public class RegisterActivity extends AppCompatActivity implements GoogleApiClient.OnConnectionFailedListener,
    View.OnClickListener {

private FirebaseAuth mFirebaseAuth;
private ProgressBar progressBar;
private ProgressDialog mProgressDialog;
private GoogleApiClient mGoogleApiClient;
private static final String TAG = "RegisterActivity";

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

    // Get FireBase mFirebaseAuth instance
    mFirebaseAuth = FirebaseAuth.getInstance();

    if (mFirebaseAuth.getCurrentUser() != null) {
        Log.e("45hh", "User logged in already...");
        startActivity(new Intent(RegisterActivity.this, MainActivity.class));
    }


    GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestScopes(new Scope(Scopes.PLUS_LOGIN))
            .requestScopes(new Scope(Scopes.PLUS_ME))
            .requestEmail()
            .build();
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
            .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
            .build();

    final EditText txtEmail = (EditText) findViewById(R.id.txtEmail);
    final EditText txtPassword = (EditText) findViewById(R.id.txtPassword);
    Button btnRegister = (Button) findViewById(R.id.btnRegister);
    Button btnGSignin = (Button) findViewById(R.id.btnGSignin);
    TextView txtAlreadyHaveAccount = (TextView) findViewById(R.id.txtAlreadyHaveAccount);
    progressBar = (ProgressBar) findViewById(R.id.progressBar);

    btnRegister.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String email = txtEmail.getText().toString().trim();
            String password = txtPassword.getText().toString().trim();

            if (TextUtils.isEmpty(email)) {
                Toast.makeText(getApplicationContext(), "Enter email address!", Toast.LENGTH_SHORT).show();
                return;
            } else if (TextUtils.isEmpty(password)) {
                Toast.makeText(getApplicationContext(), "Enter password!", Toast.LENGTH_SHORT).show();
                return;
            }

            if (password.length() < 6) {
                Toast.makeText(getApplicationContext(), "Password too short, enter minimum 6 characters!", Toast.LENGTH_SHORT).show();
                return;
            }

            progressBar.setVisibility(View.VISIBLE);
            // Create user
            mFirebaseAuth.createUserWithEmailAndPassword(email, password)
                    .addOnCompleteListener(RegisterActivity.this, new OnCompleteListener<AuthResult>() {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {
                            if (task.isSuccessful()) {
                                Toast.makeText(RegisterActivity.this, "Successfully registered!", Toast.LENGTH_SHORT).show();
                                progressBar.setVisibility(View.GONE);
                                startActivity(new Intent(RegisterActivity.this, MainActivity.class));
                                finish();
                            } else {
                                Toast.makeText(RegisterActivity.this, "Authentication failed. " + task.getResult(),
                                        Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
        }
    });

    btnGSignin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            signIn();
        }
    });

    txtAlreadyHaveAccount.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            startActivity(new Intent(RegisterActivity.this, LoginActivity.class));
        }
    });
}

private void handleFirebaseAuthResult(AuthResult authResult) {
    if (authResult != null) {
        // Welcome the user
        FirebaseUser user = authResult.getUser();
        Toast.makeText(this, "Welcome " + user.getEmail(), Toast.LENGTH_SHORT).show();

        // Go back to the main activity
        startActivity(new Intent(this, MainActivity.class));
    }
}

private void signIn() {
    Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient);
    startActivityForResult(signInIntent, 9001);
    showProgressDialog();
}

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

    // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
    if (requestCode == 9001) {
        GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data);
        if (result.isSuccess()) {
            // Google Sign In was successful, authenticate with Firebase
            GoogleSignInAccount account = result.getSignInAccount();
            firebaseAuthWithGoogle(account);
        } else {
            if(mProgressDialog!=null){
                hideProgressDialog();
            }
            // Google Sign In failed
            Log.e(TAG, "Google Sign In failed. Status = " + result.getStatus());
        }
    }
}

private void firebaseAuthWithGoogle(GoogleSignInAccount acct) {
    Log.d(TAG, "firebaseAuthWithGooogle:" + acct.getId());
    AuthCredential credential = GoogleAuthProvider.getCredential(acct.getIdToken(), null);
    mFirebaseAuth.signInWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    Log.d(TAG, "signInWithCredential:onComplete:" + task.isSuccessful());

                    // If sign in fails, display a message to the user. If sign in succeeds
                    // the auth state listener will be notified and logic to handle the
                    // signed in user can be handled in the listener.
                    if (!task.isSuccessful()) {
                        Log.w(TAG, "signInWithCredential", task.getException());
                        Toast.makeText(RegisterActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                    } else {
                        Toast.makeText(RegisterActivity.this, "Authentication Success. Please Wait",
                                Toast.LENGTH_SHORT).show();
                        startActivity(new Intent(RegisterActivity.this, MainActivity.class));
                        finish();
                    }
                    hideProgressDialog();
                }
            });
}

public void showProgressDialog() {
    if (mProgressDialog == null) {
        mProgressDialog = new ProgressDialog(this);
        mProgressDialog.setMessage("Loading...");
        mProgressDialog.setIndeterminate(true);
    }

    mProgressDialog.show();
}

public void hideProgressDialog() {
    if (mProgressDialog != null && mProgressDialog.isShowing()) {
        mProgressDialog.dismiss();
    }
}

@Override
public void onClick(View v) {

}

@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    // An unresolvable error has occurred and Google APIs (including Sign-In) will not
    // be available.
    Log.d(TAG, "onConnectionFailed:" + connectionResult);
    Toast.makeText(this, "Google Play Services error.", Toast.LENGTH_SHORT).show();
}
}