public class QuizActivity extends AppCompatActivity {
public static final String EXTRA_SCORE = "extraScore";
private static final long COUNTDOWN_IN_MILLIS = 30000;

private static final String KEY_SCORE = "keyScore";
private static final String KEY_QUESTION_COUNT = "keyQuestionCount";
private static final String KEY_MILLIS_LEFT = "keyMillisLeft";
private static final String KEY_QUESTION_LIST = "keyQuestionList";
private static final String KEY_ANSWERED = "keyAnswered";

private TextView textViewQuestion;
private TextView textViewScore;
private TextView textViewQuestionCount;
private TextView textViewCountDown;
private RadioGroup rbGroup;
private RadioButton rb1;
private RadioButton rb2;
private RadioButton rb3;
private Button buttonConfirmNext;

private ColorStateList textColorDefaultRb;
private ColorStateList textColorDefaultCd;

private CountDownTimer countDownTimer;
private long timeLeftInMillis;

private ArrayList<Question> questionList;
private int questionCounter;
private int questionCountTotal;
private Question currentQuestion;

private int score;
private boolean answered;

private long backPressedTime;

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

    textViewQuestion = findViewById(R.id.text_view_question);
    textViewScore = findViewById(R.id.text_view_score);
    textViewQuestionCount = findViewById(R.id.text_view_question_count);
    textViewCountDown = findViewById(R.id.text_view_countdown);
    rbGroup = findViewById(R.id.radio_group);
    rb1 = findViewById(R.id.radio_button1);
    rb2 = findViewById(R.id.radio_button2);
    rb3 = findViewById(R.id.radio_button3);
    buttonConfirmNext = findViewById(R.id.button_confirm_next);

    textColorDefaultRb = rb1.getTextColors();
    textColorDefaultCd = textViewCountDown.getTextColors();

    if (savedInstanceState == null) {
        QuizDbHelper dbHelper = new QuizDbHelper(this);
        questionList = dbHelper.getAllQuestions();
        questionCountTotal = questionList.size();
        Collections.shuffle(questionList);

        showNextQuestion();
    } else {
        questionList = savedInstanceState.getParcelableArrayList(KEY_QUESTION_LIST);
        score = savedInstanceState.getInt(KEY_SCORE);
        questionCounter = savedInstanceState.getInt(KEY_QUESTION_COUNT);
        questionCountTotal = questionList.size();
        timeLeftInMillis = savedInstanceState.getLong(KEY_MILLIS_LEFT);
        answered = savedInstanceState.getBoolean(KEY_ANSWERED);

        restoreQuestion();
    }

    buttonConfirmNext.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (!answered) {
                if (rb1.isChecked() || rb2.isChecked() || rb3.isChecked()) {
                    checkAnswer();
                } else {
                    Toast.makeText(QuizActivity.this, "Please select an answer", Toast.LENGTH_SHORT).show();
                }
            } else {
                showNextQuestion();
            }
        }
    });
}

private void showNextQuestion() {
    rb1.setTextColor(textColorDefaultRb);
    rb2.setTextColor(textColorDefaultRb);
    rb3.setTextColor(textColorDefaultRb);
    rbGroup.clearCheck();

    if (questionCounter < questionCountTotal) {
        currentQuestion = questionList.get(questionCounter);

        textViewQuestion.setText(currentQuestion.getQuestion());
        rb1.setText(currentQuestion.getOption1());
        rb2.setText(currentQuestion.getOption2());
        rb3.setText(currentQuestion.getOption3());

        questionCounter++;
        textViewQuestionCount.setText("Question: " + questionCounter + "/" + questionCountTotal);
        answered = false;
        buttonConfirmNext.setText("Confirm");

        timeLeftInMillis = COUNTDOWN_IN_MILLIS;
        startCountDown();
    } else {
        finishQuiz();
    }
}

private void restoreQuestion() {
    currentQuestion = questionList.get(questionCounter-1);

    textViewQuestion.setText(currentQuestion.getQuestion());
    rb1.setText(currentQuestion.getOption1());
    rb2.setText(currentQuestion.getOption2());
    rb3.setText(currentQuestion.getOption3());

    textViewScore.setText("Score: " + score);
    textViewQuestionCount.setText("Question: " + questionCounter + "/" + questionCountTotal);

    if (!answered) {
        buttonConfirmNext.setText("Confirm");
        startCountDown();
    } else {
        updateCountDownText();
        showSolution();
    }
}

private void startCountDown() {
    countDownTimer = new CountDownTimer(timeLeftInMillis, 1000) {
        @Override
        public void onTick(long millisUntilFinished) {
            timeLeftInMillis = millisUntilFinished;
            updateCountDownText();
        }

        @Override
        public void onFinish() {
            timeLeftInMillis = 0;
            updateCountDownText();
            checkAnswer();
        }
    }.start();
}

private void updateCountDownText() {
    int minutes = (int) (timeLeftInMillis / 1000) / 60;
    int seconds = (int) (timeLeftInMillis / 1000) % 60;

    String timeFormatted = String.format(Locale.getDefault(), "%02d:%02d", minutes, seconds);

    textViewCountDown.setText(timeFormatted);

    if (timeLeftInMillis < 10000) {
        textViewCountDown.setTextColor(Color.RED);
    } else {
        textViewCountDown.setTextColor(textColorDefaultCd);
    }
}

private void checkAnswer() {
    answered = true;

    countDownTimer.cancel();

    RadioButton rbSelected = findViewById(rbGroup.getCheckedRadioButtonId());
    int answerNr = rbGroup.indexOfChild(rbSelected) + 1;

    if (answerNr == currentQuestion.getAnswerNr()) {
        score++;
        textViewScore.setText("Score: " + score);
    }

    showSolution();
}

private void showSolution() {
    rb1.setTextColor(Color.RED);
    rb2.setTextColor(Color.RED);
    rb3.setTextColor(Color.RED);

    switch (currentQuestion.getAnswerNr()) {
        case 1:
            rb1.setTextColor(Color.GREEN);
            textViewQuestion.setText("Answer 1 is correct");
            break;
        case 2:
            rb2.setTextColor(Color.GREEN);
            textViewQuestion.setText("Answer 2 is correct");
            break;
        case 3:
            rb3.setTextColor(Color.GREEN);
            textViewQuestion.setText("Answer 3 is correct");
            break;
    }

    if (questionCounter < questionCountTotal) {
        buttonConfirmNext.setText("Next");
    } else {
        buttonConfirmNext.setText("Finish");
    }
}

private void finishQuiz() {
    Intent resultIntent = new Intent();
    resultIntent.putExtra(EXTRA_SCORE, score);
    setResult(RESULT_OK, resultIntent);
    finish();
}

@Override
public void onBackPressed() {
    if (backPressedTime + 2000 > System.currentTimeMillis()) {
        finishQuiz();
    } else {
        Toast.makeText(this, "Press back again to finish", Toast.LENGTH_SHORT).show();
    }

    backPressedTime = System.currentTimeMillis();
}

@Override
protected void onDestroy() {
    super.onDestroy();
    if (countDownTimer != null) {
        countDownTimer.cancel();
    }
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt(KEY_SCORE, score);
    outState.putInt(KEY_QUESTION_COUNT, questionCounter);
    outState.putLong(KEY_MILLIS_LEFT, timeLeftInMillis);
    outState.putParcelableArrayList(KEY_QUESTION_LIST, questionList);
    outState.putBoolean(KEY_ANSWERED, answered);
}
}