# CLAUDE.md — SLMM (Sound Level Meter Manager)

Device module for **Rion NL-43 / NL-53** sound level meters. Translates
Terra-View's REST calls into the meter's ASCII command protocol over TCP, and
pulls stored data over FTP. Current version: **v0.4.0**.

Stack-level context (which repo owns what, version pairing) lives in
`../terra-view/docs/tmi-stack.md`, which is also loaded as `~/CLAUDE.md`.

**Terra-View never talks to a meter directly** — it always goes through here.
SLMM owns the protocol; Terra-View owns the UI and the measurement records.

---

## Where things stand (updated 2026-08-29)

v0.4.0 (2026-06-22) is the current release. The three things that define the
current design:

- **Fan-out live monitor.** The NL-43 has **one** TCP control connection, and
  every dashboard used to fight for it. Now a single poller reads the device and
  all subscribers share one cached feed: `WS /api/nl43/{unit_id}/monitor`
  delivers an instant first frame from cache, then live updates. Poll rate
  adapts to demand, unreachable devices back off, and the background poller
  skips units already covered by an active monitor so nothing double-polls.
- **Alert engine.** Per-device threshold rules (metric + threshold + cooldown)
  with full CRUD, an onset/clear state machine, and acknowledgement. Enabled
  rules **pin the monitor on**, so they evaluate 24/7 with no UI client
  connected. Editing or deleting a rule resets its state and closes any open
  event.
- **History for chart backfill.** A downsampled trail persists to `nl43_readings`
  and is served from `GET /api/nl43/{unit_id}/history`, so live charts can fill
  in recent history on load. L1/L10 percentiles are surfaced in status and the
  live feed.

`CHANGELOG.md` is the authority for anything older; prefer it over prose here.

---

## Changelog & release convention

Adopted 2026-09-18, to match seismo-relay and Terra-View.  SLMM had no written
practice before this — earlier releases used ad-hoc commits like
`chore: version bump`.  This is the standard going forward.

**Write the entry in the same commit as the work, under `## [Unreleased]`.  Cut
the version on `dev` in a dedicated release commit.  Never touch the changelog
at a merge boundary.**

- **Entry goes in with the change**, not at merge or release time — that is the
  only moment you still know *why*.  Feature branches edit `CHANGELOG.md`
  directly; the occasional conflict is two appended bullets and is trivial.
- **No preamble under `## [Unreleased]`** — just the `### Added` / `### Changed`
  / `### Fixed` lists.  The themed opening paragraph gets written at release
  time, when the whole release is visible and can be named honestly.  A theme
  written when the first item landed is stale by the third.
- ⚠ **State the operational consequence**, **including when it is "none."**
  Silence is ambiguous; "none" is information.  For this repo that means:
  - **DB migration** — whether a `migrate_*.py` script is needed, which one,
    and whether it is safe to re-run.  These live at the repo root and are
    easy to forget at deploy time.
  - **Meter-connection impact** — anything touching the NL-43/NL-53 TCP path,
    polling cadence, or the monitor fan-out.  The meter has a **single TCP
    slot**, so a change that bounces the connection is an operational event,
    not just a code change.
- **Cutting a release** is its own `chore(release): vX.Y.Z` commit on `dev`,
  renaming `## [Unreleased]` → `## [X.Y.Z] - YYYY-MM-DD` and bumping the
  version in `app/main.py` (the FastAPI `version=` argument).
- **`main` carries only released versions.**  No `## [Unreleased]` section
  there; it lands via the `dev` → `main` PR.

---

## Layout

```
app/
  main.py              FastAPI app + health checks
  routers.py           all REST endpoints
  services.py          NL43Client — TCP + FTP protocol
  monitor.py           the fan-out live feed
  background_poller.py scheduled polling
  alerts.py            rule evaluation + event state machine
  models.py            NL43Config, NL43Status, nl43_readings
  database.py          SQLAlchemy / SQLite (data/slmm.db)
  device_logger.py
docs/     manuals/     templates/     nl52/     SLM-stress-test/
```

Key docs: `docs/API.md` (endpoint reference with curl examples),
`docs/COMMUNICATION_GUIDE.md` and `docs/nl43_Command_ref.md` (protocol).

---

## API surface

```
GET/PUT /api/nl43/{unit}/config
GET     /api/nl43/{unit}/status            cached snapshot
GET     /api/nl43/{unit}/live              fresh read
POST    /api/nl43/{unit}/{start|stop|pause|resume|reset|store}
GET     /api/nl43/{unit}/{battery|clock|results|settings}
WS      /api/nl43/{unit}/monitor           fan-out live feed
POST    /api/nl43/{unit}/monitor/{start|stop}
GET     /api/nl43/_monitor/status
GET     /api/nl43/{unit}/history           backfill trail
        .../alerts/rules  .../alerts/events  .../events/{id}/ack
POST/GET /api/nl43/{unit}/ftp/{enable|disable|status|files|download}
GET     /api/nl43/{unit}/overwrite-check   BEFORE changing a store name
```

---

## Gotchas

- **One TCP connection per meter.** This is the constraint the whole monitor
  design exists to work around. Never add a code path that opens its own
  connection alongside the monitor.
- **1-second minimum between commands.** The NL-43 protocol requires it; SLMM
  enforces it automatically. Do not "optimise" it away.
- **Check `overwrite-check` before changing a store name** — otherwise you can
  destroy data on the meter's SD card.
- **FTP is active mode** — the device connects *back* to the server on port 21.
- **`network_mode: host`** in compose, for direct network access to meters.
- Environment: `PORT` (8100), `CORS_ORIGINS`, `TIMEZONE_OFFSET`, `TIMEZONE_NAME`.