# Exploration: Multi-Device Equalizer

## Current State

- Per-station EQ exists: `Map<String, PresetEcualizador>` in SharedPreferences keyed by station UUID
- No device detection or per-device EQ
- EQ is Android-only via `just_audio`'s `AndroidEqualizer`
- 3 existing platform channels in `MainActivity.kt` (visualizer, alarm, file_actions)
- `ServicioAudioSession` handles interruptions/becoming-noisy only — no device identity

## Key Findings

1. **EQ must be swapped in software** on device change — no native per-device EQ hook exists
2. **BT MAC available** via `AudioManager.getDevices()` → `AudioDeviceInfo.getAddress()` (API 23+). Does NOT require `BLUETOOTH_CONNECT` permission
3. **`_recrearPlayer()` resets AndroidEqualizer** on every source change — re-application must use device+station resolved preset
4. **iOS EQ is a no-op** but device tracking via `AVAudioSession.currentRoute` is possible
5. **No Flutter package covers this** — `flutter_audio_output` is unmaintained, `audio_session` lacks device identity

## Recommended Approach

Custom platform channel `pluriwave/audio_devices` (Approach A):
- Android: `AudioManager.getDevices()` + `AudioDeviceCallback`
- iOS: `AVAudioSession.currentRoute` + `routeChangeNotification`
- Dart bridge: `ServicioDispositivoAudio` with `Stream<DispositivoAudio>` and `Future<List<DispositivoAudio>>`

## Resolution Hierarchy

```
1. presetsMatriz["stationUuid:deviceId"]   ← station × device (most specific)
2. presetsEmisoraMap[stationUuid]           ← station-only (existing)
3. presetsDispositivo[deviceId]             ← device-only
4. presetPrincipal                          ← global default (existing)
```

## Persistence

New SharedPreferences keys (additive):
- `eq_multi_device_enabled_v1` → bool
- `eq_preset_por_dispositivo_v1` → JSON Map<deviceId, preset>
- `eq_presets_matriz_v1` → JSON Map<"stationUuid:deviceId", preset>

## Affected Files

| Area | Files |
|------|-------|
| Model | NEW `dispositivo_audio.dart` |
| Service | NEW `servicio_dispositivo_audio.dart`, extend `servicio_ecualizador.dart`, extend `servicio_audio.dart`, extend `servicio_export_import.dart` |
| State | Extend `estado_ecualizador.dart` |
| Native | Extend `MainActivity.kt`, NEW `AudioDevicesPlugin.swift` |
| UI | Extend `pantalla_ajustes.dart` |
| Tests | Extend existing + new test files |

## Risks

- Android minSdk must be ≥ 23 (likely already gated by AndroidEqualizer)
- iOS uid instability: use `portType+portName` as fallback key
- Backup v3 import must degrade gracefully in v2 builds
- Feature toggle OFF = zero regression invariant