ISR/CLAUDE.md

# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Rules

- **Always update `README.md`** whenever user-facing behaviour changes (new flags, new endpoints, changed Docker setup, new features). The README is the primary external reference; CLAUDE.md documents internals.
- **Always commit `README.md`** in the same commit as the code changes it documents — never let the README fall behind.

## Project Overview

ISR is a Python audio recording application that captures from multiple simultaneous sources (Icecast/HTTP streams and ALSA soundcard devices) with time-based file splitting. All application code is in two files: `isr.py` (recorder) and `web.py` (archive browser UI).

## Commands

```bash
# Run the recorder
python isr.py                     # uses config.ini
python isr.py myconfig.ini        # custom config file
python isr.py --list-devices      # list available ALSA devices

# Run the web UI
python web.py                          # http://localhost:8080
python web.py --dir recordings         # custom recordings directory
python web.py --port 8888              # custom port
python web.py --threshold 0.03         # loudness threshold (0-1, default 0.05)

# Stop: Ctrl+C (or docker compose down)

# Install dependencies
pip install requests              # for stream recording
pip install numpy soundfile       # for FLAC output and web waveform analysis (optional)

# Docker
docker compose up -d
docker compose logs -f
docker compose down
```

## Architecture

### Audio Backend System
- **AudioDevice** — Dataclass: id, name, channels, sample_rate, backend type
- **AudioBackend** (ABC) — Abstract base for audio capture backends
  - **ALSABackend** — Native ALSA support via `arecord` subprocess (the only backend)
- **ALSAStream** — Context manager that wraps an `arecord` subprocess and reads PCM in a thread
- **AudioSystem** — Discovers available backends, lists devices, resolves device specs

### Recorder Classes
- **BaseRecorder** (ABC) — Common settings, `get_next_split_time()`, `generate_filename()`, `record()` interface
- **StreamRecorder(BaseRecorder)** — Records HTTP/Icecast streams with format auto-detection and OGG/FLAC header injection
- **SoundcardRecorder(BaseRecorder)** — Records from ALSA devices; outputs WAV or FLAC via `_AudioFileWriter`
- **_AudioFileWriter** — Unified write/close interface for wave (WAV) and soundfile (FLAC)
- **RecorderManager** — Loads config, creates recorders, manages threads, handles shutdown

### Key Implementation Details
- ALSA backend spawns `arecord` as a subprocess; raw PCM is read in 100 ms chunks via a reader thread
- Device selection: `default`, `monitor` (loopback), partial name match, or exact `hw:X,Y` ID
- Thread-safe audio buffering with `threading.Lock()`
- OGG/Opus/FLAC headers captured from first ~16 KB of stream and prepended to each split file
- File splits aligned to time period boundaries (`get_next_split_time()`)
- SIGTERM handled in `main()` so Docker `docker compose down` shuts down cleanly
- `RecorderManager._write_status()` atomically writes `recordings/status.json` every 2 s while running; deleted on clean shutdown so the web UI shows no stale active-recording badges

### Web UI (web.py)
- **`GET /`** — Single-page archive table; lists all recordings sorted newest first
- **`GET /api/files`** — JSON list of file metadata (name, size, date, duration, ext, recording flag)
- **`GET /api/analyze?file=<path>`** — RMS loudness analysis for WAV and FLAC files; returns waveform data, loud sections, and duration. Requires `numpy` and `soundfile` for FLAC.
- **`GET /api/status`** — Returns `{"active": [...]}` from `status.json`; used by the UI to animate the REC badge on in-progress files (polled every 5 s)
- **`GET /stream/<path>`** — Serves audio for inline `<audio>` playback with full HTTP Range support (seekable). Responds 206 Partial Content for range requests. Files are served with `Content-Disposition: inline`.
- **`GET /download/<path>`** — Serves audio as a file download (`Content-Disposition: attachment`)
- All paths are validated against the recordings directory to prevent path traversal.

## Configuration

Copy `config.example.ini` to `config.ini`. Each section defines a recording source:
- `type = stream` — HTTP/Icecast stream recording
- `type = soundcard` — ALSA device recording

The `output_directory` value is used as-is: a relative path like `recordings` resolves to `recordings/` next to `isr.py`. No Docker-specific config change is needed — the docker-compose.yml mounts `./recordings` at `/app/recordings` to match this default.

## Docker

Two services share a `./recordings` bind mount:
- `recorder` — runs `isr.py`; volume at `/app/recordings`; mounts `asound.conf` as `/etc/asound.conf`; maps `/dev/snd`; `ipc: host` for dsnoop shared memory; `stop_grace_period: 30s`
- `web` — runs `web.py`; same `./recordings` read-only at `/recordings`; exposes port 8080

**Sharing the soundcard with darkice (or any other ALSA app):**
ALSA `hw:` devices are exclusive. `asound.conf` defines a `dsnoop` virtual device `shared_mic` that both processes use instead:
1. `sudo cp asound.conf /etc/asound.conf` on the host
2. Change darkice config to `device = shared_mic`
3. Set `device = shared_mic` in `config.ini`
4. `ipc: host` in `docker-compose.yml` is already set — required for dsnoop shared memory to cross the container boundary