Mobile Platform Features and Services Questions

import UIKit
import AVFoundation

final class CameraHelper: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    private var completion: ((UIImage?) -> Void)?
    private weak var presentingVC: UIViewController?

    func presentCamera(from vc: UIViewController, completion: @escaping (UIImage?) -> Void) {
        self.presentingVC = vc
        self.completion = completion

        func showPicker() {
            guard UIImagePickerController.isSourceTypeAvailable(.camera) else {
                completion(nil); return
            }
            let picker = UIImagePickerController()
            picker.sourceType = .camera
            picker.cameraCaptureMode = .photo
            picker.delegate = self
            // present on main thread
            DispatchQueue.main.async { vc.present(picker, animated: true) }
        }

        let status = AVCaptureDevice.authorizationStatus(for: .video)
        switch status {
        case .authorized: showPicker()
        case .notDetermined:
            AVCaptureDevice.requestAccess(for: .video) { granted in
                // requestAccess callback is NOT guaranteed main thread
                if granted { showPicker() } else { DispatchQueue.main.async { completion(nil) } }
            }
        default:
            // denied/restricted -> handle by informing user (omitted) and return nil
            completion(nil)
        }
    }

    // MARK: - UIImagePickerControllerDelegate
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        // get original image; do not save to library
        let image = info[.originalImage] as? UIImage
        picker.dismiss(animated: true) {
            // invoke completion on main thread (UI updates here)
            DispatchQueue.main.async { self.completion?(image); self.cleanup() }
        }
    }

    func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
        picker.dismiss(animated: true) {
            DispatchQueue.main.async { self.completion?(nil); self.cleanup() }
        }
    }

    private func cleanup() {
        completion = nil
        presentingVC = nil
    }
}

// Generate AES and wrap with AndroidKeyStore RSA/ECDSA key (high-level pseudo)
val keyPair = generateHardwareKeyPair("alias")
val aesKey = generateAesKey()
val wrapped = wrapKeyWithKeyStorePublic(keyPair.public, aesKey)
storeWrappedKey(wrapped)
val ciphertext = aesGcmEncrypt(aesKey, token)

// Create access control requiring biometrics, store AES key in Keychain
let access = SecAccessControlCreateWithFlags(nil, kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly, .biometryAny, nil)
// store AES key with access control

// Threading
val cameraThread = HandlerThread("CameraThread").apply { start() }
val cameraHandler = Handler(cameraThread.looper)
val ioThread = HandlerThread("IOThread").apply { start() }
val ioHandler = Handler(ioThread.looper)

// Camera selection
fun chooseCamera(manager: CameraManager): String {
  for (id in manager.cameraIdList) {
    val chars = manager.getCameraCharacteristics(id)
    val caps = chars.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES) ?: continue
    if (caps.contains(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES_RAW)) return id
  }
  return manager.cameraIdList.first() // fallback
}

// ImageReaders
val rawReader = ImageReader.newInstance(width, height, ImageFormat.RAW_SENSOR, 2)
val jpegReader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 2)

// Open camera
manager.openCamera(chosenId, object : CameraDevice.StateCallback() {
  override fun onOpened(device: CameraDevice) {
    cameraDevice = device
    createSession()
  }
  override fun onDisconnected(d: CameraDevice) { d.close() }
  override fun onError(d: CameraDevice, err: Int) { d.close() }
}, cameraHandler)

// Create capture session
fun createSession() {
  val targets = listOf(rawReader.surface, jpegReader.surface, previewSurface)
  cameraDevice.createCaptureSession(targets, object: CameraCaptureSession.StateCallback() {
    override fun onConfigured(session: CameraCaptureSession) {
      captureSession = session
      startPreviewWithManualControls()
    }
    override fun onConfigureFailed(s: CameraCaptureSession) {}
  }, cameraHandler)
}

// Build manual request
fun startPreviewWithManualControls() {
  val req = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW).apply {
    addTarget(previewSurface)
    // Manual controls
    set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_OFF)
    set(CaptureRequest.SENSOR_EXPOSURE_TIME, 10_000_000L) // 10ms example
    set(CaptureRequest.SENSOR_SENSITIVITY, 400)
    set(CaptureRequest.LENS_FOCUS_DISTANCE, 0.5f) // manual focus distance
    set(CaptureRequest.STATISTICS_FACE_DETECT_MODE, CaptureRequest.STATISTICS_FACE_DETECT_MODE_SIMPLE)
  }
  captureSession.setRepeatingRequest(req.build(), captureCallback, cameraHandler)
}

// Single RAW+JPEG capture
fun captureRawAndJpeg() {
  val req = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE).apply {
    addTarget(rawReader.surface)
    addTarget(jpegReader.surface)
    set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_OFF)
    // tighten manual exposure for still
    set(CaptureRequest.SENSOR_EXPOSURE_TIME, desiredExposureNs)
    set(CaptureRequest.SENSOR_SENSITIVITY, desiredIso)
    set(CaptureRequest.LENS_FOCUS_DISTANCE, focusDistance)
    // enable RAW if available via target
    set(CaptureRequest.JPEG_ORIENTATION, getOrientation())
  }
  captureSession.capture(req.build(), captureCallback, cameraHandler)
}

// Image processing & software stabilization
rawReader.setOnImageAvailableListener({ reader ->
  val image = reader.acquireNextImage()
  ioHandler.post {
    val rawBuffer = extractRawBuffer(image)
    val stabilized = runSoftwareStabilization(rawBuffer) // custom algorithm: motion estimate + warp
    saveDng(stabilized, image) // write DNG using Exif + metadata
    image.close()
  }
}, cameraHandler)

// Capture callbacks
val captureCallback = object: CameraCaptureSession.CaptureCallback() {
  override fun onCaptureCompleted(session: CameraCaptureSession, request: CaptureRequest, result: TotalCaptureResult) {
    // read AE/AF state, meter extents, update UI
  }
  override fun onCaptureFailed(session: CameraCaptureSession, request: CaptureRequest, failure: CaptureFailure) { }
}