Drawing an upright stamp annotation on a rotated page

func addUprightStampAnnotation () {
    // We need to fetch the pageInfo for the page in which the stamp annotation needs to be drawn.
    let pageInfo = document.pageInfoForPage(at: 0)
    
    // Here, we get the rotation of the page and convert it to radians.
    let rotation = CGFloat((pageInfo!.rotationOffset.rawValue + pageInfo!.savedRotation.rawValue) % 360) * CGFloat.pi / 180

    let image: UIImage = UIImage.init(named: "stamp-image")!
    let stampAnnotation = PSPDFStampAnnotation()
    stampAnnotation.boundingBox = CGRect(x: 200, y: 200, width: 50, height: 50)
    
    let appearanceStreamGenerator = PSPDFFileAppearanceStreamGenerator(fileURL: URL(fileURLWithPath: ""))
    appearanceStreamGenerator.drawingBlock = { context in
        var transform = CGAffineTransform.identity
        // First translate and go to the center of the stamp annotation
        transform = transform.translatedBy(x: stampAnnotation.boundingBox.origin.x + (stampAnnotation.boundingBox.size.width / 2),
                                           y: stampAnnotation.boundingBox.origin.y + (stampAnnotation.boundingBox.size.height / 2))
        // Now rotate the context in the opposite direction of the page rotation
        transform = transform.rotated(by: -1 * rotation)
        // Translate back to origin
        transform = transform.translatedBy(x: -1 * (stampAnnotation.boundingBox.origin.x + (stampAnnotation.boundingBox.size.width / 2)),
                                           y: -1 * (stampAnnotation.boundingBox.origin.y + (stampAnnotation.boundingBox.size.height / 2)))
        context.concatenate(transform)
        // Draw the image now
        context.draw(image.cgImage!, in: stampAnnotation.boundingBox)
    }
    stampAnnotation.appearanceStreamGenerator = appearanceStreamGenerator
    document.add(annotations: [stampAnnotation])
}