import SwiftUI

struct TestPage: View {
    @State private var rect: CGRect = .zero
    @State var uiImage: UIImage? = nil
    
    var body: some View {
        VStack {
            HStack {
                Image(systemName: "sun.haze")
                    .font(.title)
                    .foregroundColor(.white)
                Text("Hello, World!")
                    .font(.title)
                    .foregroundColor(.white)
            }
            .padding()
            .background(Color.blue)
            .cornerRadius(8)
            .background(RectangleGetter(rect: $rect))
            .onAppear() {
                
            }
            
            Button(action: {
                self.uiImage = UIApplication.shared.windows[0].rootViewController?.view!.getImage(rect: self.rect)
            }) {
                Text("Button")
                    .padding()
                    .foregroundColor(Color.white)
                    .background(Color.red)
                    .cornerRadius(8)
                
            }
            
            if uiImage != nil {
                VStack {
                    Image(uiImage: self.uiImage!)
                }.background(Color.green)
                    .frame(width: 500, height: 500)
            }
        }
    }
}

struct RectangleGetter: View {
    @Binding var rect: CGRect
    
    var body: some View {
        GeometryReader { geometry in
            self.createView(proxy: geometry)
        }
    }
    
    func createView(proxy: GeometryProxy) -> some View {
        DispatchQueue.main.async {
            self.rect = proxy.frame(in: .global)
        }
        return Rectangle().fill(Color.clear)
    }
}

extension UIView {
    func getImage(rect: CGRect) -> UIImage {
        let renderer = UIGraphicsImageRenderer(bounds: rect)
        return renderer.image { rendererContext in
            layer.render(in: rendererContext.cgContext)
        }
    }
}

struct TestPage_Previews: PreviewProvider {
    static var previews: some View {
        TestPage()
    }
}