VNScannerController.swift

import Foundation
import AVFoundation
import UIKit
import Vision

final class VNScannerController: UIViewController, AVCaptureVideoDataOutputSampleBufferDelegate {
    private let session = AVCaptureSession()
    private let seqHandler = VNSequenceRequestHandler()
    private let captureDevice = AVCaptureDevice.default(for: AVMediaType.video)
    private var request: VNDetectBarcodesRequest?
    private var previewLayer: AVCaptureVideoPreviewLayer!
    private var originalHeight: CGFloat = .zero

    override func viewDidLoad() {
        super.viewDidLoad()
        setUpScanner()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        #if targetEnvironment(simulator)
        #else
            if previewLayer == nil {
                setUpPreviewLayer()
            }
        #endif
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        start()
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        stop()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        previewLayer?.frame = view.bounds
    }
  
    func turnLightOn(_ on: Bool) {
        #if targetEnvironment(simulator)
        #else
            let torchLevel = on ? min(1, AVCaptureDevice.maxAvailableTorchLevel) : 0

            guard let captureDevice = captureDevice,
                  UIApplication.shared.applicationState == .active,
                  captureDevice.hasFlash,
                  captureDevice.torchLevel != torchLevel
            else { return }

            do {
                try captureDevice.lockForConfiguration()
                if on {
                    try captureDevice.setTorchModeOn(level: torchLevel)
                } else {
                    captureDevice.torchMode = .off
                }
                captureDevice.unlockForConfiguration()
            } catch {}

        #endif
    }

    private func start() {
        guard session.isRunning == false else {
            return
        }
        DispatchQueue.global(qos: .userInitiated).async {
            self.session.startRunning()
        }
    }

    private func stop() {
        guard session.isRunning else {
            return
        }
        turnLightOn(false)
        DispatchQueue.global(qos: .userInitiated).async {
            self.session.stopRunning()
        }
    }

    private func setUpPreviewLayer() {
        previewLayer = AVCaptureVideoPreviewLayer(session: session)

        previewLayer.frame = view.layer.bounds
        previewLayer.videoGravity = .resizeAspectFill
        view.layer.addSublayer(previewLayer)
    }

    private func setUpScanner() {
        session.sessionPreset = .high
        try? captureDevice?.lockForConfiguration()
        captureDevice?.focusMode = .continuousAutoFocus
        try? captureDevice?.unlockForConfiguration()
        do {
            try setUpSession()
        } catch {
            print(error)
        }

        request = VNDetectBarcodesRequest { request, _ in
            guard let observations = request.results,
                  observations.isEmpty == false else {
                return
            }
            observations
                .compactMap { $0 as? VNBarcodeObservation }
                .forEach { barcodeObservation in
                    print(barcodeObservation.payloadStringValue)
                }
        }
    }

    private func setUpSession() throws {
        guard let captureDevice else {
            return
        }

        let deviceInput: AVCaptureDeviceInput
        deviceInput = try AVCaptureDeviceInput(device: captureDevice)

        let deviceOutput = AVCaptureVideoDataOutput()
        deviceOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)]
        deviceOutput.setSampleBufferDelegate(self, queue: DispatchQueue.global(qos: .default))
        session.addInput(deviceInput)
        if session.canAddOutput(deviceOutput) {
            session.addOutput(deviceOutput)
        } else {
            throw ScanError.badOutput
        }
    }

    // MARK: Implementing AVCaptureVideoDataOutputSampleBufferDelegate

    func captureOutput(_: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from _: AVCaptureConnection) {
        // https://stackoverflow.com/questions/51214586/value-of-type-cmsamplebuffer-has-no-member-imagebuffer
        guard let pixelBuffer: CVPixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
            return
        }

        guard let request = request else {
            return
        }
        try? seqHandler.perform([request], on: pixelBuffer)
    }
}