Move UiState management and extension functions out of PreviewViewModel

[davidjiagoogle]

CaptureUiStateAdapter, QuickSettingsUiStateAdapter, DebugUiStateAdapter are created to create/update UiStates. Extension functions are turned into companion functions of the appropriate model/setting.

This reduces PreviewViewModel code by 270 lines

[gemini-code-assist]

Summary of Changes

Hello @davidjiagoogle, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on a significant refactoring effort to improve the modularity and maintainability of the camera application's UI state management. By moving UiState creation and update logic, along with several utility functions, out of the PreviewViewModel and into dedicated adapter classes and companion objects, the ViewModel becomes leaner and its responsibilities are more clearly defined. This change enhances code organization and makes future development and debugging more straightforward.

Highlights

• Refactoring PreviewViewModel: The core logic for managing and updating UiState has been extracted from PreviewViewModel into dedicated adapter classes and companion functions, significantly reducing the ViewModel's complexity.
• New UiState Adapters: New adapter files, CaptureUiStateAdapter.kt and QuickSettingsUiStateAdapter.kt, have been introduced to centralize the creation and update logic for CaptureUiState and QuickSettingsUiState respectively.
• Extension Functions Relocation: Several extension functions, such as applyDiffs (for CameraAppSettings) and toCaptureMode (for ExternalCaptureMode), have been moved into companion object blocks of their respective classes (CameraSystem and ExternalCaptureMode) to improve encapsulation and organization.
• DebugUiState Logic Externalized: The logic for creating DebugUiState has been moved from PreviewViewModel to DebugUiStateAdapter.kt, further decoupling UI state generation from the ViewModel.

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[gemini-code-assist]

Code Review

This pull request is an excellent refactoring effort that significantly improves the architecture by moving UI state management logic and various helper functions out of the PreviewViewModel. Creating dedicated CaptureUiStateAdapter, QuickSettingsUiStateAdapter, and DebugUiStateAdapter components, and relocating extension functions to their relevant model or companion objects, makes the PreviewViewModel much cleaner and more focused. This change aligns well with the repository's style guide, particularly the principles of architectural consistency and decomposing large components, which enhances code readability, testability, and maintainability. I have one suggestion to further improve the immutability and clarity of the new adapter code.