# btcprice

Bitcoin price tracker UI. Serves an HTML page with live price updates streamed from
[btcdata](../btcdata), which this server proxies over WebSocket and renders as HTML fragments
for HTMX.

## Quick Start

```bash
# Start btcdata first (provides price data)
cd ../btcdata && make run

# Local dev — creates .venv and installs requirements on first run
make run       # starts on port 4000
make tailwind  # watch Tailwind CSS (separate terminal)
```

Optionally `cp .env.example .env` to override `BTCDATA_URL`; without it the code default
(`http://localhost:4100`) applies. `make run-local` requires a `.env` defining
`BTCDATA_LOCAL_URL`.

## Docker

`docker compose up -d` starts **btcprice only** — it does not bring up btcdata. Both compose
files attach to the external `btc-network`, so create it once and start btcdata separately:

```bash
docker network create btc-network      # once
cd ../btcdata && docker compose up -d
cd ../btcprice && docker compose up -d
```

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

Inside `btc-network`, btcprice reaches btcdata as `http://btcdata:4102`.

## Environment Variables

| Variable | Default | Description |
|---|---|---|
| `BTCDATA_URL` | `http://localhost:4100` | btcdata service URL the server proxies to |
| `BTCDATA_LOCAL_URL` | — | Used by `make run-local` instead of `BTCDATA_URL` |
| `DOCKER_BTCDATA_PORT` | `4102` | btcdata's port inside `btc-network` (compose only) |

The HTTP port is not configurable via environment: `make run` hardcodes 4000 and the Docker
image's `CMD` hardcodes 4040.

## How It Works

The browser loads a page with HTMX and the WebSocket extension, which connects back to
**btcprice** at `/ws/price` and `/ws/strike` — the browser never contacts btcdata directly.

Each of those endpoints opens an upstream WebSocket to btcdata (`/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 to the browser. HTMX swaps the received
`<div id="price-display">` / `<div id="strike-display">` into the DOM. Price changes are
color-coded (green up, red down). Reconnection is handled by HTMX.

## Tech Stack

Python · FastAPI · Uvicorn · websockets · HTMX · Tailwind CSS v4

The Clojure implementation this replaced is on the `clojure` branch.