# VST3 / SoundFont Engine — Implementation Plan

## Current State vs Requirements

| Check | Status | Ref |
|-------|--------|-----|
| FluidSynth Channel 9 for Drums (bank=128) | ✅ Already implemented. `render_engine.py:64` forces `midi_channel=9` when `is_percussion` or `bank==128`. | R1 verify |
| Catalog cache invalidation on SF upload | ✅ Already implemented. `plugins.py:93-95` calls `invalidate_catalog_cache()`. | R2 verify |
| DecentSampler CWD swap for `.wav` samples | ✅ Already implemented. `vst_engine.py:338-341` does `os.chdir(preset_dir)`. | R3 verify |
| FluidSynth SF2 path uses `static/soundfonts/` hardcoded | ❌ `render_engine.py:186-189` hardcodes `static/soundfonts/<id>.sf2`. Must scan system + upload dirs. | **Bug** |
| SF2 upload dir (`app/storage/uploads/soundfonts/`) not searched in render_engine | ❌ FluidSynth render branch never looks at user uploads. | **Bug** |
| `synth_engine` structured metadata not parsed | ❌ Render path uses flat fields only. Spec uses `{type, plugin_id, bank, program}`. | **Gap** |
| Client preview still oscillator-emulated | ⚠️ Acceptable per spec: "Wasm Module / Preview Synth" — no real SF2 in browser. `soundfontPlayer.js` reads flat fields, not `synth_engine`. | **Gap** |
| Host asset permissions might deny Docker | ⚠️ Non-root users may get `Permission Denied` on mounted `.vst3`/`.sf2`. | R4 |
| Missing VST3/SF2 fallback chain | ⚠️ No graceful degraded path if selected instrument is absent. | R5 |

---

## Tasks

### Task A — Environment Validation

1. **Host asset check + permissions**
   - Verify `ls /home/locpham/daw_assets/{vst3,soundfonts,pianobook}/*` returns files
   - `chmod -R 755 /home/locpham/daw_assets`
   - **Files:** host paths only

2. **Docker compose mount verification**
   - `docker-compose.yml:13-15` maps:
     - `vst3` → `/opt/daw_engine/vst3`
     - `soundfonts` → `/opt/daw_engine/soundfonts`
     - `pianobook` → `/opt/daw_engine/samples/pianobook`

3. **Runtime Python deps verification**
   - `docker compose exec web python -c "import pedalboard, fluidsynth; from sf2utils.sf2parse import Sf2File; print('OK')"`
   - Check server logs for `HAS_PEDALBOARD`, `HAS_PYFLUIDSYNTH` flags in `vst_engine.py`

---

### Task B — Fix SF2 Path Resolution (Bugfix)

4. **`render_engine.py` FluidSynth branch** — replace hardcoded `static/soundfonts/` path
   - **Current** (line 185-189): builds path to `app/static/soundfonts/<sf_id>.sf2` only
   - **Target**: search in order:
     1. `UPLOAD_SF_DIR` = `app/storage/uploads/soundfonts/<id>.sf2`
     2. `SYSTEM_SF_DIR` = `/opt/daw_engine/soundfonts/<id>.sf2`
     3. Match by `soundfont_id` field in track metadata (not just filename)
   - Accept both `sf_<id>` and bare `<id>` in `instrument_id`
   - **Files:** `app/core/render_engine.py:185-225`

5. **Read `soundfont_bank`/`soundfont_program` from track in FluidSynth branch**
   - Currently read at lines 61-63 (before item loop) — ✅ correct
   - Ensure `fl.program_select(midi_channel, fid, bank, program)` uses them (line 194) — ✅ correct
   - **Files:** `app/core/render_engine.py` (verify only)

---

### Task C — `synth_engine` Metadata Alignment

6. **`render_engine.py`: parse `synth_engine` object**
   ```python
   se = track.get("synth_engine", {})
   instrument_id = se.get("plugin_id") or track.get("instrument_id", "")
   soundfont_bank = se.get("soundfont_bank") or track.get("soundfont_bank", 0)
   soundfont_program = se.get("soundfont_program") or track.get("soundfont_program", 0)
   instrument_source = se.get("type") or track.get("instrument_source", "soundfont")
   ```
   - Apply before the item loop (around line 57-67)
   - Keep flat fields as fallback for backward compat
   - **Files:** `app/core/render_engine.py`

7. **`app.jsx`: write `synth_engine` alongside flat fields**
   - In `setTrackInstrumentWithProgram()` (line 6490): add `synth_engine: {type, plugin_id, soundfont_bank, soundfont_program}`
   - In `setTrackInstrument()` (line 6540): same
   - Type logic:
     - `instrumentId` starts with `sf_` → `type: "soundfont"`
     - `instrumentId` is VST name → `type: "vst3"`
     - `null` → `type: "default"`
   - **Files:** `app/static/js/app.jsx:6490-6561`

8. **`aiGateway.js`: include `synth_engine` in track context**
   - In `buildAIPromptContext()` (line 218): add `synth_engine` to track objects
   - **Files:** `app/static/js/services/aiGateway.js:218-245`

---

### Task D — Graceful Fallback Chain (R5)

9. **`render_engine.py`: 3-level fallback for missing instruments**
   - Level 1: Selected VST3/SoundFont
   - Level 2: Default `GeneralUser_GS.sf2` (or first available `.sf2`)
   - Level 3: Basic oscillator synth (`render_midi_events_to_audio`)
   - **Files:** `app/core/render_engine.py:131-230`

---

### Task E — Client Playback Enhancement

10. **`soundfontPlayer.js`: read `synth_engine` from track context**
    - `playNote()` accepts optional `synthEngine` param
    - Before scheduling: call `controllerChange(ch, 0, bank)` and `programChange(ch, program)`
    - Use existing oscillator ADSR emulation (no WASM SF2 — scope limit)
    - **Files:** `app/static/js/services/soundfontPlayer.js:82-204`

11. **`app.jsx`: pass `synth_engine` to `SonicSF.playNote`**
    - In `schedulePianoRollMidi()`: read `synth_engine` from active track, forward it
    - **Files:** `app/static/js/app.jsx`

---

### Task F — AI Workflow Verification

12. **Catalog API test**
    - `GET /api/v1/plugins/soundfonts/catalog` returns `{full_catalog, condensed_catalog}`
    - Condensed ≤ 50 entries
    - `window.__soundfontCatalog` populated on app load

13. **AI prompt injection test**
    - `buildCatalogPromptSection()` generates catalog text with bank/program rules
    - Submit: *"Compose 8 bars of Brass horns and a drum kit"*
    - Verify returned JSON: Brass has `bank:0, program:56`, Drums has `bank:128, program:0`

---

### Task G — End-to-End Test

14. **Manual checklist**
    - [ ] `docker compose up --build` succeeds
    - [ ] Synth button shows "Synth" → click → dropdown lists SoundFonts + VSTs
    - [ ] Select SoundFont → button label updates → instrument presets appear
    - [ ] Select preset → label reflects exact instrument name
    - [ ] Draw MIDI notes → Play → oscillator preview (approximate GM sound)
    - [ ] Export WAV → file plays correct FluidSynth/VST3 instrument
    - [ ] Select "None (Default Synth)" → oscillator fallback works
    - [ ] AI generates track with instrument → export plays correct patch
    - [ ] Upload new `.sf2` → appears in dropdown after refresh

---

### Task H — Install Missing Assets (if needed)

15. If `.sf2` absent: copy `GeneralUser_GS.sf2` or `SGM-V2.01.sf2` to `/home/locpham/daw_assets/soundfonts/`
16. If `.vst3` absent: place `DecentSampler.vst3` in `/home/locpham/daw_assets/vst3/`
17. If `.dspreset` absent: place Pianobook library in `/home/locpham/daw_assets/pianobook/`

---

## Affected Files

| File | Changes |
|------|---------|
| `app/core/render_engine.py` | Fix SF2 path resolution (Task B), parse `synth_engine` (Task C), 3-level fallback (Task D) |
| `app/static/js/app.jsx` | Write `synth_engine` in setTrackInstrument functions (Task C), pass to SoundFontPlayer (Task E) |
| `app/static/js/services/soundfontPlayer.js` | Accept `synthEngine` param, dispatch CC/program before note (Task E) |
| `app/static/js/services/aiGateway.js` | Include `synth_engine` in AI track context (Task C) |
| `app/api/v1/plugins.py` | No changes needed (cache invalidation already exists) |
| `app/core/vst_engine.py` | No changes needed (CWD swap already exists) |
| Host `/home/locpham/daw_assets/*` | `chmod 755`, ensure files exist |

## Validation

```bash
# 1. Build & boot
docker compose up --build -d

# 2. Verify deps
docker compose exec web python -c "import pedalboard, fluidsynth; from sf2utils.sf2parse import Sf2File; print('OK')"

# 3. Catalog API
curl -s http://localhost:8000/api/v1/plugins/soundfonts/catalog | python -m json.tool | head -60

# 4. Render smoke test — create minimal project JSON and POST /api/v1/plugins/render
```

## Rollback

All changes backward-compatible (flat fields still work if `synth_engine` absent).
```bash
git checkout -- app/core/render_engine.py app/static/js/app.jsx \
  app/static/js/services/soundfontPlayer.js app/static/js/services/aiGateway.js
```