private LoginButton btnLogin;
private CallbackManager callbackManager;
private FirebaseAuth firebaseAuth;
private FirebaseAuth.AuthStateListener firebaseAuthListener;
private UserRegistration userRegistration = new UserRegistration();
private ProgressBar progressBar;
private EditText etName, etLastname, etEmail, etUsername, etPassword;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_option_registration);
    etName = findViewById(R.id.name);
    etLastname = findViewById(R.id.last_name);
    etEmail = findViewById(R.id.email);
    etUsername = findViewById(R.id.username);
    etPassword = findViewById(R.id.password);

    callbackManager = CallbackManager.Factory.create();
    btnLogin = findViewById(R.id.login_button);
    progressBar = findViewById(R.id.progressBar);
    btnLogin.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            AccessToken.getCurrentAccessToken().getPermissions();
            handleFacebookAccessToken(loginResult.getAccessToken());
            //loginResult.getAccessToken().getPermissions();

        }

        @Override
        public void onCancel() {
            Toast.makeText(getApplicationContext(), R.string.cancel_login, Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onError(FacebookException error) {
            Toast.makeText(getApplicationContext(), R.string.error_login, Toast.LENGTH_SHORT).show();
        }
    });

    firebaseAuth = FirebaseAuth.getInstance();
    firebaseAuthListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = firebaseAuth.getCurrentUser();
            if(user != null){
                goFacebookRegisterActivity();
            }
        }
    };
}

private void handleFacebookAccessToken(AccessToken accessToken) {
    AuthCredential credential = FacebookAuthProvider.getCredential(accessToken.getToken());
    firebaseAuth.signInWithCredential(credential).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
        @Override
        public void onComplete(@NonNull Task<AuthResult> task) {
            if(!task.isSuccessful()){
                Toast.makeText(getApplicationContext(), R.string.firebase_error_login, Toast.LENGTH_SHORT).show();
            }

        }
    });
}

private void goFacebookRegisterActivity() {
    Intent intent = new Intent(this, FacebookRegisterActivity.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
    startActivity(intent);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data){
    super.onActivityResult(requestCode, resultCode, data);
    callbackManager.onActivityResult(requestCode, resultCode, data);
}

@Override
protected void onStart() {
    super.onStart();
    firebaseAuth.addAuthStateListener(firebaseAuthListener);
}

@Override
protected void onStop() {
    super.onStop();
    firebaseAuth.removeAuthStateListener(firebaseAuthListener);
}