public class MainActivity extends AppCompatActivity implements View.OnClickListener{

private Button buttonRegister;
private EditText editTextEmail;
private EditText editTextPassword;
private TextView textViewSignin;

private ProgressDialog progressDialog;

private FirebaseAuth firebaseAuth;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    firebaseAuth = FirebaseAuth.getInstance();
    progressDialog = new ProgressDialog(this);

    if(firebaseAuth.getCurrentUser() != null){
        //Profile activity
        finish();
        startActivity(new Intent(getApplicationContext(), ProfileActivity.class));
    }

    buttonRegister = (Button) findViewById(R.id.buttonRegister);
    editTextEmail = (EditText) findViewById(R.id.editTextEmail);
    editTextPassword = (EditText) findViewById(R.id.editTextPassword);
    textViewSignin = (TextView) findViewById((R.id.textViewSignin));

    buttonRegister.setOnClickListener(this);
    textViewSignin.setOnClickListener(this);
}

private void registerUser(){
    String email = editTextEmail.getText().toString().trim();
    String password = editTextPassword.getText().toString().trim();

    if(TextUtils.isEmpty(email)){
        //email is empty
        Toast.makeText(this, "Please enter email", Toast.LENGTH_LONG).show();
        //stopping the function execution further
        return;
    }

    if(TextUtils.isEmpty(password)){
        //email is empty
        Toast.makeText(this, "Please enter password", Toast.LENGTH_LONG).show();
        //stopping the function execution further
        return;
    }

    //if validations are Okay
    //Register User
    progressDialog.setMessage("Registering User...");
    progressDialog.show();

    firebaseAuth.createUserWithEmailAndPassword(email, password)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if(task.isSuccessful()){
                        //user is successfully registered
                       // Toast.makeText(MainActivity.this, "Registered Successfully", Toast.LENGTH_LONG).show();
                        finish();
                        startActivity((new Intent(getApplicationContext(), ProfileActivity.class)));
                    }
                    else{
                        Toast.makeText(MainActivity.this, "Could not register, Please try again!", Toast.LENGTH_LONG).show();
                    }
                    progressDialog.dismiss();
                }
            });
}

@Override
public void onClick(View view) {
    if(view == buttonRegister) {
        registerUser();
    }

    if (view == textViewSignin){
        //open login activity here
        startActivity(new Intent(this,LoginActivity.class));
    }
}
}

public class ProfileActivity extends AppCompatActivity implements View.OnClickListener {


private FirebaseAuth firebaseAuth;
private DatabaseReference databaseReference;

private TextView textViewUserEmail;
private Button buttonLogout, saveUserInformationBtn;
EditText userName, userAddress;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_profile);

    firebaseAuth = FirebaseAuth.getInstance();

    if (firebaseAuth.getCurrentUser() == null) {
        finish();
        startActivity(new Intent(this, LoginActivity.class));
    }

    databaseReference = FirebaseDatabase.getInstance().getReference();

    FirebaseUser user = firebaseAuth.getCurrentUser();

    textViewUserEmail = (TextView) findViewById(R.id.textViewUserEmail);
    saveUserInformationBtn = (Button) findViewById(R.id.userInfoSave);
    userName = (EditText) findViewById(R.id.userName);
    userAddress = (EditText) findViewById(R.id.userAddress);


    textViewUserEmail.setText("Welcome " + user.getEmail());

    buttonLogout = (Button) findViewById(R.id.buttonLogout);

    buttonLogout.setOnClickListener(this);
    saveUserInformationBtn.setOnClickListener(this);
}

private void saveUserInformation(){
    String name = userName.getText().toString().trim();
    String address = userAddress.getText().toString().trim();

    Userinformation userinformation = new Userinformation(name, address);

    FirebaseUser user = firebaseAuth.getCurrentUser();

    databaseReference.child(user.getUid()).setValue(userinformation);

    Toast.makeText(this, "Information Saved...", Toast.LENGTH_LONG). show();
}

@Override
public void onClick(View view) {
    if(view == buttonLogout){
        firebaseAuth.signOut();
        finish();
        startActivity(new Intent(this,LoginActivity.class));
    }

    if (view == saveUserInformationBtn){
        saveUserInformation();
    }
}
}