/*
 * Copyright 2017 Google
 *
 * 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 <Foundation/Foundation.h>
#import <XCTest/XCTest.h>

#import <FirebaseCore/FIRApp.h>
#import "FirebaseAuth.h"
#import "AuthCredentials.h"

#ifdef NO_NETWORK
#import "ITUIOSTestUtil.h"
#import "ioReplayer/IORManager.h"
#import "ioReplayer/IORTestCase.h"
#endif

#import <GTMSessionFetcher/GTMSessionFetcher.h>
#import <GTMSessionFetcher/GTMSessionFetcherService.h>

/** The user name string for Custom Auth testing account. */
static NSString *const kCustomAuthTestingAccountUserID = KCUSTOM_AUTH_USER_ID;

/** The url for obtaining a valid custom token string used to test Custom Auth. */
static NSString *const kCustomTokenUrl = KCUSTOM_AUTH_TOKEN_URL;

/** The url for obtaining an expired but valid custom token string used to test Custom Auth failure.
 */
static NSString *const kExpiredCustomTokenUrl = KCUSTOM_AUTH_TOKEN_EXPIRED_URL;

/** Facebook app access token that will be used for Facebook Graph API, which is different from
 * account access token.
 */
static NSString *const kFacebookAppAccessToken = KFACEBOOK_APP_ACCESS_TOKEN;

/** Facebook app ID that will be used for Facebook Graph API. */
static NSString *const kFacebookAppID = KFACEBOOK_APP_ID;

static NSString *const kFacebookGraphApiAuthority = @"graph.facebook.com";

static NSString *const kFacebookTestAccountName = KFACEBOOK_USER_NAME;

static NSString *const kGoogleTestAccountName = KGOOGLE_USER_NAME;

/** The invalid custom token string for testing Custom Auth. */
static NSString *const kInvalidCustomToken = @"invalid token.";

/** The testing email address for testCreateAccountWithEmailAndPassword. */
static NSString *const kTestingEmailToCreateUser = @"abc@xyz.com";

/** The testing email address for testSignInExistingUserWithEmailAndPassword. */
static NSString *const kExistingTestingEmailToSignIn = @"456@abc.com";

/** The testing email address for testUpdatingUsersEmail. */
static NSString *const kNewTestingEmail = @"updatedEmail@abc.com";

/** The testing password for testSignInExistingUserWithModifiedEmailAndPassword. */
static NSString *const kNewTestingPasswordToSignIn = @"password_new";

/** Error message for invalid custom token sign in. */
NSString *kInvalidTokenErrorMessage =
    @"The custom token format is incorrect. Please check the documentation.";

NSString *kGoogleCliendId = KGOOGLE_CLIENT_ID;

/** Refresh token of Google test account to exchange for access token. Refresh token never expires
 * unless user revokes it. If this refresh token expires, tests in record mode will fail and this
 * token needs to be updated.
 */
NSString *kGoogleTestAccountRefreshToken = KGOOGLE_TEST_ACCOUNT_REFRESH_TOKEN;

static NSTimeInterval const kExpectationsTimeout = 10;

#ifdef NO_NETWORK
#define SKIP_IF_ON_MOBILE_HARNESS                                                                  \
  if ([ITUIOSTestUtil isOnMobileHarness]) {                                                        \
    NSLog(@"Skipping '%@' on mobile harness", NSStringFromSelector(_cmd));                         \
    return;                                                                                        \
  }
#else
#define SKIP_IF_ON_MOBILE_HARNESS
#endif

#ifdef NO_NETWORK
@interface ApiTests : IORTestCase
#else
@interface ApiTests : XCTestCase
#endif
@end

@implementation ApiTests

/** To reset the app so that each test sees the app in a clean state. */
- (void)setUp {
  [super setUp];
  [self signOut];
}

#pragma mark - Tests

/**
 * This test runs in replay mode by default. To run in a different mode follow the instructions
 * below.
 *
 * Blaze: --test_arg=\'--networkReplayMode=(replay|record|disabled|observe)\'
 *
 * Xcode:
 * Update the following flag in the xcscheme.
 * --networkReplayMode=(replay|record|disabled|observe)
 */
- (void)testCreateAccountWithEmailAndPassword {
  SKIP_IF_ON_MOBILE_HARNESS
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }
  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Created account with email and password."];
  [auth createUserWithEmail:kTestingEmailToCreateUser
                   password:@"password"
                 completion:^(FIRAuthDataResult *result, NSError *error) {
                   if (error) {
                     NSLog(@"createUserWithEmail has error: %@", error);
                   }
                   [expectation fulfill];
                 }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in creating account. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];

  XCTAssertEqualObjects(auth.currentUser.email, kTestingEmailToCreateUser);

  // Clean up the created Firebase user for future runs.
  [self deleteCurrentFirebaseUser];
}

- (void)testUpdatingUsersEmail {
  SKIP_IF_ON_MOBILE_HARNESS
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }

  __block NSError *apiError;
  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Created account with email and password."];
  [auth createUserWithEmail:kTestingEmailToCreateUser
                   password:@"password"
                 completion:^(FIRAuthDataResult *user, NSError *error) {
                   apiError = error;
                   [expectation fulfill];
                 }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout handler:nil];
  expectation = [self expectationWithDescription:@"Created account with email and password."];
  XCTAssertEqualObjects(auth.currentUser.email, kTestingEmailToCreateUser);
  XCTAssertNil(apiError);
  [auth.currentUser updateEmail:kNewTestingEmail
                     completion:^(NSError *_Nullable error) {
    apiError = error;
    [expectation fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout handler:nil];
  XCTAssertNil(apiError);
  XCTAssertEqualObjects(auth.currentUser.email, kNewTestingEmail);
  // Clean up the created Firebase user for future runs.
  [self deleteCurrentFirebaseUser];
}

- (void)testLinkAnonymousAccountToFacebookAccount {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }
  [self signInAnonymously];

  NSDictionary *userInfoDict = [self createFacebookTestingAccount];
  NSString *facebookAccessToken = userInfoDict[@"access_token"];
  NSLog(@"Facebook testing account access token is: %@", facebookAccessToken);
  NSString *facebookAccountId = userInfoDict[@"id"];
  NSLog(@"Facebook testing account id is: %@", facebookAccountId);

  FIRAuthCredential *credential =
      [FIRFacebookAuthProvider credentialWithAccessToken:facebookAccessToken];

  XCTestExpectation *expectation = [self expectationWithDescription:@"Facebook linking finished."];
  [auth.currentUser linkWithCredential:credential
                            completion:^(FIRUser *user, NSError *error) {
                              if (error) {
                                NSLog(@"Link to Facebok error: %@", error);
                              }
                              [expectation fulfill];
                            }];

  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in linking to Facebook. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
  NSArray<id<FIRUserInfo>> *providerData = auth.currentUser.providerData;
  XCTAssertEqual([providerData count], 1);
  XCTAssertEqualObjects([providerData[0] providerID], @"facebook.com");

  // Clean up the created Firebase/Facebook user for future runs.
  [self deleteCurrentFirebaseUser];
  [self deleteFacebookTestingAccountbyId:facebookAccountId];
}

- (void)testSignInAnonymously {
  [self signInAnonymously];
  XCTAssertTrue([FIRAuth auth].currentUser.anonymous);
  [self deleteCurrentFirebaseUser];
}

- (void)testSignInExistingUserWithEmailAndPassword {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }
  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Signed in existing account with email and password."];
  [auth signInWithEmail:kExistingTestingEmailToSignIn
               password:@"password"
             completion:^(FIRAuthDataResult *user, NSError *error) {
               if (error) {
                 NSLog(@"Signing in existing account has error: %@", error);
               }
               [expectation fulfill];
             }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in signing in existing account. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];

  XCTAssertEqualObjects(auth.currentUser.email, kExistingTestingEmailToSignIn);
}

- (void)testSignInWithValidCustomAuthToken {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }

  NSError *error;
  NSString *customToken = [NSString stringWithContentsOfURL:[NSURL URLWithString:kCustomTokenUrl]
                                                   encoding:NSUTF8StringEncoding
                                                      error:&error];
  if (!customToken) {
    XCTFail(@"There was an error retrieving the custom token: %@", error);
  }
  NSLog(@"The valid token is: %@", customToken);

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"CustomAuthToken sign-in finished."];

  [auth signInWithCustomToken:customToken
                   completion:^(FIRAuthDataResult *_Nullable result, NSError *_Nullable error) {
                     if (error) {
                       NSLog(@"Valid token sign in error: %@", error);
                     }
                     [expectation fulfill];
                   }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in CustomAuthToken sign in. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];

  XCTAssertEqualObjects(auth.currentUser.uid, kCustomAuthTestingAccountUserID);
}

- (void)testSignInWithValidCustomAuthExpiredToken {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }

  NSError *error;
  NSString *customToken =
    [NSString stringWithContentsOfURL:[NSURL URLWithString:kExpiredCustomTokenUrl]
                             encoding:NSUTF8StringEncoding
                                error:&error];
  if (!customToken) {
    XCTFail(@"There was an error retrieving the custom token: %@", error);
  }
  XCTestExpectation *expectation =
      [self expectationWithDescription:@"CustomAuthToken sign-in finished."];

  __block NSError *apiError;
  [auth signInWithCustomToken:customToken
                   completion:^(FIRAuthDataResult *_Nullable result, NSError *_Nullable error) {
                     if (error) {
                       apiError = error;
                     }
                     [expectation fulfill];
                   }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in CustomAuthToken sign in. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];

  XCTAssertNil(auth.currentUser);
  XCTAssertEqual(apiError.code, FIRAuthErrorCodeInvalidCustomToken);
}

- (void)testInMemoryUserAfterSignOut {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }
  NSError *error;
  NSString *customToken = [NSString stringWithContentsOfURL:[NSURL URLWithString:kCustomTokenUrl]
                                                   encoding:NSUTF8StringEncoding
                                                      error:&error];
  if (!customToken) {
    XCTFail(@"There was an error retrieving the custom token: %@", error);
  }
  XCTestExpectation *expectation =
      [self expectationWithDescription:@"CustomAuthToken sign-in finished."];
  __block NSError *rpcError;
  [auth signInWithCustomToken:customToken
                   completion:^(FIRAuthDataResult *_Nullable result, NSError *_Nullable error) {
                     if (error) {
                       rpcError = error;
                     }
                     [expectation fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in CustomAuthToken sign in. Error: %@",
                                           error.localizedDescription);
                                 }
  }];
  XCTAssertEqualObjects(auth.currentUser.uid, kCustomAuthTestingAccountUserID);
  XCTAssertNil(rpcError);
  FIRUser *inMemoryUser = auth.currentUser;
  XCTestExpectation *expectation1 = [self expectationWithDescription:@"Profile data change."];
  [auth signOut:NULL];
  rpcError = nil;
  NSString *newEmailAddress = [self fakeRandomEmail];
  XCTAssertNotEqualObjects(newEmailAddress, inMemoryUser.email);
  [inMemoryUser updateEmail:newEmailAddress completion:^(NSError *_Nullable error) {
    rpcError = error;
    [expectation1 fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout handler:nil];
  XCTAssertEqualObjects(inMemoryUser.email, newEmailAddress);
  XCTAssertNil(rpcError);
  XCTAssertNil(auth.currentUser);
}

- (void)testSignInWithInvalidCustomAuthToken {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }
  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Invalid CustomAuthToken sign-in finished."];

  [auth signInWithCustomToken:kInvalidCustomToken
                   completion:^(FIRAuthDataResult *_Nullable result, NSError *_Nullable error) {

                     XCTAssertEqualObjects(error.localizedDescription, kInvalidTokenErrorMessage);
                     [expectation fulfill];
                   }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in CustomAuthToken sign in. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
}

- (void)testSignInWithFaceboook {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }

  NSDictionary *userInfoDict = [self createFacebookTestingAccount];
  NSString *facebookAccessToken = userInfoDict[@"access_token"];
  NSLog(@"Facebook testing account access token is: %@", facebookAccessToken);
  NSString *facebookAccountId = userInfoDict[@"id"];
  NSLog(@"Facebook testing account id is: %@", facebookAccountId);

  FIRAuthCredential *credential =
      [FIRFacebookAuthProvider credentialWithAccessToken:facebookAccessToken];

  XCTestExpectation *expectation = [self expectationWithDescription:@"Facebook sign-in finished."];

  [auth signInWithCredential:credential
                  completion:^(FIRUser *user, NSError *error) {
                    if (error) {
                      NSLog(@"Facebook sign in error: %@", error);
                    }
                    [expectation fulfill];
                  }];

  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in Facebook sign in. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
  XCTAssertEqualObjects(auth.currentUser.displayName, kFacebookTestAccountName);

  // Clean up the created Firebase/Facebook user for future runs.
  [self deleteCurrentFirebaseUser];
  [self deleteFacebookTestingAccountbyId:facebookAccountId];
}

- (void)testSignInWithGoogle {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }
  NSDictionary *userInfoDict = [self getGoogleAccessToken];
  NSString *googleAccessToken = userInfoDict[@"access_token"];
  NSString *googleIdToken = userInfoDict[@"id_token"];
  FIRAuthCredential *credential =
      [FIRGoogleAuthProvider credentialWithIDToken:googleIdToken accessToken:googleAccessToken];

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Signing in with Google finished."];
  [auth signInWithCredential:credential
                  completion:^(FIRUser *user, NSError *error) {
                    if (error) {
                      NSLog(@"Signing in with Google had error: %@", error);
                    }
                    [expectation fulfill];
                  }];

  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in Signing in with Google. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
  XCTAssertEqualObjects(auth.currentUser.displayName, kGoogleTestAccountName);

  // Clean up the created Firebase/Facebook user for future runs.
  [self deleteCurrentFirebaseUser];
}

#pragma mark - Helpers

/** Generate fake random email address */
- (NSString *)fakeRandomEmail {
  NSMutableString *fakeEmail = [[NSMutableString alloc] init];
  for (int i=0; i<10; i++) {
    [fakeEmail appendString:
        [NSString stringWithFormat:@"%c", 'a' + arc4random_uniform('z' - 'a' + 1)]];
  }
  [fakeEmail appendString:@"@gmail.com"];
  return fakeEmail;
}

/** Sign out current account. */
- (void)signOut {
  NSError *signOutError;
  BOOL status = [[FIRAuth auth] signOut:&signOutError];

  // Just log the error because we don't want to fail the test if signing out
  // fails.
  if (!status) {
    NSLog(@"Error signing out: %@", signOutError);
  }
}

/** Creates a Facebook testing account using Facebook Graph API and return a dictionary that
 * constains "id", "access_token", "login_url", "email" and "password" of the created account.
 */
- (NSDictionary *)createFacebookTestingAccount {
  // Build the URL.
  NSString *urltoCreateTestUser =
      [NSString stringWithFormat:@"https://%@/%@/accounts/test-users", kFacebookGraphApiAuthority,
                                 kFacebookAppID];
  // Build the POST request.
  NSString *bodyString =
      [NSString stringWithFormat:@"installed=true&name=%@&permissions=read_stream&access_token=%@",
                                 kFacebookTestAccountName, kFacebookAppAccessToken];
  NSData *postData = [bodyString dataUsingEncoding:NSUTF8StringEncoding];
  GTMSessionFetcherService *service = [[GTMSessionFetcherService alloc] init];
  GTMSessionFetcher *fetcher = [service fetcherWithURLString:urltoCreateTestUser];
  fetcher.bodyData = postData;
  [fetcher setRequestValue:@"text/plain" forHTTPHeaderField:@"Content-Type"];

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Creating Facebook account finished."];
  __block NSData *data = nil;
  [fetcher beginFetchWithCompletionHandler:^(NSData *receivedData, NSError *error) {
    if (error) {
      NSLog(@"Creating Facebook account finished with error: %@", error);
      return;
    }
    data = receivedData;
    [expectation fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in creating Facebook account. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
  NSString *userInfo = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
  NSLog(@"The info of created Facebook testing account is: %@", userInfo);
  // Parses the access token from the JSON data.
  NSDictionary *userInfoDict =
      [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
  return userInfoDict;
}

/** Clean up the created user for tests' future runs. */
- (void)deleteCurrentFirebaseUser {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    NSLog(@"Could not obtain auth object.");
  }

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Delete current user finished."];
  [auth.currentUser deleteWithCompletion:^(NSError *_Nullable error) {
    if (error) {
      XCTFail(@"Failed to delete user. Error: %@.", error);
    }
    [expectation fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in deleting user. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
}

- (void)signInAnonymously {
  FIRAuth *auth = [FIRAuth auth];
  if (!auth) {
    XCTFail(@"Could not obtain auth object.");
  }

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Anonymousy sign-in finished."];
  [auth signInAnonymouslyWithCompletion:^(FIRAuthDataResult *result, NSError *error) {
    if (error) {
      NSLog(@"Anonymousy sign in error: %@", error);
    }
    [expectation fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in anonymousy sign in. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
}

/** Delete a Facebook testing account by account Id using Facebook Graph API. */
- (void)deleteFacebookTestingAccountbyId:(NSString *)accountId {
  // Build the URL.
  NSString *urltoDeleteTestUser =
      [NSString stringWithFormat:@"https://%@/%@", kFacebookGraphApiAuthority, accountId];

  // Build the POST request.
  NSString *bodyString =
      [NSString stringWithFormat:@"method=delete&access_token=%@", kFacebookAppAccessToken];
  NSData *postData = [bodyString dataUsingEncoding:NSUTF8StringEncoding];
  GTMSessionFetcherService *service = [[GTMSessionFetcherService alloc] init];
  GTMSessionFetcher *fetcher = [service fetcherWithURLString:urltoDeleteTestUser];
  fetcher.bodyData = postData;
  [fetcher setRequestValue:@"text/plain" forHTTPHeaderField:@"Content-Type"];

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Deleting Facebook account finished."];
  [fetcher beginFetchWithCompletionHandler:^(NSData *receivedData, NSError *error) {
    NSString *deleteResult =
        [[NSString alloc] initWithData:receivedData encoding:NSUTF8StringEncoding];
    NSLog(@"The result of deleting Facebook account is: %@", deleteResult);
    if (error) {
      NSLog(@"Deleting Facebook account finished with error: %@", error);
    }
    [expectation fulfill];
  }];

  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in deleting Facebook account. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
}

/** Sends http request to Google OAuth2 token server to use refresh token to exchange for Google
 * access token. Returns a dictionary that constains "access_token", "token_type", "expires_in" and
 * "id_token".
 */
- (NSDictionary *)getGoogleAccessToken {
  NSString *googleOauth2TokenServerUrl = @"https://www.googleapis.com/oauth2/v4/token";
  NSString *bodyString =
      [NSString stringWithFormat:@"client_id=%@&grant_type=refresh_token&refresh_token=%@",
                                 kGoogleCliendId, kGoogleTestAccountRefreshToken];
  NSData *postData = [bodyString dataUsingEncoding:NSUTF8StringEncoding];
  GTMSessionFetcherService *service = [[GTMSessionFetcherService alloc] init];
  GTMSessionFetcher *fetcher = [service fetcherWithURLString:googleOauth2TokenServerUrl];
  fetcher.bodyData = postData;
  [fetcher setRequestValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];

  XCTestExpectation *expectation =
      [self expectationWithDescription:@"Exchanging Google account tokens finished."];
  __block NSData *data = nil;
  [fetcher beginFetchWithCompletionHandler:^(NSData *receivedData, NSError *error) {
    if (error) {
      NSLog(@"Exchanging Google account tokens finished with error: %@", error);
      return;
    }
    data = receivedData;
    [expectation fulfill];
  }];
  [self waitForExpectationsWithTimeout:kExpectationsTimeout
                               handler:^(NSError *error) {
                                 if (error != nil) {
                                   XCTFail(@"Failed to wait for expectations "
                                           @"in exchanging Google account tokens. Error: %@",
                                           error.localizedDescription);
                                 }
                               }];
  NSString *userInfo = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
  NSLog(@"The info of exchanged result is: %@", userInfo);
  NSDictionary *userInfoDict =
      [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];
  return userInfoDict;
}
@end