no chart

lib/services/deck_storage.dart

@@ -14,17 +14,25 @@ class DeckStorage {
   static const String _deckIdsKey = 'deck_ids';
   bool _initialized = false;
   SharedPreferences? _prefs;
-  final Future<void> _initFuture;
+  Future<void>? _initFuture;
 
-  DeckStorage._internal() : _initFuture = SharedPreferences.getInstance().then((prefs) {
-    _instance._prefs = prefs;
-    _instance._initialized = true;
-  });
+  DeckStorage._internal();
+
+  /// Lazy initialization of SharedPreferences
+  Future<void> _initSharedPreferences() async {
+    if (_initFuture == null) {
+      _initFuture = SharedPreferences.getInstance().then((prefs) {
+        _instance._prefs = prefs;
+        _instance._initialized = true;
+      });
+    }
+    await _initFuture;
+  }
 
   /// Initialize storage with default deck if empty
   Future<void> initialize() async {
     if (_initialized) return;
-    await _initFuture;
+    await _initSharedPreferences();
     
     // Load existing decks
     final deckIds = _prefs!.getStringList(_deckIdsKey) ?? [];
@@ -39,7 +47,7 @@ class DeckStorage {
   /// Ensure storage is initialized
   Future<void> _ensureInitialized() async {
     if (!_initialized) {
-      await _initFuture;
+      await _initSharedPreferences();
       await initialize();
     }
   }
@@ -75,10 +83,10 @@ class DeckStorage {
       'attemptHistory': deck.attemptHistory.map((entry) => {
         'timestamp': entry.timestamp,
         'totalQuestions': entry.totalQuestions,
-        'correctAnswers': entry.correctAnswers,
-        'incorrectAnswers': entry.incorrectAnswers,
-        'skippedAnswers': entry.skippedAnswers,
-        'timeSpentSeconds': entry.timeSpentSeconds,
+        'correctCount': entry.correctCount,
+        'percentageCorrect': entry.percentageCorrect,
+        'timeSpent': entry.timeSpent,
+        'unknownPercentage': entry.unknownPercentage,
       }).toList(),
       'incompleteAttempt': deck.incompleteAttempt != null ? {
         'attemptId': deck.incompleteAttempt!.attemptId,
@@ -145,13 +153,23 @@ class DeckStorage {
     final historyJson = json['attemptHistory'] as List<dynamic>? ?? [];
     final attemptHistory = historyJson.map((entryJson) {
       final entryMap = entryJson as Map<String, dynamic>;
+      // Support both old and new field names for backward compatibility
+      final correctCount = entryMap['correctCount'] as int? ?? 
+                          entryMap['correctAnswers'] as int? ?? 0;
+      final totalQuestions = entryMap['totalQuestions'] as int? ?? 0;
+      final timeSpent = entryMap['timeSpent'] as int? ?? 
+                       (entryMap['timeSpentSeconds'] as int? ?? 0) * 1000; // Convert seconds to milliseconds
+      // Calculate percentageCorrect if not present
+      final percentageCorrect = entryMap['percentageCorrect'] as double? ?? 
+                               (totalQuestions > 0 ? (correctCount / totalQuestions * 100) : 0.0);
+      final unknownPercentage = entryMap['unknownPercentage'] as double? ?? 0.0;
       return AttemptHistoryEntry(
         timestamp: entryMap['timestamp'] as int? ?? 0,
-        totalQuestions: entryMap['totalQuestions'] as int? ?? 0,
-        correctAnswers: entryMap['correctAnswers'] as int? ?? 0,
-        incorrectAnswers: entryMap['incorrectAnswers'] as int? ?? 0,
-        skippedAnswers: entryMap['skippedAnswers'] as int? ?? 0,
-        timeSpentSeconds: entryMap['timeSpentSeconds'] as int?,
+        totalQuestions: totalQuestions,
+        correctCount: correctCount,
+        percentageCorrect: percentageCorrect,
+        timeSpent: timeSpent,
+        unknownPercentage: unknownPercentage,
       );
     }).toList();