Backup classifier data

app/src/main/java/eu/faircode/email/MessageClassifier.java

@@ -25,6 +25,7 @@ import android.os.Build;
 import android.text.TextUtils;
 import android.util.JsonReader;
 import android.util.JsonWriter;
+import android.util.MalformedJsonException;
 
 import androidx.annotation.NonNull;
 import androidx.preference.PreferenceManager;
@@ -390,6 +391,17 @@ public class MessageClassifier {
         long start = new Date().getTime();
 
         File file = getFile(context);
+        if (file.exists())
+            try {
+                File backup = getBackupFile(context);
+                Log.i("Classifier backup " + backup);
+                backup.delete();
+                file.renameTo(backup);
+            } catch (Throwable ex) {
+                Log.w(ex);
+            }
+
+        Log.i("Classifier save " + file);
         try (JsonWriter writer = new JsonWriter(new BufferedWriter(new FileWriter(file)))) {
             writer.beginObject();
 
@@ -467,9 +479,31 @@ public class MessageClassifier {
             return;
 
         clear(context);
+        File file = getFile(context);
+        try {
+            _load(file);
+        } catch (MalformedJsonException ex) {
+            Log.w(ex);
+            clear(context);
+            File backup = getBackupFile(context);
+            if (backup.exists())
+                try {
+                    _load(backup);
+                } catch (Throwable ex1) {
+                    Log.e(ex1);
+                    backup.delete();
+                    clear(context);
+                }
+        } catch (Throwable ex) {
+            Log.e(ex);
+            file.delete();
+            clear(context);
+        }
+    }
 
+    private static synchronized void _load(File file) throws IOException {
+        Log.i("Classifier read " + file);
         long start = new Date().getTime();
-        File file = getFile(context);
         if (file.exists())
             try (JsonReader reader = new JsonReader(new BufferedReader(new FileReader(file)))) {
                 reader.beginObject();
@@ -599,10 +633,6 @@ public class MessageClassifier {
                             break;
                     }
                 reader.endObject();
-            } catch (Throwable ex) {
-                Log.e(ex);
-                file.delete();
-                clear(context);
             }
 
         loaded = true;
@@ -654,6 +684,10 @@ public class MessageClassifier {
         return new File(context.getFilesDir(), "classifier.json");
     }
 
+    static File getBackupFile(@NonNull Context context) {
+        return new File(context.getFilesDir(), "classifier.backup");
+    }
+
     private static class State {
         private final List<String> words = new ArrayList<>();
         private final Map<String, Stat> classStats = new HashMap<>();