# AGENTS.md

Bitcoin price tracker UI — Python FastAPI web application. Serves the HTML/Tailwind UI and
proxies live price data from btcdata over WebSocket.

## Build & Development Commands

- `make run` — Start dev server on port 4000; creates `.venv` and installs `requirements.txt`
  on first run (the `venv` target, keyed off `requirements.txt`)
- `cp .env.example .env` — optional; `.env` is `-include`d, so a missing one is not fatal
- `make run-local` — Same, but with `BTCDATA_URL=$BTCDATA_LOCAL_URL`
- `make tailwind` — Watch Tailwind CSS for changes
- `make test` — Installs test-only dependencies from `requirements-dev.txt` and runs `pytest tests/`
- `make venv` — Bootstrap the virtualenv without starting the server

## Docker

Docker runs alongside local dev on different ports:

| Service  | Local dev      | Docker                               |
|----------|----------------|--------------------------------------|
| btcprice | localhost:4000 | localhost:4041 (container port 4040) |
| btcdata  | localhost:4100 | localhost:4102                       |

`docker compose up -d` here starts **btcprice only**. Both projects attach to the external
`btc-network` (`docker network create btc-network` once), and btcdata must be started from
`../btcdata`. Inside the network btcprice reaches it at `http://btcdata:${DOCKER_BTCDATA_PORT:-4102}`.

The image does not set `BTCDATA_URL`; deployments must provide it. `BUILD_SHA` is embedded as
`APP_VERSION` and exposed at `/api/version`. The port in `CMD` is hardcoded to 4040.

## CI/CD and production

`.gitea/workflows/build.yml` tests pushes to `main` and `v*` tags on the `anvil` Gitea Actions
runner, then publishes immutable linux/amd64 images to
`harbor.pmagnus.cloud/btcprice/btcprice`. It embeds the short Git SHA as `APP_VERSION`.

The build pushes two tags: `main-<timestamp>`, then a companion `main-<timestamp>-<sha>` for
audit. Harbor's vulnerability policy blocks manifest reads while Trivy is still scanning, so
the companion tag is retried until the scan clears. Only the first tag matters for deployment —
the Flux image policy matches `^main-<14 digits>$` — so a failure in that last step costs the
audit tag and nothing else.

Flux image automation updates the manifests in the separate `magnus/deploy` repository and Flux
reconciles k3s. CI has no Kubernetes credentials. Production runs two replicas—one on hostinger and
one on citadel—and is served at https://btcprice.k8s.pmagnus.cloud through ingress-nginx and
hostinger Traefik TLS. Deployment changes belong in `../deploy/apps/btcprice`; do not deploy with
Compose or manual `kubectl apply`.

## Legacy deployment

`./deploy-citadel.sh` — build locally for the remote's arch, `docker save | ssh docker load`,
`docker compose up -d --no-build` in `/home/pmp/apps/btcprice` on citadel (192.168.50.195).
Mirrors `../elprice/deploy-citadel.sh`; no registry.

- `docker-compose.citadel.yml` → remote `docker-compose.yml`; `.env.citadel` → remote `.env`.
- btcdata also runs on citadel, so both attach to the external `btc-network` there and
  `BTCDATA_URL` is `http://btcdata:4102` (service name, not a LAN address). The deploy script
  creates the network on the remote if it is missing.
- Temporary migration fallback at http://192.168.50.195:4041; it is not the production endpoint.

## Architecture

- **Framework:** FastAPI
- **Server:** Uvicorn
- **Templates:** Inline HTML strings + HTMX (WebSocket extension)
- **Styling:** Tailwind CSS v4
- **Data backend:** btcdata (separate service at `BTCDATA_URL`, default `http://localhost:4100`)
- **No database** — all data comes from btcdata
- **Probes:** `/api/health` is process-only liveness; `/api/ready` checks btcdata with a 3-second
  timeout; `/api/version` exposes the build identifier

### btcdata connection

The browser connects only to btcprice: `ws-connect="/ws/price"` and `ws-connect="/ws/strike"`.
Each endpoint runs `_ws_proxy`, which opens an upstream WebSocket to btcdata's `/api/price/ws`
and `/api/strike/ws`, converts each JSON message to an HTML fragment (`price_json_to_html`,
`strike_json_to_html`) and forwards it. `BTCDATA_URL` is the single point of contact;
`_btcdata_ws_url` rewrites its scheme to `ws`/`wss`.

### Recovering from a btcdata restart

htmx's WebSocket extension reconnects only after an abnormal close
(1006/1011/1012/1013); a normal 1000 close means "the server is done" and the panel stays
frozen until the visitor reloads. So a btcdata restart must never reach the browser as a
normal close:

- `_ws_proxy` reconnects upstream behind the still-open browser socket, on the bounded
  `UPSTREAM_RETRY_DELAYS_SECONDS` schedule. An ordinary restart is invisible to the page —
  the last values stay on screen and updates resume.
- A connection that lasted `UPSTREAM_STABLE_SECONDS` resets that schedule, so a long-lived
  page treats a later restart as a fresh outage rather than a continuing one.
- When the schedule runs out, the proxy closes with `BROWSER_RETRY_CLOSE_CODE` (1012) and
  htmx's own backoff takes over. Every server-side exit uses that code; only a browser that
  has already left can see a plain close.
- A payload that cannot be rendered is logged and skipped, not treated as a dead stream.

`tests/test_ws_proxy.py` covers this against a real loopback WebSocket server, including
same-socket recovery across an upstream restart and the retryable close code. The regression
to watch for is a 1000 close after upstream loss.

## Source Layout

btcprice acts as a WebSocket proxy between the browser and btcdata:
1. Browser connects via HTMX WebSocket to `/ws/price` or `/ws/strike`
2. btcprice proxies to btcdata's `/api/price/ws` or `/api/strike/ws`
3. JSON from btcdata is transformed into HTML fragments (in `price_json_to_html` / `strike_json_to_html`)
4. HTMX swaps the HTML into the DOM by matching element IDs (`price-display`, `strike-display`)

### Key Conventions

- Numbers use Danish locale formatting (dots for thousands, commas for decimals) via `da_fmt()`
- Price changes are color-coded: green (up), red (down), gray (unchanged)
- All HTML is built as string concatenation in Python — no template engine