Dual Front Camera System

import AVFoundation

final class DuoFrontCameraController: NSObject {
    private let session = AVCaptureSession()
    private var directionObservation: NSKeyValueObservation?
    let previewLayer = AVCaptureVideoPreviewLayer()

    func start() throws {
        // Virtual Front Camera: the system picks outer or inner
        // automatically based on the device's current pose.
        guard let device = AVCaptureDevice.default(.builtInDualWideCamera, for: .video, position: .front) else {
            throw CameraError.unavailable
        }

        let input = try AVCaptureDeviceInput(device: device)
        session.beginConfiguration()
        if session.canAddInput(input) { session.addInput(input) }
        session.commitConfiguration()

        previewLayer.session = session
        previewLayer.videoGravity = .resizeAspectFill

        let rotationCoordinator = AVCaptureDevice.RotationCoordinator(device: device, previewLayer: previewLayer)
        previewLayer.connection?.videoRotationAngle = rotationCoordinator.videoRotationAngleForHorizonLevelPreview

        session.startRunning()
    }
}

enum CameraError: Error { case unavailable }