# Design: Multi-Device Equalizer

## Technical Approach

Add a device dimension to the existing 2-level EQ resolution (station > global) by introducing a platform channel bridge for device detection, a Dart service abstraction, and extending `EstadoEcualizador` to resolve through a 4-level hierarchy. Follows existing project patterns: ChangeNotifier state, SharedPreferences persistence via `ServicioEcualizador`, platform channels in `MainActivity.kt`, and constructor-injected fakes for testing.

## Architecture Decisions

### ADR-1: Platform Channel vs Package
**Decision**: Custom platform channel `pluriwave/audio_devices`
- Rationale: Project already has 3 platform channels. Pattern is established. BT MAC from `AudioManager.getDevices()` requires no extra permission.

### ADR-2: Device Service as Abstract Class
**Decision**: Abstract `ServicioDispositivoAudio` with real + fake implementations
- Rationale: Testable without platform channels. Matches existing service pattern.

### ADR-3: Composite Key for Matrix Persistence
**Decision**: `"stationUuid:deviceId"` string key in flat map
- Rationale: Simple serialization. ~80 bytes/entry, predictable SP size.

### ADR-4: Resolution Wiring Point
**Decision**: `EstadoEcualizador` subscribes and resolves internally
- Rationale: Single owner of resolution logic. Handler stays thin and testable.

### ADR-5: EQ Re-application After `_recrearPlayer()`
**Decision**: State layer keeps `_presetActual` updated on device/station change
- Rationale: Handler unchanged. State layer ensures `_presetActual` is always resolved.

### ADR-6: Feature Toggle Scope
**Decision**: SP key `eq_multi_device_enabled_v1` read by `EstadoEcualizador`
- Rationale: Zero behavioral change when off. Toggle at state layer fully isolates feature.

## Data Flow

```
Platform (Android/iOS)
        |
AudioDeviceCallback / routeChangeNotification
        |
EventChannel: pluriwave/audio_devices
        |
ServicioDispositivoAudio (Stream<DispositivoAudio>)
        |
EstadoEcualizador (4-level resolution: matrix > station > device > global)
        |
aplicarPresetActivo(resolved)
        |
ServicioAudio + ServicioEcualizador
```

## File Changes

19 files modified or created:
- `lib/modelos/dispositivo_audio.dart` (NEW)
- `lib/servicios/servicio_dispositivo_audio.dart` (NEW)
- `android/app/src/main/kotlin/.../MainActivity.kt` (MODIFIED)
- `ios/Runner/AudioDevicesPlugin.swift` (NEW)
- `ios/Runner/AppDelegate.swift` (MODIFIED)
- `lib/servicios/servicio_ecualizador.dart` (MODIFIED)
- `lib/estado/estado_ecualizador.dart` (MODIFIED)
- `lib/servicios/servicio_export_import.dart` (MODIFIED)
- `lib/pantallas/pantalla_ajustes.dart` (MODIFIED)
- `lib/l10n/app_en.arb` (MODIFIED)
- `lib/l10n/app_es.arb` (MODIFIED)
- `test/` — 8 new/extended test files

(See Engram observation #2187 for complete design document with all interfaces and contracts)