Move UiState management and extension functions out of PreviewViewModel

core/camera/src/main/java/com/google/jetpackcamera/core/camera/CameraSystem.kt

@@ -140,4 +140,50 @@ interface CameraSystem {
             CLEAR_UI
         }
     }
+
+    companion object {
+        /**
+         * Applies an individual camera app setting with the given [settingExtractor] and
+         * [settingApplicator] if the new setting differs from the old setting.
+         */
+        private suspend inline fun <R> CameraAppSettings.applyDiff(
+            new: CameraAppSettings,
+            settingExtractor: CameraAppSettings.() -> R,
+            crossinline settingApplicator: suspend (R) -> Unit
+        ) {
+            val oldSetting = settingExtractor.invoke(this)
+            val newSetting = settingExtractor.invoke(new)
+            if (oldSetting != newSetting) {
+                settingApplicator(newSetting)
+            }
+        }
+
+        /**
+         * Checks whether each actionable individual setting has changed and applies them to
+         * [CameraSystem].
+         */
+        suspend fun CameraAppSettings.applyDiffs(
+            new: CameraAppSettings,
+            cameraSystem: CameraSystem
+        ) {
+            applyDiff(new, CameraAppSettings::cameraLensFacing, cameraSystem::setLensFacing)
+            applyDiff(new, CameraAppSettings::flashMode, cameraSystem::setFlashMode)
+            applyDiff(new, CameraAppSettings::streamConfig, cameraSystem::setStreamConfig)
+            applyDiff(new, CameraAppSettings::aspectRatio, cameraSystem::setAspectRatio)
+            applyDiff(new, CameraAppSettings::stabilizationMode, cameraSystem::setStabilizationMode)
+            applyDiff(new, CameraAppSettings::targetFrameRate, cameraSystem::setTargetFrameRate)
+            applyDiff(
+                new,
+                CameraAppSettings::maxVideoDurationMillis,
+                cameraSystem::setMaxVideoDuration
+            )
+            applyDiff(new, CameraAppSettings::videoQuality, cameraSystem::setVideoQuality)
+            applyDiff(new, CameraAppSettings::audioEnabled, cameraSystem::setAudioEnabled)
+            applyDiff(
+                new,
+                CameraAppSettings::lowLightBoostPriority,
+                cameraSystem::setLowLightBoostPriority
+            )
+        }
+    }
 }

core/model/src/main/java/com/google/jetpackcamera/model/ExternalCaptureMode.kt

@@ -38,5 +38,14 @@ enum class ExternalCaptureMode {
     /**
      * Under this mode, the app is launched by an external intent to capture multiple images.
      */
-    MultipleImageCapture
+    MultipleImageCapture;
+
+    companion object {
+        fun ExternalCaptureMode.toCaptureMode() = when (this) {
+            ImageCapture -> CaptureMode.IMAGE_ONLY
+            MultipleImageCapture -> CaptureMode.IMAGE_ONLY
+            VideoCapture -> CaptureMode.VIDEO_ONLY
+            Standard -> null
+        }
+    }
 }

data/settings/src/main/java/com/google/jetpackcamera/settings/model/CameraAppSettings.kt

@@ -22,6 +22,8 @@ import com.google.jetpackcamera.model.DarkMode
 import com.google.jetpackcamera.model.DebugSettings
 import com.google.jetpackcamera.model.DeviceRotation
 import com.google.jetpackcamera.model.DynamicRange
+import com.google.jetpackcamera.model.ExternalCaptureMode
+import com.google.jetpackcamera.model.ExternalCaptureMode.Companion.toCaptureMode
 import com.google.jetpackcamera.model.FlashMode
 import com.google.jetpackcamera.model.ImageOutputFormat
 import com.google.jetpackcamera.model.LensFacing
@@ -61,4 +63,20 @@ fun CameraSystemConstraints.forCurrentLens(
     cameraAppSettings: CameraAppSettings
 ): CameraConstraints? = perLensConstraints[cameraAppSettings.cameraLensFacing]
 
+/**
+ * updates the capture mode based on the preview mode
+ */
+fun CameraAppSettings.applyExternalCaptureMode(
+    externalCaptureMode: ExternalCaptureMode
+): CameraAppSettings {
+    val requiredCaptureModeOverride = externalCaptureMode.toCaptureMode()
+    return if (requiredCaptureModeOverride == null ||
+        requiredCaptureModeOverride == this.captureMode
+    ) {
+        this
+    } else {
+        this.copy(captureMode = requiredCaptureModeOverride)
+    }
+}
+
 val DEFAULT_CAMERA_APP_SETTINGS = CameraAppSettings()