prepare.swift

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)
        }
    }
}