Simple camera controller to show the front camera in Swift

CameraController.swift

class CameraController: NSObject{
    var captureSession: AVCaptureSession?
    var frontCamera: AVCaptureDevice?
    var frontCameraInput: AVCaptureDeviceInput?
    var previewLayer: AVCaptureVideoPreviewLayer?
    
    enum CameraControllerError: Swift.Error {
        case captureSessionAlreadyRunning
        case captureSessionIsMissing
        case inputsAreInvalid
        case invalidOperation
        case noCamerasAvailable
        case unknown
    }
    
    func prepare(completionHandler: @escaping (Error?) -> Void){
        func createCaptureSession(){
            self.captureSession = AVCaptureSession()
        }
        func configureCaptureDevices() throws {
            let camera = AVCaptureDevice.default(.builtInWideAngleCamera, for: AVMediaType.video, position: .front)
            
            self.frontCamera = camera
            
            try camera?.lockForConfiguration()
            camera?.unlockForConfiguration()
            
        }
        func configureDeviceInputs() throws {
            guard let captureSession = self.captureSession else { throw CameraControllerError.captureSessionIsMissing }
            
            if let frontCamera = self.frontCamera {
                self.frontCameraInput = try AVCaptureDeviceInput(device: frontCamera)
                
                if captureSession.canAddInput(self.frontCameraInput!) { captureSession.addInput(self.frontCameraInput!)}
                else { throw CameraControllerError.inputsAreInvalid }
                
            }
            else { throw CameraControllerError.noCamerasAvailable }
            
            captureSession.startRunning()
            
        }
        
        DispatchQueue(label: "prepare").async {
            do {
                createCaptureSession()
                try configureCaptureDevices()
                try configureDeviceInputs()
            }
                
            catch {
                DispatchQueue.main.async{
                    completionHandler(error)
                }
                
                return
            }
            
            DispatchQueue.main.async {
                completionHandler(nil)
            }
        }
    }
    func displayPreview(on view: UIView) throws {
        guard let captureSession = self.captureSession, captureSession.isRunning else { throw CameraControllerError.captureSessionIsMissing }
        
        self.previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        self.previewLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        self.previewLayer?.connection?.videoOrientation = .portrait
        
        view.layer.insertSublayer(self.previewLayer!, at: 0)
        self.previewLayer?.frame = view.frame
    }
    
}