btcprice/CLAUDE.md

CLAUDE.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 -included, 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 — Runs pytest tests/, but there is no tests/ directory yet and pytest is not in requirements.txt
• 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}.

Note: Dockerfile bakes in a stale ENV BTCDATA_URL=http://btcdata:4101; compose always overrides it, so it only matters if the image is run outside compose. ENV PORT is likewise unused — the port in CMD is hardcoded.

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

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.

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