//Recognition queue
let textRecognitionWorkQueue = DispatchQueue(label: "TextRecognitionQueue", qos: .userInitiated, attributes: [], autoreleaseFrequency: .workItem)
//Request for text recognition
var textRecognitionRequest: VNRecognizeTextRequest?

//Set textRecognitionRequest from ViewDidLoad
func setTextRequest() {
    textRecognitionRequest = VNRecognizeTextRequest { request, error in
        guard let observations = request.results as? [VNRecognizedTextObservation] else {
            return
        }
        var detectedText = ""
        self.textBlocks.removeAll()
        for observation in observations {
            guard let topCandidate = observation.topCandidates(1).first else { continue }
            detectedText += "\(topCandidate.string)\n"
            //Text block specific for this project
            if let recognizedBlock = self.getRecognizedDoubleBlock(topCandidate: topCandidate.string, observationBox: observation.boundingBox) {
                self.textBlocks.append(recognizedBlock)
            }
        }
        DispatchQueue.main.async {
            self.textView.text = detectedText
            self.removeLoader()
            self.drawRecognizedBlocks()
        }
    }
    //Individual recognition request settings
    textRecognitionRequest!.minimumTextHeight = 0.011 // Lower = better quality
    textRecognitionRequest!.recognitionLevel = .accurate
}

//Call text recognition request handler
func recognizeImage(cgImage: CGImage) {
    textRecognitionWorkQueue.async {
        let requestHandler = VNImageRequestHandler(cgImage: cgImage, options: [:])
        do {
            try requestHandler.perform([self.textRecognitionRequest!])
        } catch {
            DispatchQueue.main.async {
                self.removeLoader()
                print(error)
            }
        }
    }
}

func drawRecognizedBlocks() {
    guard let image = invoiceImage?.image else  { return }
    //transform from documentation
    let imageTransform = CGAffineTransform.identity.scaledBy(x: 1, y: -1).translatedBy(x: 0, y: -image.size.height).scaledBy(x: image.size.width, y: image.size.height)
    //drawing rects on cgimage
    UIGraphicsBeginImageContextWithOptions(image.size, false, 1.0)
    let context = UIGraphicsGetCurrentContext()!
    image.draw(in: CGRect(origin: .zero, size: image.size))
    context.setStrokeColor(CGColor(srgbRed: 1, green: 0, blue: 0, alpha: 1))
    context.setLineWidth(4)
    for index in 0 ..< textBlocks.count {
        let optimizedRect = textBlocks[index].recognizedRect.applying(imageTransform)
        context.addRect(optimizedRect)
        textBlocks[index].imageRect = optimizedRect
    }
    context.strokePath()
    let result = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    invoiceImage?.image = result
}

struct RecognizedTextBlock {
    let doubleValue: Double
    let recognizedRect: CGRect
    var imageRect: CGRect = .zero
}

//UIImageView tap listener
@objc func onImageViewTap(sender: UITapGestureRecognizer) {
    guard let invoiceImage = invoiceImage, let image = invoiceImage.image else {
        return
    }
    //get tap coordinates on image
    let tapX = sender.location(in: invoiceImage).x
    let tapY = sender.location(in: invoiceImage).y
    let xRatio = image.size.width / invoiceImage.bounds.width
    let yRatio = image.size.height / invoiceImage.bounds.height
    let imageXPoint = tapX * xRatio
    let imageYPoint = tapY * yRatio
    //detecting if one of text blocks tapped
    for block in textBlocks {
        if block.imageRect.contains(CGPoint(x: imageXPoint, y: imageYPoint)) {
            showTapAlert(doubleValue: block.doubleValue)
            break
        }
    }
}