LoginViewController.swift

//
//  Created by Fredric Cliver on 2020/10/13.
//

import UIKit
import Firebase
import GoogleSignIn
import CryptoKit
import AuthenticationServices

class LoginViewController: UIViewController, ASAuthorizationControllerPresentationContextProviding {
  fileprivate var currentNonce: String?
  func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
    return self.view.window!
  }
  @IBAction func touchedSignInWithAppleButton(_ sender: MyAuthorizationAppleIDButton) {
    startSignInWithAppleFlow()
  }
  
  var handle: AuthStateDidChangeListenerHandle?
  @IBOutlet var signInWithGoogleButton: UIButton!
  
  override func viewDidLoad() {
    super.viewDidLoad()
  }
  
  override func viewDidAppear(_ animated: Bool) {
    GIDSignIn.sharedInstance()?.presentingViewController = self
    //    GIDSignIn.sharedInstance().signIn()
    
    handle = Auth.auth().addStateDidChangeListener() { (auth, user) in
      if user != nil {
        print("logged in")
        self.passUserToMainView()
      }
    }
  }
  
  func passUserToMainView() {
    let storyboard = UIStoryboard(name: Constants.viewIDs.MainStoryboard.rawValue, bundle: nil)
    let vc = storyboard.instantiateViewController(withIdentifier: Constants.viewIDs.MainView.rawValue)
    vc.modalPresentationStyle = .fullScreen
    self.present(vc, animated: true)
  }
  
  @IBAction func onClickSignInGoogle(_ sender: UIButton) {
    GIDSignIn.sharedInstance().signIn()
  }
  
  override func viewWillAppear(_ animated: Bool) {
    
  }
  
  deinit {
    if let handle = handle {
      Auth.auth().removeStateDidChangeListener(handle)
    }
  }
}

// MARK: - extension for Apple signing in
extension LoginViewController: ASAuthorizationControllerDelegate {
  
  @objc @available(iOS 13, *)
  func startSignInWithAppleFlow() {
    let nonce = randomNonceString()
    currentNonce = nonce
    let appleIDProvider = ASAuthorizationAppleIDProvider()
    let request = appleIDProvider.createRequest()
    request.requestedScopes = [.fullName, .email]
    request.nonce = sha256(nonce)
    
    let authorizationController = ASAuthorizationController(authorizationRequests: [request])
    authorizationController.delegate = self
    authorizationController.presentationContextProvider = self
    authorizationController.performRequests()
  }
  
  //MARK: - succeeded on signing in with Apple
  func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
    if let appleIDCredential = authorization.credential as? ASAuthorizationAppleIDCredential {
      guard let nonce = currentNonce else {
        fatalError("Invalid state: A login callback was received, but no login request was sent.")
      }
      guard let appleIDToken = appleIDCredential.identityToken else {
        print("Unable to fetch identity token")
        return
      }
      guard let idTokenString = String(data: appleIDToken, encoding: .utf8) else {
        print("Unable to serialize token string from data: \(appleIDToken.debugDescription)")
        return
      }
      // Initialize a Firebase credential.
      let credential = OAuthProvider.credential(withProviderID: "apple.com", idToken: idTokenString, rawNonce: nonce)
      // Sign in with Firebase.
      Auth.auth().signIn(with: credential) { (authResult, error) in
        if (error != nil) {
          // Error. If error.code == .MissingOrInvalidNonce, make sure
          // you're sending the SHA256-hashed nonce as a hex string with
          // your request to Apple.
          //                    print(error!.localizedDescription)
          ToastManager().showToast(message: error!.localizedDescription)
          return
        }
        // User is signed in to Firebase with Apple.
        self.passUserToMainView()
      }
    }
  }
  
  //MARK: - failed on signing in with Apple
  func authorizationController(controller: ASAuthorizationController, didCompleteWithError error: Error) {
    // Handle error.
    print("Sign in with Apple errored: \(error)")
  }
}


// MARK: - Encrypt Functions
extension LoginViewController {
  // Adapted from https://auth0.com/docs/api-auth/tutorials/nonce#generate-a-cryptographically-random-nonce
  private func randomNonceString(length: Int = 32) -> String {
    precondition(length > 0)
    let charset: Array<Character> =
      Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")
    var result = ""
    var remainingLength = length
    
    while remainingLength > 0 {
      let randoms: [UInt8] = (0 ..< 16).map { _ in
        var random: UInt8 = 0
        let errorCode = SecRandomCopyBytes(kSecRandomDefault, 1, &random)
        if errorCode != errSecSuccess {
          fatalError("Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)")
        }
        return random
      }
      
      randoms.forEach { random in
        if remainingLength == 0 {
          return
        }
        if random < charset.count {
          result.append(charset[Int(random)])
          remainingLength -= 1
        }
      }
    }
    return result
  }
  
  @available(iOS 13, *)
  private func sha256(_ input: String) -> String {
    let inputData = Data(input.utf8)
    let hashedData = SHA256.hash(data: inputData)
    let hashString = hashedData.compactMap {
      return String(format: "%02x", $0)
    }.joined()
    
    return hashString
  }
}