fix: Correct timer behavior and display

This commit addresses issues with the question timer in `QuizScreen`.

Key changes:

- **QuizScreenViewModel:**
    - Initialize `_remainingTimeSeconds` to `0` instead of `-1` to prevent premature timer display.
    - Start timer only if `timerJob` is `null` (not already running) and it's the first question.
    - Set `timerJob` to `null` when it's cancelled (on choice selection, moving to next question, or finishing the quiz).
    - If a question has no time limit (null or <= 0 seconds), set `_remainingTimeSeconds` to `0` and do not start the `timerJob`.
    - When the timer finishes and no choice was selected, set `_selectedChoiceIndex` to `-1` (indicating time ran out) and ensure `timerJob` is nullified.
- **QuizScreen:**
    - Conditionally display the `TimerBar` only if `selectedChoiceIndex` is `null` (no choice made yet) AND `timerState.totalTimeSeconds` is greater than `0` (meaning there's a valid timer for the current question). This prevents showing a timer when a question has no time limit.

ui/quiz/src/main/kotlin/dev/adriankuta/kahootquiz/ui/quiz/QuizScreen.kt

@@ -129,7 +129,7 @@ private fun QuizScreen(
                 }
 
                 // Timer below choices
-                if (uiState.selectedChoiceIndex == null) {
+                if (uiState.selectedChoiceIndex == null && uiState.timerState.totalTimeSeconds > 0) {
                     item {
                         TimerBar(
                             totalSeconds = uiState.timerState.totalTimeSeconds,

ui/quiz/src/main/kotlin/dev/adriankuta/kahootquiz/ui/quiz/QuizScreenViewModel.kt

@@ -12,10 +12,7 @@ import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
-import kotlinx.coroutines.flow.filterIsInstance
-import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.flow
-import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.stateIn
 import kotlinx.coroutines.launch
 import javax.inject.Inject
@@ -34,7 +31,7 @@ class QuizScreenViewModel @Inject constructor(
             initialValue = QuizUiState.Loading,
         )
     private val _selectedChoiceIndex = MutableStateFlow<Int?>(null)
-    private val _remainingTimeSeconds = MutableStateFlow(-1)
+    private val _remainingTimeSeconds = MutableStateFlow(0)
     private val _currentQuestionIndex = MutableStateFlow(0)
     private var timerJob: Job? = null
 
@@ -44,7 +41,7 @@ class QuizScreenViewModel @Inject constructor(
             quiz.collect { quizState ->
                 if (quizState is QuizUiState.Success) {
                     // Start only if timer hasn't been started yet and we are on the first question
-                    if (_remainingTimeSeconds.value == -1 && _currentQuestionIndex.value == 0) {
+                    if (timerJob == null && _currentQuestionIndex.value == 0) {
                         val firstQuestionTime = quizState.quiz.questions.getOrNull(0)?.time?.inWholeSeconds?.toInt()
                         startCountdown(firstQuestionTime)
                     }
@@ -86,6 +83,7 @@ class QuizScreenViewModel @Inject constructor(
 
     fun onChoiceSelected(index: Int) {
         timerJob?.cancel()
+        timerJob = null
         _selectedChoiceIndex.value = index
     }
 
@@ -103,13 +101,19 @@ class QuizScreenViewModel @Inject constructor(
             } else {
                 // Last question reached: stop timer and keep state (could navigate to results in the future)
                 timerJob?.cancel()
+                timerJob = null
+                _remainingTimeSeconds.value = 0
             }
         }
     }
 
     private fun startCountdown(totalSeconds: Int?) {
         timerJob?.cancel()
-        if (totalSeconds == null || totalSeconds <= 0) return
+        if (totalSeconds == null || totalSeconds <= 0) {
+            _remainingTimeSeconds.value = 0
+            timerJob = null
+            return
+        }
         _remainingTimeSeconds.value = totalSeconds
         timerJob = viewModelScope.launch {
             var remaining = totalSeconds
@@ -122,6 +126,7 @@ class QuizScreenViewModel @Inject constructor(
             if (_selectedChoiceIndex.value == null) {
                 _selectedChoiceIndex.value = -1
             }
+            timerJob = null
         }
     }
 }