OTP/OTP/Views/QRCodeView.swift

//
//  QRCodeView.swift
//  OTP
//
//  Created by Shadowfacts on 8/23/21.
//

import SwiftUI
import OTPKit
import CoreImage.CIFilterBuiltins

struct QRCodeView: View {
    let key: TOTPKey
    @State private var image: UIImage?
    @Environment(\.dismiss) private var dismiss
    @State private var isPresentingShareSheet = false
    
    init(key: TOTPKey) {
        self.key = key
//        self._image = State(initialValue: createImage())
    }
    
    private func createImage() -> UIImage? {
        let filter = CIFilter.qrCodeGenerator()
        filter.message = key.url.absoluteString.data(using: .utf8)!
        let transform = CGAffineTransform(scaleX: 5, y: 5)
        
        let context = CIContext()
        guard let output = filter.outputImage?.transformed(by: transform),
           let cgImage = context.createCGImage(output, from: output.extent) else {
            return nil
        }
        
        let issuerFont = UIFont(descriptor: .preferredFontDescriptor(withTextStyle: .largeTitle).withSymbolicTraits(.traitBold)!, size: 0)
        let labelFont = UIFont(descriptor: .preferredFontDescriptor(withTextStyle: .body), size: 0)
        
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineBreakMode = .byWordWrapping
        
        let issuer = key.issuer as NSString
        let size = CGSize(width: CGFloat(cgImage.width - 8), height: .greatestFiniteMagnitude)
        
        var issuerRect = issuer.boundingRect(with: size, options: [.usesFontLeading, .usesLineFragmentOrigin], attributes: [.font: issuerFont, .paragraphStyle: paragraphStyle], context: nil)
        issuerRect.origin.y += 4
        issuerRect.origin.x += 4
        
        var labelRect = CGRect.zero
        if let label = key.label, !label.isEmpty {
            labelRect = (label as NSString).boundingRect(with: size, options: [.usesFontLeading, .usesLineFragmentOrigin], attributes: [.font:  labelFont, .paragraphStyle: paragraphStyle], context: nil)
            labelRect.origin.x += 4
            labelRect.origin.y += ceil(issuerRect.maxY)
        }
        
        let imageSize = CGSize(width: CGFloat(cgImage.width), height: CGFloat(cgImage.height) + ceil(issuerRect.height) + ceil(labelRect.height) + 4)
        let renderer = UIGraphicsImageRenderer(size: imageSize)
        return renderer.image { (ctx) in
            ctx.cgContext.setFillColor(UIColor.white.cgColor)
            ctx.cgContext.fill(CGRect(origin: .zero, size: imageSize))
            
            issuer.draw(in: issuerRect, withAttributes: [.font: issuerFont, .paragraphStyle: paragraphStyle])
            
            if let label = key.label {
                (label as NSString).draw(in: labelRect, withAttributes: [.font: labelFont, .paragraphStyle: paragraphStyle])
            }
            
            let imageRect = CGRect(x: 0, y: imageSize.height - CGFloat(cgImage.height), width: CGFloat(cgImage.width), height: CGFloat(cgImage.height))
            ctx.cgContext.draw(cgImage, in: imageRect)
        }
    }
    
    var body: some View {
        return mainView
            .navigationTitle("Export QR Code")
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    Button("Done") {
                        dismiss()
                    }
                }
            }
            .background {
                ActivityView(isPresented: $isPresentingShareSheet, items: [image as Any, key.url])
            }
            .task {
                self.image = createImage()
            }
    }
    
    @ViewBuilder
    private var mainView: some View {
        if let image = image {
            VStack(alignment: .center) {
                Image(uiImage: image)
                    .cornerRadius(5)
                    .shadow(radius: 3)
                
                HStack {
                    Button {
                        isPresentingShareSheet = true
                    } label: {
                        Label("Share", systemImage: "square.and.arrow.up")
                    }
                    Spacer()
                    Button(action: save) {
                        Label("Save", systemImage: "square.and.arrow.down")
                    }
                }
            }
            // fix the size so that the HStack doesn't grow beyond with width of the image
            .fixedSize()
        } else {
            ProgressView()
                .progressViewStyle(.circular)
        }
    }
    
    private func save() {
        guard let image = image else { return }
        UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
    }
}

struct ActivityView: UIViewControllerRepresentable {
    var isPresented: Binding<Bool>
    let items: [Any]
    
    func makeUIViewController(context: Context) -> Wrapper {
        return Wrapper(isPresented: isPresented, items: items)
    }
    
    func updateUIViewController(_ uiViewController: Wrapper, context: Context) {
        uiViewController.update(isPresented: isPresented, items: items)
    }
    
    class Wrapper: UIViewController {
        private(set) var isPresented: Binding<Bool>!
        private(set) var items: [Any]!
        
        init(isPresented: Binding<Bool>, items: [Any]) {
            self.isPresented = isPresented
            self.items = items
            
            super.init(nibName: nil, bundle: nil)
        }
        
        required init?(coder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
        
        func update(isPresented: Binding<Bool>, items: [Any]) {
            self.isPresented = isPresented
            self.items = items
            
            if isPresented.wrappedValue, presentedViewController == nil {
                let vc = UIActivityViewController(activityItems: items, applicationActivities: nil)
                vc.completionWithItemsHandler = { (_, _, _, _) in
                    isPresented.wrappedValue = false
                }
                present(vc, animated: true)
            }
        }
    }
}

struct QRCodeView_Previews: PreviewProvider {
    static var previews: some View {
        QRCodeView(key: TOTPKey(urlComponents: URLComponents(string: "otpauth://totp/Example:alice@google.com?secret=JBSWY3DPEHPK3PXP&issuer=Example")!)!)
    }
}