ocrRequestHandler.swift

private func ocrRequestHandler(request: VNRequest, error: Error?) {
    guard let observations = request.results as? [VNRecognizedTextObservation] else { return }
        
    var ocrCandidates: [OCRCandidate] = []
    for observation in observations {
        guard let topCandidate = observation.topCandidates(1).first else { return }
            
        // Vision algorithms use a coordinate system with lower left origin.
        // Converting to upper left so the y values are increasing as the bounding box for observation
        // goes down the list as to how humans read english text.
        let transform = CGAffineTransform(scaleX: 1, y: -1).translatedBy(x: 0, y: -1)

        let boundingPoints = OCRCandidate.BoundingPoints(bottomLeft: observation.bottomLeft.applying(transform),
                                                         bottomRight: observation.bottomRight.applying(transform),
                                                         topRight: observation.topRight.applying(transform),
                                                         topLeft: observation.topLeft.applying(transform))
            
        ocrCandidates.append(.init(text: topCandidate.string, boundingPoints: boundingPoints))
    }

    if ocrCandidates.isEmpty {
        ocrRequestDelegate?.ocrCompleted(result: .failure(OCRError.noTextFound))
    } else {
        let sortedOCRCandidates = ocrCandidates.sortCandidates()
        ocrRequestDelegate?.ocrCompleted(result: .success(sortedOCRCandidates))
    }
}