# Plan: Waveform Pre-computation

**Branch:** `feature/waveform-precompute`  
**Goal:** Store waveform peaks in the database during indexing so WaveSurfer renders
the waveform instantly (no waiting for audio decode), and show a mini-waveform in
the library/overview song list.

## Background

WaveSurfer v7 supports `ws.load(url, channelData)` — when pre-computed peaks are
passed as a `Float32Array[]`, the waveform renders immediately and audio streams in
the background. Currently the frontend calls `ws.load(url)` which blocks until the
full audio is decoded.

The worker already generates a 500-point peaks JSON file (`waveform_url`), but:
- It is stored as a file on disk, not inline in the DB
- The frontend never reads it (the `peaksUrl` option in `useWaveform` is wired to
  nothing)

## Architecture Decision

Add two JSONB columns to `audio_versions`:
- `waveform_peaks` — 500 points, returned inline with version data, passed to WaveSurfer
- `waveform_peaks_mini` — 100 points, returned inline, used for SVG mini-waveform in
  library/song list

This eliminates a separate HTTP round-trip and lets the UI render the waveform the
moment the page loads.

---

## Checklist

### Backend

#### B1 — DB: Peaks columns + Alembic migration
- [ ] Write migration test: after upgrade, `audio_versions` table has `waveform_peaks`
      and `waveform_peaks_mini` JSONB columns
- [ ] Create `api/alembic/versions/0006_waveform_peaks_in_db.py`
- [ ] Add `waveform_peaks` and `waveform_peaks_mini` JSONB columns to `AudioVersion`
      model in `api/src/rehearsalhub/db/models.py`

#### B2 — Worker: Generate and store both peak resolutions
- [ ] Write unit tests for `extract_peaks()` in `worker/tests/test_waveform.py`:
  - Returns exactly `num_points` values
  - All values in [0.0, 1.0]
  - Empty audio returns list of zeros (no crash)
  - 100-point and 500-point both work
- [ ] Update `handle_transcode` in `worker/src/worker/main.py`:
  - Generate `peaks_500 = extract_peaks(audio, 500)`
  - Generate `peaks_100 = extract_peaks(audio, 100)`
  - Store both on `AudioVersion` DB row
- [ ] Write integration test: after `handle_transcode`, row has non-null
      `waveform_peaks` (len 500) and `waveform_peaks_mini` (len 100)

#### B3 — API Schema: Expose peaks in `AudioVersionRead`
- [ ] Write serialization test: `AudioVersionRead.model_validate(orm_obj)` includes
      `waveform_peaks: list[float] | None` and `waveform_peaks_mini: list[float] | None`
- [ ] Update `api/src/rehearsalhub/schemas/audio_version.py` — add both fields

#### B4 — API Router: `/waveform` endpoint reads from DB
- [ ] Write endpoint tests:
  - `GET /versions/{id}/waveform` returns `{"data": [...500 floats...]}` from DB
  - `GET /versions/{id}/waveform?resolution=mini` returns 100-point peaks
  - 404 when version has no peaks yet
- [ ] Update `api/src/rehearsalhub/routers/versions.py` — read from
      `version.waveform_peaks` / `version.waveform_peaks_mini` instead of file I/O

#### B5 — API: Peaks inline on versions list (verify, no change expected)
- [ ] Write test: `GET /songs/{id}/versions` response includes `waveform_peaks` and
      `waveform_peaks_mini` on each version object
- [ ] Confirm no router change needed (schema update in B3 is sufficient)

---

### Frontend

#### F1 — Types: Update `AudioVersionRead` TS type
- [ ] Add `waveform_peaks: number[] | null` and `waveform_peaks_mini: number[] | null`
      to the TypeScript version type (wherever API types live)

#### F2 — `audioService`: Accept and use pre-computed peaks
- [ ] Write unit tests for `AudioService.initialize()`:
  - With peaks: calls `ws.load(url, [Float32Array])` → waveform renders immediately
  - Without peaks: calls `ws.load(url)` → falls back to audio decode
  - Same URL + same peaks → no re-initialization
- [ ] Update `AudioService.initialize(container, url, peaks?: number[])` in
      `web/src/services/audioService.ts`:
  - Call `ws.load(url, peaks ? [new Float32Array(peaks)] : undefined)`

#### F3 — `useWaveform` hook: Thread peaks through
- [ ] Write hook test: when `peaks` option is provided, it is forwarded to
      `audioService.initialize`
- [ ] Add `peaks?: number[] | null` to `UseWaveformOptions` in
      `web/src/hooks/useWaveform.ts`
- [ ] Forward `options.peaks` to `audioService.initialize()` in the effect

#### F4 — `PlayerPanel`: Pass peaks to hook
- [ ] Write component test: `PlayerPanel` passes `version.waveform_peaks` to
      `useWaveform`
- [ ] Update `web/src/components/PlayerPanel.tsx` to extract and forward
      `waveform_peaks`

#### F5 — `MiniWaveform`: New SVG component for library overview
- [ ] Write unit tests:
  - Renders SVG with correct number of bars matching peaks length
  - Null/empty peaks renders a grey placeholder (no crash)
  - Accepts `peaks`, `width`, `height`, `color` props
- [ ] Create `web/src/components/MiniWaveform.tsx` — pure SVG, no WaveSurfer
- [ ] Integrate into song list / library view using `waveform_peaks_mini`

---

## Testing Strategy

| Layer            | Tool                                         |
|------------------|----------------------------------------------|
| Backend unit     | pytest, synthetic numpy arrays               |
| Backend integration | Real Postgres via docker-compose test profile |
| Frontend unit    | Vitest + Testing Library                     |
| E2E              | Playwright — assert waveform visible before audio `canplay` fires |

---

## Implementation Order

1. B1 — migration + model  
2. B2 — worker (TDD: unit tests → implementation → integration test)  
3. B3 — schema  
4. B4 — router  
5. B5 — verify versions list  
6. F1 — TS types  
7. F2 — audioService  
8. F3 — useWaveform  
9. F4 — PlayerPanel  
10. F5 — MiniWaveform