[camera_avfoundation] Wrappers swift migration - part 6

[RobertOdrowaz]

Migrates camera wrappers as part of flutter/flutter#119109

This (last wrappers related 🎉) PR migrates wrappers to Swift:

• FLTSavePhotoDelegate
• FLTWritableData
• FLTImageStreamHandler
• CameraProperties
• QueueUtils

In line with Swift conventions, the FLT prefixes are removed.

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[RobertOdrowaz]

We used to get AVFoundation and Flutter via camera_avfoundation

[gemini-code-assist]

Code Review

This pull request continues the migration of the camera_avfoundation plugin from Objective-C to Swift, focusing on several wrapper and utility classes like FLTSavePhotoDelegate, FLTWritableData, FLTImageStreamHandler, CameraProperties, and QueueUtils. The migration is well-executed, adhering to Swift conventions by removing the 'FLT' prefixes and adopting modern Swift patterns.

My review includes a few suggestions:

• A potential bug in SavePhotoDelegate where a nil photo data case is not handled, leading to a false success report.
• A correction for misleading documentation in SavePhotoDelegate.swift.
• A recommendation to use preconditionFailure instead of assertionFailure in CameraProperties.swift for a known invalid input to ensure robustness in release builds.

[gemini-code-assist]

There's a potential issue in handlePhotoCaptureResult. If photoDataProvider() returns nil, data?.write(...) does nothing, and no error is thrown. The function then proceeds to call strongSelf.completionHandler(strongSelf.path, nil), incorrectly signaling success even though no file was written. This could lead to problems on the Dart side, which would expect a file at the specified path. You should handle the case where data is nil by reporting an error.

        guard let data = photoDataProvider() else {
          let error = NSError(
            domain: "camera_avfoundation",
            code: 0,
            userInfo: [NSLocalizedDescriptionKey: "Failed to get photo data representation."])
          strongSelf.completionHandler(nil, error)
          return
        }
        try data.write(to: strongSelf.path, options: .atomic)
        strongSelf.completionHandler(strongSelf.path, nil)

[RobertOdrowaz]

There seems to be now way to test an assertionFailure. getAVCaptureFlashMode could throw a normal exception but then it would require some handling/assertion in the DefaultCamera for case that never actually happens. I don't think this part of the test provides enough value to justify more changes in this PR