DocumentOCRRequestProxy.swift

class DocumentOCRRequestProxy: OCRRequestProxy {

    private lazy var ocrRequest: VNRecognizeTextRequest = VNRecognizeTextRequest(completionHandler: ocrRequestHandler)
    private let requestHandler: VNImageRequestHandler
    
    private weak var ocrRequestDelegate: OCRRequestDelegate?
    private let cgImage: CGImage
    
    init(cgImage: CGImage) {
        self.cgImage = cgImage
        requestHandler = VNImageRequestHandler(cgImage: cgImage, options: [:])
        
        ocrRequest.recognitionLevel = .accurate
        ocrRequest.recognitionLanguages = ["en-US", "en-GB"]
        ocrRequest.usesLanguageCorrection = true
        ocrRequest.revision = VNRecognizeTextRequestRevision1
        ocrRequest.progressHandler = progressUpdateHandler
    }
    
    private func progressUpdateHandler(request: VNRequest, fractionCompleted: Double, error: Error?) {
        ocrRequestDelegate?.progressed(fractionCompleted: fractionCompleted)
    }

    func performOCR() {
        do {
            try requestHandler.perform([self.ocrRequest])
        } catch {
            ocrRequestDelegate?.ocrCompleted(result: .failure(OCRError.failedToPerformOCR))
        }
    }

    func setOCRRequestDelegate(_ delegate: OCRRequestDelegate) {
        self.ocrRequestDelegate = delegate
    }

    private func ocrRequestHandler(request: VNRequest, error: Error?) {
        ....
    }
}