Persist torch state while the app is open (#95)

app/src/main/java/org/fairscan/app/ui/screens/camera/CameraScreen.kt

@@ -122,7 +122,7 @@ fun CameraScreen(
     val document by viewModel.documentUiModel.collectAsStateWithLifecycle()
     val thumbnailCoords = remember { mutableStateOf(Offset.Zero) }
     var isDebugMode by remember { mutableStateOf(false) }
-    var isTorchEnabled by remember { mutableStateOf(false) }
+    val isTorchEnabled by cameraViewModel.isTorchEnabled.collectAsStateWithLifecycle()
 
     BackHandler { navigation.back() }
 
@@ -130,6 +130,9 @@ fun CameraScreen(
     DisposableEffect(Unit) {
         onDispose { captureController.shutdown() }
     }
+    LaunchedEffect(captureController.cameraControl, isTorchEnabled) {
+        captureController.cameraControl?.enableTorch(isTorchEnabled)
+    }
 
     val captureState by cameraViewModel.captureState.collectAsStateWithLifecycle()
     if (captureState is CaptureState.CapturePreview) {
@@ -197,8 +200,8 @@ fun CameraScreen(
         onFinalizePressed = onFinalizePressed,
         onDebugModeSwitched = { isDebugMode = !isDebugMode },
         onTorchSwitched = {
-            isTorchEnabled = !isTorchEnabled
-            captureController.cameraControl?.enableTorch(isTorchEnabled) },
+            cameraViewModel.setTorchEnabled(!isTorchEnabled)
+        },
         thumbnailCoords = thumbnailCoords,
         navigation = navigation,
         captureController

app/src/main/java/org/fairscan/app/ui/screens/camera/CameraViewModel.kt

@@ -63,6 +63,9 @@ class CameraViewModel(appContainer: AppContainer): ViewModel() {
     private val _captureState = MutableStateFlow<CaptureState>(CaptureState.Idle)
     val captureState: StateFlow<CaptureState> = _captureState
 
+    private val _isTorchEnabled = MutableStateFlow(false)
+    val isTorchEnabled: StateFlow<Boolean> = _isTorchEnabled
+
     init {
         viewModelScope.launch {
             imageSegmentationService.initialize()
@@ -170,6 +173,10 @@ class CameraViewModel(appContainer: AppContainer): ViewModel() {
             logger.e("Camera", message, throwable)
         }
     }
+
+    fun setTorchEnabled(enabled: Boolean) {
+        _isTorchEnabled.value = enabled
+    }
 }
 
 sealed class CaptureState {