MainViewController.swift

//
//  Copyright (c) 2016 Google Inc.
//
//  Licensed under the Apache License, Version 2.0 (the "License");
//  you may not use this file except in compliance with the License.
//  You may obtain a copy of the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
//

import AuthenticationServices
import CryptoKit
import GameKit
import UIKit

import FirebaseCore
import Security

// [START usermanagement_view_import]
import FirebaseAuth
// [END usermanagement_view_import]
import GoogleSignIn
import FBSDKCoreKit
import FBSDKLoginKit

private var isMFAEnabled = false

@objc(MainViewController)
// [START signin_controller]
class MainViewController: UITableViewController {
  // [END signin_controller]

  let kSectionMultiFactor = 4
  let kSectionToken = 3
  let kSectionProviders = 2
  let kSectionUser = 1
  let kSectionSignIn = 0

  enum AuthProvider {
    case authEmail
    case authEmailMFA
    case authAnonymous
    case authApple
    case authFacebook
    case authGoogle
    case authTwitter
    case authGitHub
    case authPhone
    case authCustom
    case authPasswordless
    case authGameCenter
    case authMicrosoft
  }

  /*! @var kOKButtonText
       @brief The text of the "OK" button for the Sign In result dialogs.
   */
  let kOKButtonText = "OK"

  /*! @var kTokenRefreshedAlertTitle
       @brief The title of the "Token Refreshed" alert.
   */
  let kTokenRefreshedAlertTitle = "Token"

  /*! @var kTokenRefreshErrorAlertTitle
       @brief The title of the "Token Refresh error" alert.
   */
  let kTokenRefreshErrorAlertTitle = "Get Token Error"

  /** @var kSetDisplayNameTitle
       @brief The title of the "Set Display Name" error dialog.
   */
  let kSetDisplayNameTitle = "Set Display Name"

  /** @var kUnlinkTitle
      @brief The text of the "Unlink from Provider" error Dialog.
   */
  let kUnlinkTitle = "Unlink from Provider"

  /** @var kChangeEmailText
       @brief The title of the "Change Email" button.
   */
  let kChangeEmailText = "Change Email"

  /** @var kChangePasswordText
       @brief The title of the "Change Password" button.
   */
  let kChangePasswordText = "Change Password"

  /** @var kUpdatePhoneNumberText
      @brief The title of the "Update Phone Number" button.
   */
  let kUpdatePhoneNumberText = "Update Phone Number"

  /** @var handle
      @brief The handler for the auth state listener, to allow cancelling later.
   */
  var handle: AuthStateDidChangeListenerHandle?

  /** @var microsoftProvider
      @brief The OAuth provider instance for Microsoft.
   */
  var microsoftProvider: OAuthProvider?

  /** @var twitterProvider
      @brief The OAuth provider instance for Twitter.
   */
  var twitterProvider: OAuthProvider?

  /** @var gitHubProvider
      @brief The OAuth provider instance for GitHub.
   */
  var gitHubProvider: OAuthProvider?

  func showAuthPicker(_ providers: [AuthProvider]) {
    let picker = UIAlertController(title: "Select Provider",
                                   message: nil,
                                   preferredStyle: .alert)
    for provider in providers {
      var action: UIAlertAction
      switch provider {
      case .authEmail:
        action = UIAlertAction(title: "Email", style: .default) { UIAlertAction in
          self.performSegue(withIdentifier: "email", sender: nil)
        }
      case .authEmailMFA:
        action = UIAlertAction(title: "Email with MFA", style: .default) { UIAlertAction in
          isMFAEnabled = true
          self.performSegue(withIdentifier: "email", sender: nil)
        }
      case .authPasswordless:
        action = UIAlertAction(title: "Passwordless", style: .default) { UIAlertAction in
          self.performSegue(withIdentifier: "passwordless", sender: nil)
        }
      case .authCustom:
        action = UIAlertAction(title: "Custom", style: .default) { UIAlertAction in
          self.performSegue(withIdentifier: "customToken", sender: nil)
        }
      case .authAnonymous:
        action = UIAlertAction(title: "Anonymous", style: .default) { UIAlertAction in
          self.showSpinner {
            // [START firebase_auth_anonymous]
            Auth.auth().signInAnonymously { authResult, error in
              // [START_EXCLUDE]
              self.hideSpinner {
                if let error = error {
                  self.showMessagePrompt(error.localizedDescription)
                  return
                }
              }
              // [END_EXCLUDE]
            }
            // [END firebase_auth_anonymous]
          }
        }
      case .authApple:
        if #available(iOS 13, *) {
          action = UIAlertAction(title: "Apple", style: .default) { UIAlertAction in
            self.startSignInWithAppleFlow()
          }
        } else {
          continue
        }
      case .authFacebook:
        action = UIAlertAction(title: "Facebook", style: .default) { UIAlertAction in
          let loginManager = LoginManager()
          loginManager.logIn(permissions: ["email"], from: self, handler: { result, error in
            if let error = error {
              self.showMessagePrompt(error.localizedDescription)
            } else if result!.isCancelled {
              print("FBLogin cancelled")
            } else {
              // [START headless_facebook_auth]
              let credential = FacebookAuthProvider
                .credential(withAccessToken: AccessToken.current!.tokenString)
              // [END headless_facebook_auth]
              self.firebaseLogin(credential)
            }
          })
        }
      case .authGoogle:
        action = UIAlertAction(title: "Google", style: .default) { UIAlertAction in
          self.startSignInWithGoogleFlow()
        }
      case .authTwitter:
        action = UIAlertAction(title: "Twitter", style: .default) { UIAlertAction in
          // [START firebase_auth_twitter]
          self.twitterProvider?.getCredentialWith(_: nil) { credential, error in
            self.showSpinner {
              if let error = error {
                self.hideSpinner {
                  self.showMessagePrompt(error.localizedDescription)
                  return
                }
              }
              if let credential = credential {
                Auth.auth().signIn(with: credential) { result, error in
                  self.hideSpinner {
                    if let error = error {
                      self.showMessagePrompt(error.localizedDescription)
                      return
                    }
                  }
                }
              }
            }
          }
          // [END firebase_auth_twitter]
        }
      case .authGitHub:
        action = UIAlertAction(title: "GitHub", style: .default) { UIAlertAction in
          // [START firebase_auth_github]
          self.gitHubProvider?.getCredentialWith(_: nil) { credential, error in
            self.showSpinner {
              if let error = error {
                self.hideSpinner {
                  self.showMessagePrompt(error.localizedDescription)
                  return
                }
              }
              if let credential = credential {
                Auth.auth().signIn(with: credential) { result, error in
                  self.hideSpinner {
                    if let error = error {
                      self.showMessagePrompt(error.localizedDescription)
                      return
                    }
                  }
                }
              }
            }
          }
          // [END firebase_auth_github]
        }
      case .authPhone:
        action = UIAlertAction(title: "Phone", style: .default) { UIAlertAction in
          self.showTextInputPrompt(withMessage: "Phone Number:") { userPressedOK, userInput in
            if let phoneNumber = userInput {
              self.showSpinner {
                // [START phone_auth]
                PhoneAuthProvider.provider()
                  .verifyPhoneNumber(phoneNumber, uiDelegate: nil) { verificationID, error in
                    // [START_EXCLUDE silent]
                    self.hideSpinner {
                      // [END_EXCLUDE]
                      if let error = error {
                        self.showMessagePrompt(error.localizedDescription)
                        return
                      }
                      // Sign in using the verificationID and the code sent to the user
                      // [START_EXCLUDE]
                      guard let verificationID = verificationID else { return }
                      self
                        .showTextInputPrompt(withMessage: "Verification Code:") { userPressedOK, verificationCode in
                          if let verificationCode = verificationCode {
                            // [START get_phone_cred]
                            let credential = PhoneAuthProvider.provider().credential(
                              withVerificationID: verificationID,
                              verificationCode: verificationCode
                            )
                            // [END get_phone_cred]
                            self.firebaseLogin(credential)
                          } else {
                            self.showMessagePrompt("verification code can't be empty")
                          }
                        }
                    }
                    // [END_EXCLUDE]
                  }
                // [END phone_auth]
              }
            } else {
              self.showMessagePrompt("phone number can't be empty")
            }
          }
        }
      case .authGameCenter:
        action = UIAlertAction(title: "Game Center", style: .default) { UIAlertAction in
          // [START firebase_auth_gamecenter]
          GameCenterAuthProvider.getCredential { credential, error in
            self.showSpinner {
              if let error = error {
                self.hideSpinner {
                  self.showMessagePrompt(error.localizedDescription)
                  return
                }
              }
              if let credential = credential {
                Auth.auth().signIn(with: credential) { result, error in
                  self.hideSpinner {
                    if let error = error {
                      self.showMessagePrompt(error.localizedDescription)
                      return
                    }
                  }
                }
              }
            }
          }
          // [END firebase_auth_gamecenter]
        }
      case .authMicrosoft:
        action = UIAlertAction(title: "Microsoft", style: .default) { UIAlertAction in
          // [START firebase_auth_microsoft]
          self.microsoftProvider?.getCredentialWith(_: nil) { credential, error in
            self.showSpinner {
              if let error = error {
                self.hideSpinner {
                  self.showMessagePrompt(error.localizedDescription)
                  return
                }
              }
              if let credential = credential {
                Auth.auth().signIn(with: credential) { result, error in
                  self.hideSpinner {
                    if let error = error {
                      self.showMessagePrompt(error.localizedDescription)
                      return
                    }
                  }
                }
              }
            }
          }
          // [END firebase_auth_microsoft]
        }
      }
      picker.addAction(action)
    }

    picker.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
    present(picker, animated: true, completion: nil)
  }

  @IBAction func didTapSignIn(_ sender: AnyObject) {
    showAuthPicker([
      AuthProvider.authEmail,
      AuthProvider.authAnonymous,
      AuthProvider.authApple,
      AuthProvider.authGoogle,
      AuthProvider.authFacebook,
      AuthProvider.authTwitter,
      AuthProvider.authGitHub,
      AuthProvider.authPhone,
      AuthProvider.authCustom,
      AuthProvider.authPasswordless,
      AuthProvider.authGameCenter,
      AuthProvider.authMicrosoft,
    ])
  }

  @IBAction func didTapLink(_ sender: AnyObject) {
    var providers = Set([
      AuthProvider.authGoogle,
      AuthProvider.authFacebook,
      AuthProvider.authTwitter,
      AuthProvider.authPhone,
    ])
    // Remove any existing providers. Note that this is not a complete list of
    // providers, so always check the documentation for a complete reference:
    // https://firebase.google.com/docs/auth
    let user = Auth.auth().currentUser
    for info in (user?.providerData)! {
      switch info.providerID {
      case TwitterAuthProviderID:
        providers.remove(AuthProvider.authTwitter)
      case FacebookAuthProviderID:
        providers.remove(AuthProvider.authFacebook)
      case GoogleAuthProviderID:
        providers.remove(AuthProvider.authGoogle)
      case PhoneAuthProviderID:
        providers.remove(AuthProvider.authPhone)
      default:
        break
      }
    }
    showAuthPicker(Array(providers))
  }

  func setTitleDisplay(_ user: User?) {
    if let name = user?.displayName {
      navigationItem.title = "Welcome \(name)"
    } else {
      navigationItem.title = "Authentication Example"
    }
  }

  func firebaseLogin(_ credential: AuthCredential) {
    showSpinner {
      if let user = Auth.auth().currentUser {
        // [START link_credential]
        user.link(with: credential) { authResult, error in
          // [START_EXCLUDE]
          self.hideSpinner {
            if let error = error {
              self.showMessagePrompt(error.localizedDescription)
              return
            }
            self.tableView.reloadData()
          }
          // [END_EXCLUDE]
        }
        // [END link_credential]
      } else {
        // [START signin_credential]
        Auth.auth().signIn(with: credential) { authResult, error in
          // [START_EXCLUDE silent]
          self.hideSpinner {
            // [END_EXCLUDE]
            if let error = error {
              let authError = error as NSError
              if isMFAEnabled, authError.code == AuthErrorCode.secondFactorRequired.rawValue {
                // The user is a multi-factor user. Second factor challenge is required.
                let resolver = authError
                  .userInfo[AuthErrorUserInfoMultiFactorResolverKey] as! MultiFactorResolver
                var displayNameString = ""
                for tmpFactorInfo in resolver.hints {
                  displayNameString += tmpFactorInfo.displayName ?? ""
                  displayNameString += " "
                }
                self.showTextInputPrompt(
                  withMessage: "Select factor to sign in\n\(displayNameString)",
                  completionBlock: { userPressedOK, displayName in
                    var selectedHint: PhoneMultiFactorInfo?
                    for tmpFactorInfo in resolver.hints {
                      if displayName == tmpFactorInfo.displayName {
                        selectedHint = tmpFactorInfo as? PhoneMultiFactorInfo
                      }
                    }
                    PhoneAuthProvider.provider()
                      .verifyPhoneNumber(with: selectedHint!, uiDelegate: nil,
                                         multiFactorSession: resolver
                                           .session) { verificationID, error in
                        if error != nil {
                          print(
                            "Multi factor start sign in failed. Error: \(error.debugDescription)"
                          )
                        } else {
                          self.showTextInputPrompt(
                            withMessage: "Verification code for \(selectedHint?.displayName ?? "")",
                            completionBlock: { userPressedOK, verificationCode in
                              let credential: PhoneAuthCredential? = PhoneAuthProvider.provider()
                                .credential(withVerificationID: verificationID!,
                                            verificationCode: verificationCode!)
                              let assertion: MultiFactorAssertion? = PhoneMultiFactorGenerator
                                .assertion(with: credential!)
                              resolver.resolveSignIn(with: assertion!) { authResult, error in
                                if error != nil {
                                  print(
                                    "Multi factor finanlize sign in failed. Error: \(error.debugDescription)"
                                  )
                                } else {
                                  self.navigationController?.popViewController(animated: true)
                                }
                              }
                            }
                          )
                        }
                      }
                  }
                )
              } else {
                self.showMessagePrompt(error.localizedDescription)
                return
              }
              // [START_EXCLUDE]
              self.showMessagePrompt(error.localizedDescription)
              // [END_EXCLUDE]
              return
            }
            // User is signed in
            // [START_EXCLUDE]
            // Merge prevUser and currentUser accounts and data
            // ...
            // [END_EXCLUDE]
            // [START_EXCLUDE silent]
          }
          // [END_EXCLUDE]
        }
        // [END signin_credential]
      }
    }
  }

  @IBAction func didTapSignOut(_ sender: AnyObject) {
    // [START signout]
    let firebaseAuth = Auth.auth()
    do {
      try firebaseAuth.signOut()
    } catch let signOutError as NSError {
      print("Error signing out: %@", signOutError)
    }
    // [END signout]
  }

  override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    // [START auth_listener]
    handle = Auth.auth().addStateDidChangeListener { auth, user in
      // [START_EXCLUDE]
      self.setTitleDisplay(user)
      self.tableView.reloadData()
      // [END_EXCLUDE]
    }
    // [END auth_listener]
    microsoftProvider = OAuthProvider(providerID: "microsoft.com")
    twitterProvider = OAuthProvider(providerID: "twitter.com")
    gitHubProvider = OAuthProvider(providerID: "github.com")
    // Authenticate Game Center Local Player
    // Uncomment to sign in with Game Center
    // self.authenticateGameCenterLocalPlayer()
  }

  override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    // [START remove_auth_listener]
    Auth.auth().removeStateDidChangeListener(handle!)
    // [END remove_auth_listener]
  }

  func authenticateGameCenterLocalPlayer() {
    let localPlayer = GKLocalPlayer.local
    localPlayer.authenticateHandler = { gcAuthViewController, error in
      if let gcAuthViewController = gcAuthViewController {
        // Pause any activities that require user interaction, then present the
        // gcAuthViewController to the player.
        self.present(gcAuthViewController, animated: true, completion: nil)
      } else if localPlayer.isAuthenticated {
        // Local player is logged in to Game Center.
      } else {
        // Error
        if let error = error {
          self.showMessagePrompt(error.localizedDescription)
          return
        }
      }
    }
  }

  override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    switch section {
    case kSectionSignIn:
      return 1
    case kSectionUser, kSectionToken, kSectionMultiFactor:
      if Auth.auth().currentUser != nil {
        return 1
      } else {
        return 0
      }
    case kSectionProviders:
      if let user = Auth.auth().currentUser {
        return user.providerData.count
      }
      return 0
    default:
      return 0
    }
  }

  override func tableView(_ tableView: UITableView,
                          cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell: UITableViewCell?
    switch indexPath.section {
    case kSectionSignIn:
      // [START current_user]
      if Auth.auth().currentUser != nil {
        // User is signed in.
        // [START_EXCLUDE]
        cell = tableView.dequeueReusableCell(withIdentifier: "SignOut")
        // [END_EXCLUDE]
      } else {
        // No user is signed in.
        // [START_EXCLUDE]
        cell = tableView.dequeueReusableCell(withIdentifier: "SignIn")
        // [END_EXCLUDE]
      }
    // [END current_user]
    case kSectionUser:
      cell = tableView.dequeueReusableCell(withIdentifier: "Profile")
      // [START get_user_profile]
      let user = Auth.auth().currentUser
      // [END get_user_profile]
      // [START user_profile]
      if let user = user {
        // The user's ID, unique to the Firebase project.
        // Do NOT use this value to authenticate with your backend server,
        // if you have one. Use getTokenWithCompletion:completion: instead.
        let uid = user.uid
        let email = user.email
        let photoURL = user.photoURL
        var multiFactorString = "MultiFactor: "
        for info in user.multiFactor.enrolledFactors {
          multiFactorString += info.displayName ?? "[DispayName]"
          multiFactorString += " "
        }
        // [START_EXCLUDE]
        let emailLabel = cell?.viewWithTag(1) as? UILabel
        let userIDLabel = cell?.viewWithTag(2) as? UILabel
        let profileImageView = cell?.viewWithTag(3) as? UIImageView
        let multiFactorLabel = cell?.viewWithTag(4) as? UILabel
        emailLabel?.text = email
        userIDLabel?.text = uid
        multiFactorLabel?.text = multiFactorString
        if isMFAEnabled {
          multiFactorLabel?.isHidden = false
        } else {
          multiFactorLabel?.isHidden = true
        }

        struct last {
          static var photoURL: URL? = nil
        }
        last.photoURL = photoURL // to prevent earlier image overwrites later one.
        if let photoURL = photoURL {
          DispatchQueue.global(qos: .default).async {
            let data = try? Data(contentsOf: photoURL)
            if let data = data {
              let image = UIImage(data: data)
              DispatchQueue.main.async {
                if photoURL == last.photoURL {
                  profileImageView?.image = image
                }
              }
            }
          }
        } else {
          profileImageView?.image = UIImage(named: "ic_account_circle")
        }
        // [END_EXCLUDE]
      }
    // [END user_profile]
    case kSectionProviders:
      cell = tableView.dequeueReusableCell(withIdentifier: "Provider")
      // [START provider_data]
      let userInfo = Auth.auth().currentUser?.providerData[indexPath.row]
      cell?.textLabel?.text = userInfo?.providerID
      // Provider-specific UID
      cell?.detailTextLabel?.text = userInfo?.uid
    // [END provider_data]
    case kSectionToken:
      cell = tableView.dequeueReusableCell(withIdentifier: "Token")
      let requestEmailButton = cell?.viewWithTag(4) as? UIButton
      requestEmailButton?.isEnabled = (Auth.auth().currentUser?.email != nil) ? true : false
    case kSectionMultiFactor:
      cell = tableView.dequeueReusableCell(withIdentifier: "MultiFactor")

    default:
      fatalError("Unknown section in UITableView")
    }
    return cell!
  }

  override func tableView(_ tableView: UITableView,
                          titleForDeleteConfirmationButtonForRowAt indexPath: IndexPath)
    -> String? {
    return "Unlink"
  }

  override func tableView(_ tableView: UITableView,
                          editingStyleForRowAt indexPath: IndexPath) -> UITableViewCell
    .EditingStyle {
    if indexPath.section == kSectionProviders {
      return .delete
    }
    return .none
  }

  // Swipe to delete
  override func tableView(_ tableView: UITableView,
                          commit editingStyle: UITableViewCell.EditingStyle,
                          forRowAt indexPath: IndexPath) {
    if editingStyle == .delete {
      let providerID = Auth.auth().currentUser?.providerData[indexPath.row].providerID
      showSpinner {
        // [START unlink_provider]
        Auth.auth().currentUser?.unlink(fromProvider: providerID!) { user, error in
          // [START_EXCLUDE]
          self.hideSpinner {
            if let error = error {
              self.showMessagePrompt(error.localizedDescription)
              return
            }
            tableView.reloadData()
          }
          // [END_EXCLUDE]
        }
        // [END unlink_provider]
      }
    }
  }

  override func tableView(_ tableView: UITableView,
                          heightForRowAt indexPath: IndexPath) -> CGFloat {
    if indexPath.section == kSectionUser {
      return 200
    }
    return 44
  }

  override func numberOfSections(in tableView: UITableView) -> Int {
    if isMFAEnabled {
      return 5
    } else {
      return 4
    }
  }

  @IBAction func didMultiFactorEnroll(_ sender: Any) {
    let user = Auth.auth().currentUser
    if user == nil {
      print("Please sign in first.")
    } else {
      showTextInputPrompt(withMessage: "Phone Number") { userPressedOK, phoneNumber in
        user?.multiFactor.getSessionWithCompletion { session, error in
          PhoneAuthProvider.provider().verifyPhoneNumber(
            phoneNumber!,
            uiDelegate: nil,
            multiFactorSession: session,
            completion: { verificationID, error in
              if let error = error {
                self.showMessagePrompt(error.localizedDescription)
              } else {
                self.showTextInputPrompt(
                  withMessage: "Verification code",
                  completionBlock: { userPressedOK, verificationCode in
                    let credential = PhoneAuthProvider.provider()
                      .credential(withVerificationID: verificationID!,
                                  verificationCode: verificationCode!)
                    let assertion = PhoneMultiFactorGenerator.assertion(with: credential)
                    self.showTextInputPrompt(
                      withMessage: "Display name",
                      completionBlock: { userPressedOK, displayName in
                        user?.multiFactor.enroll(
                          with: assertion,
                          displayName: displayName,
                          completion: { error in
                            if let error = error {
                              self.showMessagePrompt(error.localizedDescription)
                            } else {
                              print("Multi factor finanlize enroll succeeded.")
                              self.showTypicalUIForUserUpdateResults(
                                withTitle: "Multi Factor",
                                error: error
                              )
                            }
                          }
                        )
                      }
                    )
                  }
                )
              }
            }
          )
        }
      }
    }
  }

  @IBAction func didMultiFactorUnenroll(_ sender: Any) {
    var displayNameString = ""
    for tmpFactorInfo in Auth.auth().currentUser!.multiFactor.enrolledFactors {
      displayNameString += tmpFactorInfo.displayName ?? " "
      displayNameString += " "
    }
    showTextInputPrompt(withMessage: "Multifactor Unenroll \(displayNameString)") { userPressedOK, displayName in
      var factorInfo: MultiFactorInfo?
      for tmpFactorInfo: MultiFactorInfo in Auth.auth().currentUser!.multiFactor.enrolledFactors {
        if displayName == tmpFactorInfo.displayName {
          factorInfo = tmpFactorInfo
        }
      }
      Auth.auth().currentUser?.multiFactor.unenroll(with: factorInfo!, completion: { error in
        if let error = error {
          self.showMessagePrompt(error.localizedDescription)
        } else {
          print("Multi factor finanlize unenroll succeeded.")
          self.showTypicalUIForUserUpdateResults(withTitle: "Multi Factor", error: error)
        }
      })
    }
  }

  @IBAction func didTokenRefresh(_ sender: AnyObject) {
    let action: AuthTokenCallback = { token, error in
      let okAction = UIAlertAction(title: self.kOKButtonText, style: .default) {
        action in print(self.kOKButtonText)
      }
      if let error = error {
        let alertController = UIAlertController(title: self.kTokenRefreshErrorAlertTitle,
                                                message: error.localizedDescription,
                                                preferredStyle: .alert)
        alertController.addAction(okAction)
        self.present(alertController, animated: true, completion: nil)
        return
      }

      // Log token refresh event to Scion.
      Analytics.logEvent("tokenrefresh", parameters: nil)

      let alertController = UIAlertController(title: self.kTokenRefreshedAlertTitle,
                                              message: token, preferredStyle: .alert)
      alertController.addAction(okAction)
      self.present(alertController, animated: true, completion: nil)
    }
    // [START token_refresh]
    Auth.auth().currentUser?.getIDTokenForcingRefresh(true, completion: action)
    // [END token_refresh]
  }

  /** @fn setDisplayName
   @brief Changes the display name of the current user.
   */
  @IBAction func didSetDisplayName(_ sender: AnyObject) {
    showTextInputPrompt(withMessage: "Display Name:") { userPressedOK, userInput in
      if let displayName = userInput {
        self.showSpinner {
          // [START profile_change]
          let changeRequest = Auth.auth().currentUser?.createProfileChangeRequest()
          changeRequest?.displayName = displayName
          changeRequest?.commitChanges { error in
            // [START_EXCLUDE]
            self.hideSpinner {
              self.showTypicalUIForUserUpdateResults(
                withTitle: self.kSetDisplayNameTitle,
                error: error as NSError?
              )
              self.setTitleDisplay(Auth.auth().currentUser)
            }
            // [END_EXCLUDE]
          }
          // [END profile_change]
        }
      } else {
        self.showMessagePrompt("displayname can't be empty")
      }
    }
  }

  /** @fn requestVerifyEmail
   @brief Requests a "verify email" email be sent.
   */
  @IBAction func didRequestVerifyEmail(_ sender: AnyObject) {
    showSpinner {
      // [START send_verification_email]
      Auth.auth().currentUser?.sendEmailVerification { error in
        // [START_EXCLUDE]
        self.hideSpinner {
          if let error = error {
            self.showMessagePrompt(error.localizedDescription)
            return
          }
          self.showMessagePrompt("Sent")
        }
        // [END_EXCLUDE]
      }
      // [END send_verification_email]
    }
  }

  /** @fn changeEmail
   @brief Changes the email address of the current user.
   */
  @IBAction func didChangeEmail(_ sender: AnyObject) {
    showTextInputPrompt(withMessage: "Email Address:") { userPressedOK, userInput in
      if let email = userInput {
        self.showSpinner {
          // [START change_email]
          Auth.auth().currentUser?.updateEmail(to: email) { error in
            // [START_EXCLUDE]
            self.hideSpinner {
              self.showTypicalUIForUserUpdateResults(withTitle: self.kChangeEmailText, error: error)
            }
            // [END_EXCLUDE]
          }
          // [END change_email]
        }
      } else {
        self.showMessagePrompt("email can't be empty")
      }
    }
  }

  /** @fn changePassword
   @brief Changes the password of the current user.
   */
  @IBAction func didChangePassword(_ sender: AnyObject) {
    showTextInputPrompt(withMessage: "New Password:") { userPressedOK, userInput in
      if let password = userInput {
        self.showSpinner {
          // [START change_password]
          Auth.auth().currentUser?.updatePassword(to: password) { error in
            // [START_EXCLUDE]
            self.hideSpinner {
              self.showTypicalUIForUserUpdateResults(
                withTitle: self.kChangePasswordText,
                error: error
              )
            }
            // [END_EXCLUDE]
          }
          // [END change_password]
        }
      } else {
        self.showMessagePrompt("password can't be empty")
      }
    }
  }

  /** @fn updatePhoneNumber
   @brief Updates the phone number of the current user.
   */
  @IBAction func didUpdatePhoneNumber(_ sender: AnyObject) {
    showTextInputPrompt(withMessage: "New Phone Number:") { userPressedOK, userInput in
      if let phoneNumber = userInput {
        self.showSpinner {
          // [START update_phone]
          PhoneAuthProvider.provider()
            .verifyPhoneNumber(phoneNumber, uiDelegate: nil) { verificationID, error in
              // [START_EXCLUDE]
              self.hideSpinner {
                if let error = error {
                  self.showMessagePrompt(error.localizedDescription)
                  return
                }
                guard let verificationID = verificationID else { return }
                self
                  .showTextInputPrompt(withMessage: "Verification Code:") { userPressedOK, userInput in
                    if let verificationCode = userInput {
                      self.showSpinner {
                        // [END_EXCLUDE]
                        let credential = PhoneAuthProvider.provider()
                          .credential(withVerificationID: verificationID,
                                      verificationCode: verificationCode)
                        Auth.auth().currentUser?.updatePhoneNumber(credential) { error in
                          // [END update_phone]
                          self.hideSpinner {
                            self.showTypicalUIForUserUpdateResults(
                              withTitle: self.kUpdatePhoneNumberText,
                              error: error
                            )
                          }
                        }
                      }
                    } else {
                      self.showMessagePrompt("verification code can't be empty")
                    }
                  }
              }
            }
        }
      } else {
        self.showMessagePrompt("phone number can't be empty")
      }
    }
  }

  // MARK: - Helpers

  /** @fn showTypicalUIForUserUpdateResultsWithTitle:error:
   @brief Shows a @c UIAlertView if error is non-nil with the localized description of the error.
   @param resultsTitle The title of the @c UIAlertView
   @param error The error details to display if non-nil.
   */
  func showTypicalUIForUserUpdateResults(withTitle resultsTitle: String, error: Error?) {
    if let error = error {
      let message = "\(error.localizedDescription)"
      let okAction = UIAlertAction(title: kOKButtonText, style: .default) {
        action in print(self.kOKButtonText)
      }
      let alertController = UIAlertController(title: resultsTitle,
                                              message: message, preferredStyle: .alert)
      alertController.addAction(okAction)
      present(alertController, animated: true, completion: nil)
      return
    }
    tableView.reloadData()
  }

  // MARK: - Sign in with Google

  func startSignInWithGoogleFlow() {
    // [START headless_google_auth]
    guard let clientID = FirebaseApp.app()?.options.clientID else { return }

    // Create Google Sign In configuration object.
    let config = GIDConfiguration(clientID: clientID)

    // Start the sign in flow!
    GIDSignIn.sharedInstance.signIn(with: config, presenting: self) { [unowned self] user, error in

      if let error = error {
        // [START_EXCLUDE]
        self.showMessagePrompt(error.localizedDescription)
        // [END_EXCLUDE]
        return
      }

      // [START google_credential]
      guard
        let authentication = user?.authentication,
        let idToken = authentication.idToken
      else {
        return
      }

      let credential = GoogleAuthProvider.credential(withIDToken: idToken,
                                                     accessToken: authentication.accessToken)
      // [END google_credential]

      // [START_EXCLUDE]
      self.firebaseLogin(credential)
      // [END_EXCLUDE]
    }
    // [END headless_google_auth]
  }

  // MARK: - Sign in with Apple

  // Unhashed nonce.
  fileprivate var currentNonce: String?

  @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()
  }

  // [START random_nonce]
  private func randomNonceString(length: Int = 32) -> String {
    precondition(length > 0)
    var randomBytes = [UInt8](repeating: 0, count: length)
    let errorCode = SecRandomCopyBytes(kSecRandomDefault, randomBytes.count, &randomBytes)
    if errorCode != errSecSuccess {
      fatalError(
        "Unable to generate nonce. SecRandomCopyBytes failed with OSStatus \(errorCode)"
      )
    }

    let charset: [Character] =
      Array("0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._")

    let nonce = randomBytes.map { byte in
      // Pick a random character from the set, wrapping around if needed.
      charset[Int(byte) % charset.count]
    }

    return String(nonce)
  }

  // [END random_nonce]

  // [START sha_256]
  @available(iOS 13, *)
  private func sha256(_ input: String) -> String {
    let inputData = Data(input.utf8)
    let hashedData = SHA256.hash(data: inputData)
    let hashString = hashedData.compactMap {
      String(format: "%02x", $0)
    }.joined()

    return hashString
  }

  // [END sha_256]
}

@available(iOS 13.0, *)
extension MainViewController: ASAuthorizationControllerDelegate {
  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.
      firebaseLogin(credential)
    }
  }

  func authorizationController(controller: ASAuthorizationController,
                               didCompleteWithError error: Error) {
    // Handle error.
    print("Sign in with Apple errored: \(error)")
  }
}

@available(iOS 13.0, *)
extension MainViewController: ASAuthorizationControllerPresentationContextProviding {
  func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
    return view.window!
  }
}