reduce object instances, skip querying db if we want to keep all messages

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

@@ -122,6 +122,8 @@ class Core {
     private static final long YIELD_DURATION = 200L; // milliseconds
     private static final long MIN_HIDE = 60 * 1000L; // milliseconds
 
+    private static final FlagTerm FLAGGED = new FlagTerm(new Flags(Flags.Flag.FLAGGED), true);
+
     static void processOperations(
             Context context,
             EntityAccount account, EntityFolder folder,
@@ -1050,7 +1052,11 @@ class Core {
             if (keep_time < 0)
                 keep_time = 0;
 
-            Log.i(folder.name + " sync=" + new Date(sync_time) + " keep=" + new Date(keep_time));
+            Date syncDate = new Date(sync_time);
+            if (folder.keep_days == Integer.MAX_VALUE) {
+                Log.i(folder.name + " sync=" + syncDate + " keep=∞");
+            } else {
+                Log.i(folder.name + " sync=" + syncDate + " keep=" + new Date(keep_time));
 
                 // Delete old local messages
                 if (auto_delete) {
@@ -1069,18 +1075,21 @@ class Core {
                     int old = db.message().deleteMessagesBefore(folder.id, keep_time, delete_unseen);
                     Log.i(folder.name + " local old=" + old);
                 }
+            }
 
             // Get list of local uids
             final List<Long> uids = db.message().getUids(folder.id, sync_kept ? null : sync_time);
             Log.i(folder.name + " local count=" + uids.size());
 
             // Reduce list of local uids
-            SearchTerm searchTerm = new ReceivedDateTerm(ComparisonTerm.GE, new Date(sync_time));
+            ReceivedDateTerm receivedDateSyncTerm = new ReceivedDateTerm(ComparisonTerm.GE, syncDate);
+            SearchTerm searchTerm = receivedDateSyncTerm;
             if (sync_unseen)
                 searchTerm = new OrTerm(searchTerm, new FlagTerm(new Flags(Flags.Flag.SEEN), false));
             if (sync_flagged && ifolder.getPermanentFlags().contains(Flags.Flag.FLAGGED))
-                searchTerm = new OrTerm(searchTerm, new FlagTerm(new Flags(Flags.Flag.FLAGGED), true));
+                searchTerm = new OrTerm(searchTerm, FLAGGED);
 
+            // Get messages to sync from remote
             long search = SystemClock.elapsedRealtime();
             Message[] imessages;
             try {
@@ -1088,11 +1097,12 @@ class Core {
             } catch (MessagingException ex) {
                 Log.w(ex.getMessage());
                 // Fallback to date only search
-                imessages = ifolder.search(new ReceivedDateTerm(ComparisonTerm.GE, new Date(sync_time)));
+                imessages = ifolder.search(receivedDateSyncTerm);
             }
             Log.i(folder.name + " remote count=" + imessages.length +
                     " search=" + (SystemClock.elapsedRealtime() - search) + " ms");
 
+            // Prefetch UIDs and FLAGS of messages to sync
             FetchProfile fp = new FetchProfile();
             fp.add(UIDFolder.FetchProfileItem.UID); // To check if message exists
             fp.add(FetchProfile.Item.FLAGS); // To update existing messages
@@ -1113,6 +1123,7 @@ class Core {
                 }
             });
 
+            // remove messages to be synced from local list? so we get the list of messages to keep
             for (int i = 0; i < imessages.length && state.isRunning() && state.isRecoverable(); i++)
                 try {
                     uids.remove(ifolder.getUID(imessages[i]));
@@ -1125,6 +1136,7 @@ class Core {
                 }
 
             if (uids.size() > 0) {
+                // fetch uids of messages to keep
                 // This is done outside of JavaMail to prevent changed notifications
                 if (!ifolder.isOpen())
                     throw new FolderClosedException(ifolder, "UID FETCH");
@@ -1173,7 +1185,7 @@ class Core {
                                         FetchResponse fr = (FetchResponse) response;
                                         UID uid = fr.getItem(UID.class);
                                         if (uid != null)
-                                            uids.remove(uid.uid);
+                                            uids.remove(uid.uid); // remove message from list if on remote
                                     }
                             } else {
                                 for (Response response : responses)