private static final String TAG = "EmailPassword";

private TextView mStatusTextView;
private TextView mDetailTextView;
private EditText mEmailField;
private EditText mPasswordField;

// [START declare_auth]
private FirebaseAuth mAuth;
// [END declare_auth]

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_emailpassword);

    // Views
    mStatusTextView = findViewById(R.id.status);
    mDetailTextView = findViewById(R.id.detail);
    mEmailField = findViewById(R.id.field_email);
    mPasswordField = findViewById(R.id.field_password);

    // Buttons
    findViewById(R.id.email_sign_in_button).setOnClickListener(this);
    findViewById(R.id.email_create_account_button).setOnClickListener(this);
    findViewById(R.id.sign_out_button).setOnClickListener(this);
    findViewById(R.id.verify_email_button).setOnClickListener(this);

    // [START initialize_auth]
    mAuth = FirebaseAuth.getInstance();
    // [END initialize_auth]
}

// [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);
}
// [END on_start_check_user]

private void createAccount(String email, String password) {
    Log.d(TAG, "createAccount:" + email);
    if (!validateForm()) {
        return;
    }

    showProgressDialog();

    // [START create_user_with_email]
    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(EmailPasswordActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                        updateUI(null);
                    }

                    // [START_EXCLUDE]
                    hideProgressDialog();
                    // [END_EXCLUDE]
                }
            });
    // [END create_user_with_email]
}

private void signIn(String email, String password) {
    Log.d(TAG, "signIn:" + email);
    if (!validateForm()) {
        return;
    }

    showProgressDialog();

    // [START sign_in_with_email]
    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(EmailPasswordActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                        updateUI(null);
                    }

                    // [START_EXCLUDE]
                    if (!task.isSuccessful()) {
                        mStatusTextView.setText(R.string.auth_failed);
                    }
                    hideProgressDialog();
                    // [END_EXCLUDE]
                }
            });
    // [END sign_in_with_email]
}

private void signOut() {
    mAuth.signOut();
    updateUI(null);
}

private void sendEmailVerification() {
    // Disable button
    findViewById(R.id.verify_email_button).setEnabled(false);

    // Send verification email
    // [START send_email_verification]
    final FirebaseUser user = mAuth.getCurrentUser();
    user.sendEmailVerification()
            .addOnCompleteListener(this, new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    // [START_EXCLUDE]
                    // Re-enable button
                    findViewById(R.id.verify_email_button).setEnabled(true);

                    if (task.isSuccessful()) {
                        Toast.makeText(EmailPasswordActivity.this,
                                "Verification email sent to " + user.getEmail(),
                                Toast.LENGTH_SHORT).show();
                    } else {
                        Log.e(TAG, "sendEmailVerification", task.getException());
                        Toast.makeText(EmailPasswordActivity.this,
                                "Failed to send verification email.",
                                Toast.LENGTH_SHORT).show();
                    }
                    // [END_EXCLUDE]
                }
            });
    // [END send_email_verification]
}

private boolean validateForm() {
    boolean valid = true;

    String email = mEmailField.getText().toString();
    if (TextUtils.isEmpty(email)) {
        mEmailField.setError("Required.");
        valid = false;
    } else {
        mEmailField.setError(null);
    }

    String password = mPasswordField.getText().toString();
    if (TextUtils.isEmpty(password)) {
        mPasswordField.setError("Required.");
        valid = false;
    } else {
        mPasswordField.setError(null);
    }

    return valid;
}

private void updateUI(FirebaseUser user) {
    hideProgressDialog();
    if (user != null) {
        mStatusTextView.setText(getString(R.string.emailpassword_status_fmt,
                user.getEmail(), user.isEmailVerified()));
        mDetailTextView.setText(getString(R.string.firebase_status_fmt, user.getUid()));

        findViewById(R.id.email_password_buttons).setVisibility(View.GONE);
        findViewById(R.id.email_password_fields).setVisibility(View.GONE);
        findViewById(R.id.signed_in_buttons).setVisibility(View.VISIBLE);

        findViewById(R.id.verify_email_button).setEnabled(!user.isEmailVerified());
    } else {
        mStatusTextView.setText(R.string.signed_out);
        mDetailTextView.setText(null);

        findViewById(R.id.email_password_buttons).setVisibility(View.VISIBLE);
        findViewById(R.id.email_password_fields).setVisibility(View.VISIBLE);
        findViewById(R.id.signed_in_buttons).setVisibility(View.GONE);
    }
}

@Override
public void onClick(View v) {
    int i = v.getId();
    if (i == R.id.email_create_account_button) {
        createAccount(mEmailField.getText().toString(), mPasswordField.getText().toString());
    } else if (i == R.id.email_sign_in_button) {
        signIn(mEmailField.getText().toString(), mPasswordField.getText().toString());
    } else if (i == R.id.sign_out_button) {
        signOut();
    } else if (i == R.id.verify_email_button) {
        sendEmailVerification();
    }

}