public class MainActivity extends AppCompatActivity {

    private FirebaseAuth mAuth;

    String email = "gg@gmail.com";
    String password = "123456";
    String TAG = "LogTestLogin";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mAuth = FirebaseAuth.getInstance();
        createAccount();
        signIn();
    }

    @Override
    public void onStart() {
        super.onStart();
        // Check if user is signed in (non-null) and update UI accordingly.
        FirebaseUser currentUser = mAuth.getCurrentUser();
        updateUI(currentUser);
    }

    private void createAccount() {
        mAuth.createUserWithEmailAndPassword(email, password)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            Log.d(TAG, "createUserWithEmail:success");
                            FirebaseUser user = mAuth.getCurrentUser();
                            updateUI(user);
                        } else {
                            // If sign in fails, display a message to the user.
                            Log.w(TAG, "createUserWithEmail:failure", task.getException());
                            Toast.makeText(MainActivity.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                            updateUI(null);
                        }

                        // ...
                    }
                });
    }

    private void signIn() {
        mAuth.signInWithEmailAndPassword(email, password)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            // Sign in success, update UI with the signed-in user's information
                            Log.d(TAG, "signInWithEmail:success");
                            FirebaseUser user = mAuth.getCurrentUser();
                            updateUI(user);
                        } else {
                            // If sign in fails, display a message to the user.
                            Log.w(TAG, "signInWithEmail:failure", task.getException());
                            Toast.makeText(MainActivity.this, "Authentication failed.",
                                    Toast.LENGTH_SHORT).show();
                            updateUI(null);
                        }

                        // ...
                    }
                });
    }

    private void updateUI(FirebaseUser user) {
//        FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
        if (user != null) {
            // Name, email address, and profile photo Url
            String name = user.getDisplayName();
            String email = user.getEmail();
            Uri photoUrl = user.getPhotoUrl();

            // Check if user's email is verified
            boolean emailVerified = user.isEmailVerified();

            // 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
            // FirebaseUser.getIdToken() instead.
            String uid = user.getUid();
            String str = "name: " + name +
                    "\nemail: " + email +
                    "\nuid: " + uid +
                    "\nphotoUrl: " + photoUrl;
            Toast.makeText(MainActivity.this, str,
                    Toast.LENGTH_SHORT).show();
        }
    }
}