_ID` | — | the bot's game channel chat id for `SendToGameChannel` |
| `TELEGRAM_CHAT_ID` | — | the moderated discussion chat id (a channel's linked group); empty disables chat gating |
| `TELEGRAM_PROMO_BOT_TOKEN` | — | the optional standalone promo bot's token; empty disables it |
| `TELEGRAM_BOT_USERNAME` | — | the main bot's @username without the @ (promo message); required when the promo bot runs |
| `TELEGRAM_BOT_LINK` | — | the main bot's Mini App link for the promo button (the UI's `VITE_TELEGRAM_LINK`); required when the promo bot runs |
| `TELEGRAM_OWNS_UPDATES` | `true` | run the exclusive `getUpdates` long-poll (one bot per token) |
| `TELEGRAM_SEND_RATE_PER_SECOND` | `25` | outbound Bot API send cap (0 disables) |
| `TELEGRAM_INSTANCE_ID` | hostname | bot identity reported to the gateway |
| `TELEGRAM_BOTLINK_RECONNECT_DELAY` | `2s` | pause before re-dialing after the stream ends |
| `TELEGRAM_API_BASE_URL` | `https://api.telegram.org` | Bot API host override (mock / self-hosted) |
| `TELEGRAM_TEST_ENV` | `false` | route to the Bot API **test environment** (`/bot<token>/test/METHOD`) |

## Build, test, run

```sh
go build ./platform/telegram/...
go test ./platform/telegram/...          # unit tests use an httptest fake Bot API + an in-process bot-link
go run ./platform/telegram/cmd/validator # needs TELEGRAM_BOT_TOKEN
go run ./platform/telegram/cmd/bot       # needs the bot env above + mTLS cert files
```

## Deploy

`platform/telegram/Dockerfile` builds both binaries on distroless nonroot with two
targets, `validator` and `bot`. In the test contour (`deploy/docker-compose.yml`) the
**validator** runs on the internal network (no VPN); the **bot** keeps a VPN sidecar
for Telegram egress and dials the gateway bot-link by its internal name. The bot-link
mTLS material is generated by `deploy/gen-certs.sh`. In prod the bot runs on a separate
host with native Telegram access and dials the gateway's published bot-link port with
`PROD_` certificates in production.

A real end-to-end Telegram smoke needs a BotFather bot, its token, a public HTTPS Mini
App origin, and the bot container; the unit tests cover the wire format, templates,
deep-links, the validator handlers and the bot-link client/executor without a live bot.
