VisionScannerViewController.swift

import UIKit
import AVFoundation
import Vision

// Note: Please be sure to set the NSCameraUsageDescription key in the project's Info.plist file.

class VisionScannerViewController: UIViewController {
    
    private let captureSession = AVCaptureSession()
    private var barcodeRequest: VNDetectBarcodesRequest?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupBarcodeRequest()
        setupCaptureSession()
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        captureSession.startRunning()
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        captureSession.stopRunning()
    }
}

// MARK: - AVCaptureVideoDataOutputSampleBufferDelegate
extension VisionScannerViewController: AVCaptureVideoDataOutputSampleBufferDelegate {
    func captureOutput(_ output: AVCaptureOutput,
                       didOutput sampleBuffer: CMSampleBuffer,
                       from connection: AVCaptureConnection) {
        guard let barcodeRequest = barcodeRequest,
              let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
            return
        }
        
        let imageRequestHandler = VNImageRequestHandler(
            cvPixelBuffer: pixelBuffer,
            orientation: .right)
        
        do {
            try imageRequestHandler.perform([barcodeRequest])
        } catch {
            // TODO: Handle Error
            print(error)
        }
    }
}

// MARK: - Private Methods
private extension VisionScannerViewController {
    func processBarcodeRequestResults(request: VNRequest, error: Error?) {
        if let error = error {
            // TODO: Error Handling
            print(error)
            return
        }
        
        guard let barcodeObservations = request.results as? [VNBarcodeObservation] else { return }
        for barcodeObservation in barcodeObservations {
            print("payload    : \(barcodeObservation.payloadStringValue ?? "")")
            print("confidence : \(barcodeObservation.confidence)")
            print("symbology  : \(barcodeObservation.symbology)", terminator: "\n\n")
        }
    }
    
    func setupBarcodeRequest() {
        barcodeRequest = VNDetectBarcodesRequest(completionHandler: processBarcodeRequestResults)
        barcodeRequest?.symbologies = [.code128, .qr]
    }
    
    func setupCaptureSession() {
        captureSession.sessionPreset = .hd1280x720
        
        let videoCaptureDevice = AVCaptureDevice
            .default(.builtInWideAngleCamera, for: .video, position: .back)
        guard let device = videoCaptureDevice,
              let captureDeviceInput = try? AVCaptureDeviceInput(device: device),
              captureSession.canAddInput(captureDeviceInput) else {
            return
        }
        captureSession.addInput(captureDeviceInput)
        
        let captureOutput = AVCaptureVideoDataOutput()
        captureOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)]
        captureOutput.setSampleBufferDelegate(self, queue: DispatchQueue.global(qos: DispatchQoS.QoSClass.default))
        captureSession.addOutput(captureOutput)
        
        let capturePreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        capturePreviewLayer.videoGravity = .resizeAspectFill
        capturePreviewLayer.connection?.videoOrientation = .portrait
        capturePreviewLayer.frame = view.frame
        view.layer.insertSublayer(capturePreviewLayer, at: 0)
    }
}