SignInAppleDemoView.swift

import SwiftUI
import AuthenticationServices

class AppleAuthViewModel:  ObservableObject {
    @Published var shouldShowAlert: Bool = false
    @Published var alertTitle: String = ""
    @Published var alertMessage: String = ""
    
    //get notified when autherization state gets change
    init() {
        print("👂 init addObserver getAuthorizationState")
        NotificationCenter.default.addObserver(self, selector: #selector(getAuthorizationState), name: ASAuthorizationAppleIDProvider.credentialRevokedNotification, object: nil)
    }
    
    //handle the authorization result that returned from the authorization request in Sign In with Apple button
    func performSignIn(result: Result<ASAuthorization, Error>) {
        print("performSignIn", result)
        switch result {
        case .success(let authorization):
            print("✅ authorized")
            guard let credential = authorization.credential as? ASAuthorizationAppleIDCredential else {
                shouldShowAlert = true
                alertTitle = "Error"
                alertMessage = "Something went wrong. Please try again later."
                return
            }
            
            guard let idToken = credential.identityToken
                .flatMap({ String(data: $0, encoding: .utf8) })
            else {
                return
            }
            
            print("identityToken:", idToken)
            print("authorizedScopes:", credential.authorizedScopes)
            print("email:", credential.email ?? "")
            print("user:", credential.user)
            
            saveUserData(name: credential.fullName?.givenName, email: credential.email, userId: credential.user)
        case .failure(let error):
            print("🚫 Prohibited authorization")
            shouldShowAlert = true
            alertTitle = "Error"
            alertMessage = error.localizedDescription
        }
    }
    
    //store the user information in UserDefaults
    func saveUserData(name: String?, email: String?, userId: String?) {
        print("💾 saveUserData", name ?? "", email ?? "", userId ?? "")
        UserDefaults.standard.setValue(name, forKey: "name")
        UserDefaults.standard.setValue(email, forKey: "email")
        UserDefaults.standard.setValue(userId, forKey: "userId")
    }
    
    //store nil for all user information in USerDefaults
    func deleteUserData(){
        print("🗑️ delete user data")
        UserDefaults.standard.setValue(nil, forKey: "name")
        UserDefaults.standard.setValue(nil, forKey: "email")
        UserDefaults.standard.setValue(nil, forKey: "userId")
    }
    
    //this method gets call when the credential revoked notification has been arised in NotificationCenter
    @objc func getAuthorizationState() {
        print("🚦 getAuthorizationState")
        let provider = ASAuthorizationAppleIDProvider()
        if let userId = UserDefaults.standard.value(forKey: "userId") as? String {
            print("userId", userId) // need for sub consequents validations
            provider.getCredentialState(forUserID: userId) { [self] (state, error) in
                switch state {
                case .authorized:
                    // Credential are still valid
                    print("👍 Credential are still valid")
                    break
                case .revoked:
                    //Credential is revoked. It is similar to Logout. Show login screen.
                    print("✋ credential revoked")
                    //self.deleteUserData()
                    break
                case .notFound:
                    //Credential was not found. Show login screen.
                    print("🤷🏼 Credential was not found. Show login screen.")
                    self.deleteUserData()
                    break
                case .transferred:
                    //The app is transfeered from one development team to another development team. You need to login again so show login screen.
                    self.deleteUserData()
                    break
                default:
                    break
                }
            }
        } else {
            print("⚠️ no found keychain data")
        }
    }
}



//https://medium.com/@daljeetseera9668/sign-in-with-apple-using-swiftui-c2cf57943208
//https://developer.apple.com/design/human-interface-guidelines/sign-in-with-apple
struct SignInAppleDemoView: View {
    
    @ObservedObject var authenticationViewModel: AppleAuthViewModel = AppleAuthViewModel()
    
    
    var body: some View {
        
        VStack {
            
            Button("test signi") {
                AppleSignIn.sharedInstance.appleSignIn()
                
            }
            
            //44 19pt or 56 24pt
            SignInWithAppleButton(.signIn) { request in
                request.requestedScopes = [.fullName, .email]
            } onCompletion: { result in
                
                authenticationViewModel.performSignIn(result: result)

            }
            .signInWithAppleButtonStyle(.whiteOutline)
            .frame(height: 44)
            .padding(.horizontal)
            
            //            SignInWithGoogleButton(style: .whiteOutline)
            //                .padding(.horizontal)
            
            Button("check restorePreviousSignIn") {
                authenticationViewModel.getAuthorizationState()
                
            }
            
            
        }
        .onAppear {
            authenticationViewModel.getAuthorizationState()
        }
        .alert(isPresented: $authenticationViewModel.shouldShowAlert, content: {
            Alert(title: Text(authenticationViewModel.alertTitle), message: Text(authenticationViewModel.alertMessage), dismissButton: .default(Text("OK")))
        })
    }
    
    
}

#Preview {
    SignInAppleDemoView()
}