Merge pull request #659 from hpi-studyu/fix/outdated-cached-subject

Fix/outdated cached subject
hpi-studyu · Jul 24, 2024 · 2dc126f · 2dc126f
2 parents 1fa819c + 3a57727
commit 2dc126f
Show file tree

Hide file tree

Showing 2 changed files with 32 additions and 6 deletions.
diff --git a/app/lib/screens/app_onboarding/loading_screen.dart b/app/lib/screens/app_onboarding/loading_screen.dart
@@ -80,6 +80,8 @@ class _LoadingScreenState extends State<LoadingScreen> {
           subject = await _fetchRemoteSubject(selectedStudyObjectId);
         }
       } catch (exception) {
+        debugPrint(
+            "Could not login and retrieve the study subject: $exception");
         if (exception is SocketException) {
           subject = await Cache.loadSubject();
           StudyULogger.info("Offline mode with cached subject: $subject");

diff --git a/app/lib/util/cache.dart b/app/lib/util/cache.dart
@@ -16,13 +16,37 @@ class Cache {
     assert(subject == (await loadSubject()));
   }
 
-  static Future<StudySubject> loadSubject() async {
+  static Future<StudySubject> loadSubject({StudySubject? backupSubject}) async {
     // debugPrint("Load subject from cache");
     if (await SecureStorage.containsKey(cacheSubjectKey)) {
-      return StudySubject.fromJson(
-        jsonDecode((await SecureStorage.read(cacheSubjectKey))!)
-            as Map<String, dynamic>,
-      );
+      final cachedSubjectStr = await SecureStorage.read(cacheSubjectKey);
+      final cachedSubject =
+          jsonDecode(cachedSubjectStr!) as Map<String, dynamic>;
+      try {
+        return StudySubject.fromJson(cachedSubject);
+      } catch (e) {
+        StudyULogger.warning(
+          "Failed to parse cached subject: $cachedSubjectStr",
+        );
+        if (backupSubject != null) {
+          // Only take progress from cached subject and rest from backup,
+          // as the cached subject might be outdated or corrupted
+
+          // compare IDs to make sure we are not mixing up subjects
+          // If IDs do not match we should not use the cached subject
+          if (backupSubject.id != cachedSubject['id']) {
+            throw Exception(
+              "Cached subject ID does not match remote subject ID",
+            );
+          }
+          final cachedProgress = (cachedSubject['progress'] as List?)
+              ?.map((e) => SubjectProgress.fromJson(e as Map<String, dynamic>))
+              .toList();
+          backupSubject.progress = cachedProgress ?? backupSubject.progress;
+          return backupSubject;
+        }
+        throw Exception("No backup subject provided");
+      }
     } else {
       throw Exception("No cached subject found");
     }
@@ -69,7 +93,7 @@ class Cache {
     if (!(await SecureStorage.containsKey(cacheSubjectKey))) {
       return remoteSubject;
     }
-    final localSubject = await loadSubject();
+    final localSubject = await loadSubject(backupSubject: remoteSubject);
     // local and remote subject are equal, nothing to synchronize
     if (localSubject == remoteSubject) return remoteSubject;
     // remote subject belongs to a different study