metronome/README.md

# Stackable Metronome

A browser **polymetric groove trainer / metronome** — and the design mockup for a
Raspberry Pi Pico hardware build. Stack as many "meter lanes" as you like; each is
its own little metronome with a grouping, subdivision, drum voice and per-beat
pattern. Layering lanes produces polymeter and true ratio polyrhythm.

**Live:** https://metronome.varasys.io

It's a single, self‑contained `index.html` — **zero dependencies**: no framework,
no build step, no bundled or CDN libraries, and nothing fetched at runtime. State
(set lists, the practice log, theme and UI preferences) lives in `localStorage`.

Because nothing loads from the network, you can save the page (`Ctrl`/`⌘`+`S`) and
open it straight from disk to run fully offline. One catch from a local `file://`:
the browser may not persist `localStorage` between sessions, so use **Export all**
(set‑list **⋯** menu) to back up your work.

## Features

- **Meter lanes** — grouping (odd meters), subdivision, a synthesized drum/percussion voice, per‑beat
  on/off pattern (rests), mute, live measure counter.
- **Polyrhythm** — a per‑lane *poly* toggle fits a lane's beats evenly into lane 1's
  bar (e.g. 5‑over‑4, 3‑over‑2).
- **Practice** — gap/mute trainer (play N / mute M bars) and a tempo ramp with a
  start BPM and signed step.
- **Set lists** — named, ordered lists of saved setups; click an item to load it
  (it switches live if you're already playing), **N** loads the next; each play is
  logged for cross‑day comparison.
- **Sharing** — copy a link to your current settings or a whole set list (with an
  optional QR generated by an external service).
- **Theming** — System / Light / Dark.

## The share language

A compact, human‑readable text encodes a full configuration (a *patch*). It's what
goes in a share link, and you can hand‑write or edit it.

### Patch grammar

```
v1 ; t<bpm> [; vol<pct>] [; cd<sec>] [; b<bars>] ; <lane> … [; tr<play>/<mute>] [; rmp<start>/<step>/<every>]
```

| Token | Meaning | Example |
|-------|---------|---------|
| `v1` | format version (always first) | `v1` |
| `t<bpm>` | tempo | `t120` |
| `vol<pct>` | master volume 0–100 | `vol70` |
| `cd<sec>` | time countdown, seconds (auto-advance with Continue) | `cd60` |
| `b<bars>` | segment length in bars (auto-advance with Continue) | `b16` |
| `tr<play>/<mute>` | gap trainer: play N bars, mute M | `tr2/2` |
| `rmp<start>/<step>/<every>` | tempo ramp: start BPM, ±step, every N bars | `rmp80/5/4` |
| `<lane>` | a meter lane (see below) | `kick:4` |

Tokens are joined with `;`. `tr` and `rmp` are omitted when off.

### Lane grammar

```
<sound> : <grouping> [ / <sub> ] [ = <pattern> ] [ ~ ] [ ! ]
```

- **sound** — one of:
  `beep`, `kick`, `snare`, `rim`, `clap`, `hatClosed`, `hatOpen`, `ride`, `crash`,
  `tomLow`, `tomMid`, `tomHigh`, `tambourine`, `cowbell`, `woodblock`, `claves`,
  `jamblock` (unknown → `beep`).
- **grouping** — beats per bar, optionally grouped for odd meters: `4`, `3`,
  `2+2+3`. The first beat of each group is accented.
- **`/sub`** — subdivision: `1` quarter (default), `2` eighth, `3` triplet,
  `4` sixteenth, `6` sextuplet. This also sets how many **pads** each beat splits
  into (a beat becomes `sub` individually‑toggleable steps). Omit for quarter.
- **`=pattern`** — per‑**step** on/off as `x`/`.`, length = beats per bar × `sub`
  (one char per pad). Omit = all on. e.g. `4=.x.x` is a backbeat on 2 & 4;
  `4/4=x..x..x.x...x...` is a sixteenth‑grid pattern. A short pattern whose length
  equals just the beat count is still accepted and expanded across each beat's
  subdivisions (back‑compat).
- **`~`** — polyrhythm: fit this lane's beats evenly into **lane 1's** bar.
- **`!`** — mute the lane.

### Examples

| Patch / lane | What it is |
|---|---|
| `kick:4` | kick on 4 quarter beats |
| `snare:4=.x.x` | snare backbeat (2 & 4) |
| `hatClosed:4/2` | eighth‑note hi‑hats |
| `claves:5~` | 5 evenly across lane 1's bar (5‑over‑4 if lane 1 is `4`) |
| `kick:2+2+3=x..x..x` | 7/8, kick on each group start |
| `cowbell:3+2/2` | 5/4 grouped 3+2, eighth subdivision |
| **Full:** `v1;t120;kick:4;snare:4=.x.x;hatClosed:4/2;tr2/2` | backbeat groove with gap trainer |

### In URLs

- **Settings:** `…/#p=<patch>` — readable, e.g.
  `…/#p=v1;t120;kick:4;claves:5~`
- **Set list:** `…/#sl=<base64url>` — a JSON `{title, description, items[]}` where
  each item's config is a patch string. Used because titles/notes are free text.

Opening such a link applies the settings (or imports the set list) on load, then
clears the hash so a refresh won't re‑import.

## Sharing

In the set‑list panel's **⋯** menu:
- **Share settings link** / **Share set‑list link** open a dialog with the link to
  **Copy** or **Open**.
- **QR ↗** opens a third‑party QR service (api.qrserver.com) with the link in its
  URL so you can scan it on a phone. A banner warns you it's external — confirm the
  QR decodes to the shown link before trusting it. (No QR is generated locally.)
- **Export all / Import file** back up your set lists and practice log as a JSON
  file (a legacy `presets` field is included for backward compatibility).

## Keyboard shortcuts

| Key | Action |
|-----|--------|
| `Space` | play / stop (works everywhere except while typing in a text field) |
| `T` | tap tempo |
| `←` / `→` | tempo ±1 (`Shift` = ±10) |
| `A` | add meter lane |
| `↑` / `↓` / `Home` / `End` | move the **cue** cursor (crosses set lists) |
| `PgUp` / `PgDn` | cue the previous / next set list |
| `Enter` | commit the cued item — switches on the next **bar** (smooth) |
| `Shift`+`Enter` | commit now — switches on the next **beat** (rude) |
| `N` / `P` | load next / previous immediately (rude quick‑step) |
| `Alt`+`↑` / `Alt`+`↓` | reorder the cued item |
| `1`–`9` | enable / silence lane 1–9 |
| `?` | shortcuts help |
| `Esc` | close the help / share dialog · cancel an armed switch |

(Arrow / navigation keys are left alone while a slider or dropdown is focused, so they still adjust it.)

## Live performance

The set list is performance-ready: you can line up where you're going next without
disturbing what's playing, then commit on a musical boundary — no audible gap.

- **Cue, then commit.** The arrows / `Home` / `End` / `PgUp` / `PgDn` move a *cue
  cursor* (amber outline) through items — across set lists, without loading anything.
  **`Enter`** commits the cued item with a **smooth** cutover at the next **bar**;
  **`Shift`+`Enter`** is a **rude** cutover at the next **beat** ("wrong thing playing,
  fix it now"). `N` / `P` are immediate rude quick‑steps. `Esc` cancels an armed switch.
- **Bar‑length segments.** Give an item a **bar** count (Timers box, or the `b<n>`
  patch token) and a bar countdown (▦) shows bars remaining. With **Continue** on, it
  auto‑advances to the next item at the bar boundary — so a *song* is just a set list
  of segments (each with its own tempo, ramp and bar length) that hand off seamlessly.
- All transitions — manual or auto, beat or bar — keep the clock continuous; the loaded
  item can even live in a set list you're not currently viewing (the player names it).

## Versioning

`VERSION` holds the formal version. `deploy.sh` stamps the served page:

- **Formal** — a clean commit tagged `v<VERSION>` → `X.Y.Z`.
- **Dev** — anything else → `X.Y.Z-dev.<utc-timestamp>.<short-sha>[.dirty]`.

Cut a release with `./release.sh [X.Y.Z]` — the optional arg bumps & commits
`VERSION`; it then tags the current commit `v<VERSION>` (requires a clean tree).
Push the tag, then deploy.

## Deploy

`./deploy.sh` copies `index.html` (version‑stamped) into the Caddy
web root and smoke‑tests the live URL. No restart needed (`file_server` picks up
changes immediately).

## Files

| File | Purpose |
|------|---------|
| `index.html` | the whole app |
| `deploy.sh` | publish to the Caddy web root |
| `release.sh` | tag a formal version |
| `VERSION` | formal version string |
| `LICENSE` | GNU AGPL v3 license text |

## License

Copyright (C) 2026 Varasys.

This program is free software: you can redistribute it and/or modify it under
the terms of the **GNU Affero General Public License** as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version. See [`LICENSE`](LICENSE) for the full text.

Because the app is served over a network, the AGPL's §13 applies: anyone
interacting with a hosted instance must be able to get its source. The repo
link in the in‑app **?** help satisfies this.