QR Scanner view implemented with delegates

gistfile1.txt

import UIKit
import AVFoundation

enum QRScannerError: Error {
    case deviceNotSupported
    case permissionError(Error?)
    case noQrFound
}
/// Delegate callback for the QRScannerView.
protocol QRScannerViewDelegate: class {
    func qrScanningDidFail(with error:QRScannerError)
    func qrScanningSucceeded(with qrString: String)
    func qrScanningDidStop()
}

class QRScannerView: UIView {
    weak var delegate: QRScannerViewDelegate? {
        didSet {
            if scannerAvailable == false {
                delegate!.qrScanningDidFail(with: .deviceNotSupported)
            }
        }
    }

    var scannerAvailable: Bool {
        let devices = AVCaptureDevice.DiscoverySession(deviceTypes: [.builtInDuoCamera, .builtInTelephotoCamera, .builtInWideAngleCamera], mediaType: .video, position: .back).devices
        return devices.first != nil
    }
    /// capture settion which allows us to start and stop scanning.
    var captureSession: AVCaptureSession?
    // Init methods..
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        if scannerAvailable {
            doInitialSetup()
        }
    }
    override init(frame: CGRect) {
        super.init(frame: frame)
        if scannerAvailable {
            doInitialSetup()
        }
    }
    
    //MARK: overriding the layerClass to return `AVCaptureVideoPreviewLayer`.
    override class var layerClass: AnyClass  {
        return AVCaptureVideoPreviewLayer.self
    }
    
    override var layer: AVCaptureVideoPreviewLayer {
        return super.layer as! AVCaptureVideoPreviewLayer
    }
}

extension QRScannerView {
    
    public var isRunning: Bool {
        return captureSession?.isRunning ?? false
    }
    
    public func startScanning() {
        AVCaptureDevice.requestAccess(for: .video) { [weak self] success in
            if success {
                self?.captureSession?.startRunning()
            } else {
                self?.delegate?.qrScanningDidFail(with: .permissionError(nil))
            }
        }
    }
    
    public func stopScanning() {
        captureSession?.stopRunning()
        delegate?.qrScanningDidStop()
    }
    
    /// Does the initial setup for captureSession
    private func doInitialSetup() {
        clipsToBounds = true
        captureSession = AVCaptureSession()
        
        guard let videoCaptureDevice = AVCaptureDevice.default(for: .video) else { return }
        let videoInput: AVCaptureDeviceInput
        do {
            videoInput = try AVCaptureDeviceInput(device: videoCaptureDevice)
        } catch let error {
            print(error)
            delegate?.qrScanningDidFail(with: .permissionError(error))
            return
        }
        
        if (captureSession?.canAddInput(videoInput) ?? false) {
            captureSession?.addInput(videoInput)
        } else {
            scanningDidFail()
            return
        }
        
        let metadataOutput = AVCaptureMetadataOutput()
        
        if (captureSession?.canAddOutput(metadataOutput) ?? false) {
            captureSession?.addOutput(metadataOutput)
            
            metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
            metadataOutput.metadataObjectTypes = [.qr, .ean8, .ean13, .pdf417]
        } else {
            scanningDidFail()
            return
        }
        
        self.layer.session = captureSession
        self.layer.videoGravity = .resizeAspectFill
        
        captureSession?.startRunning()
    }
    
    func scanningDidFail() {
        delegate?.qrScanningDidFail(with: .noQrFound)
        captureSession = nil
    }
    
    func found(code: String) {
        delegate?.qrScanningSucceeded(with: code)
    }
}

extension WFQRScannerView: AVCaptureMetadataOutputObjectsDelegate {
    func metadataOutput(_ output: AVCaptureMetadataOutput,
                        didOutput metadataObjects: [AVMetadataObject],
                        from connection: AVCaptureConnection) {
        stopScanning()
        
        if let metadataObject = metadataObjects.first {
            guard let readableObject = metadataObject as? AVMetadataMachineReadableCodeObject else { return }
            guard let stringValue = readableObject.stringValue else { return }
            AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
            found(code: stringValue)
        }
    }
    
}