Where in the code is registration performed, and where is the login?

Question

Java

I can't figure out where I can simply log in the user (without updating the data in the database), and where to register and add a new user to the database. That is: if the user is not registered, we register him and offer him to enter a name by adding data to the database, and if he is already in the database, we simply log him in.

// Initialize phone auth callbacks
        // [START phone_auth_callbacks]
        mCallbacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {

            @Override
            public void onVerificationCompleted(PhoneAuthCredential credential) {
                // This callback will be invoked in two situations:
                // 1 - Instant verification. In some cases the phone number can be instantly
                //     verified without needing to send or enter a verification code.
                // 2 - Auto-retrieval. On some devices Google Play services can automatically
                //     detect the incoming verification SMS and perform verification without
                //     user action.
                Log.d(TAG, "onVerificationCompleted:" + credential);
                // [START_EXCLUDE silent]
                mVerificationInProgress = false;
                // [END_EXCLUDE]

                // [START_EXCLUDE silent]
                // Update the UI and attempt sign in with the phone credential
                updateUI(STATE_VERIFY_SUCCESS, credential);
                // [END_EXCLUDE]
                signInWithPhoneAuthCredential(credential);
            }

            @Override
            public void onVerificationFailed(FirebaseException e) {
                // This callback is invoked in an invalid request for verification is made,
                // for instance if the the phone number format is not valid.
                Log.w(TAG, "onVerificationFailed", e);
                // [START_EXCLUDE silent]
                mVerificationInProgress = false;
                // [END_EXCLUDE]

                if (e instanceof FirebaseAuthInvalidCredentialsException) {
                    // Invalid request
                    // [START_EXCLUDE]
                    mPhoneNumberField.setError("Invalid phone number.");
                    // [END_EXCLUDE]
                } else if (e instanceof FirebaseTooManyRequestsException) {
                    // The SMS quota for the project has been exceeded
                    // [START_EXCLUDE]
                    Snackbar.make(findViewById(android.R.id.content), "Quota exceeded.",
                            Snackbar.LENGTH_SHORT).show();
                    // [END_EXCLUDE]
                }

                // Show a message and update the UI
                // [START_EXCLUDE]
                updateUI(STATE_VERIFY_FAILED);
                // [END_EXCLUDE]
            }

            @Override
            public void onCodeSent(@NonNull String verificationId,
                                   @NonNull PhoneAuthProvider.ForceResendingToken token) {
                // The SMS verification code has been sent to the provided phone number, we
                // now need to ask the user to enter the code and then construct a credential
                // by combining the code with a verification ID.
                Log.d(TAG, "onCodeSent:" + verificationId);

                // Save verification ID and resending token so we can use them later
                mVerificationId = verificationId;
                mResendToken = token;

                // [START_EXCLUDE]
                // Update UI
                updateUI(STATE_CODE_SENT);
                // [END_EXCLUDE]
            }
        };
        // [END phone_auth_callbacks]
    }

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

        // [START_EXCLUDE]
        if (mVerificationInProgress && validatePhoneNumber()) {
            startPhoneNumberVerification(phone);
        }
        // [END_EXCLUDE]
    }
    // [END on_start_check_user]

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putBoolean(KEY_VERIFY_IN_PROGRESS, mVerificationInProgress);
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        mVerificationInProgress = savedInstanceState.getBoolean(KEY_VERIFY_IN_PROGRESS);
    }


    private void startPhoneNumberVerification(String phoneNumber) {
        // [START start_phone_auth]
        PhoneAuthProvider.getInstance().verifyPhoneNumber(
                phoneNumber,        // Phone number to verify
                120,                 // Timeout duration
                TimeUnit.SECONDS,   // Unit of timeout
                this,               // Activity (for callback binding)
                mCallbacks);        // OnVerificationStateChangedCallbacks
        // [END start_phone_auth]

        mVerificationInProgress = true;
    }

    private void verifyPhoneNumberWithCode(String verificationId, String code) {
        // [START verify_with_code]
        PhoneAuthCredential credential = PhoneAuthProvider.getCredential(verificationId, code);
        // [END verify_with_code]
        signInWithPhoneAuthCredential(credential);
    }

    // [START resend_verification]
    private void resendVerificationCode(String phoneNumber,
                                        PhoneAuthProvider.ForceResendingToken token) {
        PhoneAuthProvider.getInstance().verifyPhoneNumber(
                phoneNumber,        // Phone number to verify
                180,                 // Timeout duration
                TimeUnit.SECONDS,   // Unit of timeout
                this,               // Activity (for callback binding)
                mCallbacks,         // OnVerificationStateChangedCallbacks
                token);             // ForceResendingToken from callbacks
    }
    // [END resend_verification]

    // [START sign_in_with_phone]
    private void signInWithPhoneAuthCredential(PhoneAuthCredential credential) {
        mAuth.signInWithCredential(credential)
                .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, "signInWithCredential:success");

                            FirebaseUser user = task.getResult().getUser();
                            // [START_EXCLUDE]
                            updateUI(STATE_SIGNIN_SUCCESS, user);
                            // [END_EXCLUDE]
                        } else {
                            // Sign in failed, display a message and update the UI
                            Log.w(TAG, "signInWithCredential:failure", task.getException());
                            if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) {
                                // The verification code entered was invalid
                                // [START_EXCLUDE silent]
                                mVerificationField.setError("Invalid code.");
                                // [END_EXCLUDE]
                            }
                            // [START_EXCLUDE silent]
                            // Update UI
                            updateUI(STATE_SIGNIN_FAILED);
                            // [END_EXCLUDE]
                        }
                    }
                });
    }
    // [END sign_in_with_phone]

Answer 1

The OOP problem is non-obvious behavior, until you expand all the noodles and inherited classes, you don’t understand what and how it works, start with the onStart function
This piece will update some data about the user in the application in two non-obvious cases:
1. if he is already registered, then will show, for example, his profile
2. if not registered, then he will also update something, but it is not known what, for example, nothing

FirebaseUser currentUser = mAuth.getCurrentUser();
updateUI(currentUser);

This piece will be executed only in one case, if the user has not yet passed verification, i.e. currently logging in, waiting for a text message or something else

if (mVerificationInProgress && validatePhoneNumber()) {
    startPhoneNumberVerification(phone);
}

Registration or login will end at this location if the user has just been created or logged in with an existing login. If the user has already logged in before and the application remembers him, then this piece of code will not be reached.

Log.d(TAG, "signInWithCredential:success");
FirebaseUser user = task.getResult().getUser();
// [START_EXCLUDE]
updateUI(STATE_SIGNIN_SUCCESS, user);
// [END_EXCLUDE]