// AppDelegate.h
#import <UIKit/UIKit.h>
#import <Google/SignIn.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate, GIDSignInDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

// AppDelegate.m
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  // Override point for customization after application launch.
          
  NSError* configureError;
  [[GGLContext sharedInstance] configureWithError: &configureError];
  NSAssert(!configureError, @"Error configuring Google services: %@", configureError);
                      
  [GIDSignIn sharedInstance].delegate = self;
                              
  return YES;
}

<省略>

- (BOOL)application:(UIApplication *)application openURL:(NSURL *)url sourceApplication:(NSString *)sourceApplication annotation:(id)annotation {
  
  return [[GIDSignIn sharedInstance] handleURL:url sourceApplication:sourceApplication annotation:annotation];
}

// Google Sign-inに成功した場合に呼び出される処理
- (void)signIn:(GIDSignIn *)signIn didSignInForUser:(GIDGoogleUser *)user withError:(NSError *)error {
  // Perform any operations on signed in user here.
  NSString *userId = user.userID;                  // For client-side use only!
  NSString *idToken = user.authentication.idToken; // Safe to send to the server
  NSString *name = user.profile.name;
  NSString *email = user.profile.email;
                      
  NSLog(@"userId: %@, idToken: %@, name: %@, email: %@", userId, idToken, name, email);
}

// Google Sign-inに失敗した場合に呼び出される処理
- (void)signIn:(GIDSignIn *)signIn didDisconnectWithUser:(GIDGoogleUser *)user withError:(NSError *)error {
  // Perform any operations when the user disconnects from app here.
  NSLog(@"error: %@", error);
}

// ViewController.h
#import <UIKit/UIKit.h>
#import <Google/SignIn.h>

@interface ViewController : UIViewController <GIDSignInUIDelegate>

@property (weak, nonatomic) IBOutlet GIDSignInButton *signInButton;

@end

// ViewController.m
- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view, typically from a nib.
          
  [GIDSignIn sharedInstance].uiDelegate = self;
  // 任意のスコープを設定
  [GIDSignIn sharedInstance].scopes = @[@"https://www.googleapis.com/auth/calendar", @"https://www.googleapis.com/auth/drive"];
  NSLog(@"scope: %@", [GIDSignIn sharedInstance].scopes);
}

// エラーが発生した場合に呼び出される処理
- (void)signInWillDispatch:(GIDSignIn *)signIn error:(NSError *)error {
  NSLog(@"error: %@", error);
}

// Google OAuth2認証画面を開始するときに実行される処理
- (void)signIn:(GIDSignIn *)signIn presentViewController:(UIViewController *)viewController {
  // OAuth2認証画面を表示する処理
  [self presentViewController:viewController animated:YES completion:nil];
}

// Google OAuth2認証が完了したら実行される処理
- (void)signIn:(GIDSignIn *)signIn dismissViewController:(UIViewController *)viewController {
  // OAuth2認証の画面を閉じる処理
  [self dismissViewControllerAnimated:YES completion:nil];
}

// Google Sign-inボタンをクリックした場合の処理(Storyboardで設定すること)
- (IBAction)didTapSignIn:(id)sender {
  // Google Sign-inを実行する処理
  [[GIDSignIn sharedInstance] signIn];
}