Identify episodes by guid (#5326)

11 files changed, 397 insertions, 93 deletions

diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java b/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java
index dc15b8a9a..49eca1027 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/DBReader.java
@@ -567,15 +567,16 @@ public final class DBReader {
     /**
      * Loads a specific FeedItem from the database.
      *
-     * @param podcastUrl the corresponding feed's url
+     * @param guid feed item guid
      * @param episodeUrl the feed item's url
      * @return The FeedItem or null if the FeedItem could not be found.
      *          Does NOT load additional attributes like feed or queue state.
      */
     @Nullable
-    private static FeedItem getFeedItemByUrl(final String podcastUrl, final String episodeUrl, PodDBAdapter adapter) {
-        Log.d(TAG, "Loading feeditem with podcast url " + podcastUrl + " and episode url " + episodeUrl);
-        try (Cursor cursor = adapter.getFeedItemCursor(podcastUrl, episodeUrl)) {
+    private static FeedItem getFeedItemByGuidOrEpisodeUrl(final String guid, final String episodeUrl,
+            PodDBAdapter adapter) {
+        Log.d(TAG, "Loading feeditem with guid " + guid + " or episode url " + episodeUrl);
+        try (Cursor cursor = adapter.getFeedItemCursor(guid, episodeUrl)) {
             if (!cursor.moveToNext()) {
                 return null;
             }
@@ -626,18 +627,18 @@ public final class DBReader {
     /**
      * Loads a specific FeedItem from the database.
      *
-     * @param podcastUrl the corresponding feed's url
+     * @param guid feed item guid
      * @param episodeUrl the feed item's url
      * @return The FeedItem or null if the FeedItem could not be found.
      *          Does NOT load additional attributes like feed or queue state.
      */
-    public static FeedItem getFeedItemByUrl(final String podcastUrl, final String episodeUrl) {
-        Log.d(TAG, "getFeedItem() called with: " + "podcastUrl = [" + podcastUrl + "], episodeUrl = [" + episodeUrl + "]");
+    public static FeedItem getFeedItemByGuidOrEpisodeUrl(final String guid, final String episodeUrl) {
+        Log.d(TAG, "getFeedItem() called with: " + "guid = [" + guid + "], episodeUrl = [" + episodeUrl + "]");
 
         PodDBAdapter adapter = PodDBAdapter.getInstance();
         adapter.open();
         try {
-            return getFeedItemByUrl(podcastUrl, episodeUrl, adapter);
+            return getFeedItemByGuidOrEpisodeUrl(guid, episodeUrl, adapter);
         } finally {
             adapter.close();
         }
diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java b/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java
index 9e60f4a4d..34ea5e207 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/DBWriter.java
@@ -803,7 +803,7 @@ public class DBWriter {
         return dbExec.submit(() -> {
             PodDBAdapter adapter = PodDBAdapter.getInstance();
             adapter.open();
-            adapter.setFeedItemlist(items);
+            adapter.storeFeedItemlist(items);
             adapter.close();
             EventBus.getDefault().post(FeedItemEvent.updated(items));
         });
diff --git a/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java b/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java
index 21ca1043f..85ce2dc99 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/storage/PodDBAdapter.java
@@ -558,7 +558,7 @@ public class PodDBAdapter {
                 setFeed(feed);
                 if (feed.getItems() != null) {
                     for (FeedItem item : feed.getItems()) {
-                        setFeedItem(item, false);
+                        updateOrInsertFeedItem(item, false);
                     }
                 }
                 if (feed.getPreferences() != null) {
@@ -582,11 +582,11 @@ public class PodDBAdapter {
         db.update(TABLE_NAME_FEEDS, values, KEY_DOWNLOAD_URL + "=?", new String[]{original});
     }
 
-    public void setFeedItemlist(List<FeedItem> items) {
+    public void storeFeedItemlist(List<FeedItem> items) {
         try {
             db.beginTransactionNonExclusive();
             for (FeedItem item : items) {
-                setFeedItem(item, true);
+                updateOrInsertFeedItem(item, true);
             }
             db.setTransactionSuccessful();
         } catch (SQLException e) {
@@ -600,7 +600,7 @@ public class PodDBAdapter {
         long result = 0;
         try {
             db.beginTransactionNonExclusive();
-            result = setFeedItem(item, true);
+            result = updateOrInsertFeedItem(item, true);
             db.setTransactionSuccessful();
         } catch (SQLException e) {
             Log.e(TAG, Log.getStackTraceString(e));
@@ -618,7 +618,7 @@ public class PodDBAdapter {
      *                 false if the method is executed on a list of FeedItems of the same Feed.
      * @return the id of the entry
      */
-    private long setFeedItem(FeedItem item, boolean saveFeed) {
+    private long updateOrInsertFeedItem(FeedItem item, boolean saveFeed) {
         if (item.getId() == 0 && item.getPubDate() == null) {
             Log.e(TAG, "Newly saved item has no pubDate. Using current date as pubDate");
             item.setPubDate(new Date());
@@ -1110,14 +1110,19 @@ public class PodDBAdapter {
         return db.rawQuery(query, null);
     }
 
-    public final Cursor getFeedItemCursor(final String podcastUrl, final String episodeUrl) {
-        String escapedPodcastUrl = DatabaseUtils.sqlEscapeString(podcastUrl);
+    public final Cursor getFeedItemCursor(final String guid, final String episodeUrl) {
         String escapedEpisodeUrl = DatabaseUtils.sqlEscapeString(episodeUrl);
+        String whereClauseCondition = TABLE_NAME_FEED_MEDIA + "." + KEY_DOWNLOAD_URL + "=" + escapedEpisodeUrl;
+
+        if (guid != null) {
+            String escapedGuid = DatabaseUtils.sqlEscapeString(guid);
+            whereClauseCondition = TABLE_NAME_FEED_ITEMS + "." + KEY_ITEM_IDENTIFIER + "=" + escapedGuid;
+        }
+
         final String query = SELECT_FEED_ITEMS_AND_MEDIA
                 + " INNER JOIN " + TABLE_NAME_FEEDS
                 + " ON " + TABLE_NAME_FEED_ITEMS + "." + KEY_FEED + "=" + TABLE_NAME_FEEDS + "." + KEY_ID
-                + " WHERE " + TABLE_NAME_FEED_MEDIA + "." + KEY_DOWNLOAD_URL + "=" + escapedEpisodeUrl
-                + " AND " + TABLE_NAME_FEEDS + "." + KEY_DOWNLOAD_URL + "=" + escapedPodcastUrl;
+                + " WHERE " + whereClauseCondition;
         Log.d(TAG, "SQL: " + query);
         return db.rawQuery(query, null);
     }
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/EpisodeActionFilter.java b/core/src/main/java/de/danoeh/antennapod/core/sync/EpisodeActionFilter.java
new file mode 100644
index 000000000..c74356d98
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/EpisodeActionFilter.java
@@ -0,0 +1,79 @@
+package de.danoeh.antennapod.core.sync;
+
+import android.util.Log;
+
+import androidx.collection.ArrayMap;
+import androidx.core.util.Pair;
+
+import java.util.List;
+import java.util.Map;
+
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+
+public class EpisodeActionFilter {
+
+    public static final String TAG = "EpisodeActionFilter";
+
+    public static Map<Pair<String, String>, EpisodeAction> getRemoteActionsOverridingLocalActions(
+            List<EpisodeAction> remoteActions,
+            List<EpisodeAction> queuedEpisodeActions) {
+        // make sure more recent local actions are not overwritten by older remote actions
+        Map<Pair<String, String>, EpisodeAction> remoteActionsThatOverrideLocalActions = new ArrayMap<>();
+        Map<Pair<String, String>, EpisodeAction> localMostRecentPlayActions =
+                createUniqueLocalMostRecentPlayActions(queuedEpisodeActions);
+        for (EpisodeAction remoteAction : remoteActions) {
+            Log.d(TAG, "Processing remoteAction: " + remoteAction.toString());
+            Pair<String, String> key = new Pair<>(remoteAction.getPodcast(), remoteAction.getEpisode());
+            switch (remoteAction.getAction()) {
+                case NEW:
+                    remoteActionsThatOverrideLocalActions.put(key, remoteAction);
+                    break;
+                case DOWNLOAD:
+                    break;
+                case PLAY:
+                    EpisodeAction localMostRecent = localMostRecentPlayActions.get(key);
+                    if (secondActionOverridesFirstAction(remoteAction, localMostRecent)) {
+                        break;
+                    }
+                    EpisodeAction remoteMostRecentAction = remoteActionsThatOverrideLocalActions.get(key);
+                    if (secondActionOverridesFirstAction(remoteAction, remoteMostRecentAction)) {
+                        break;
+                    }
+                    remoteActionsThatOverrideLocalActions.put(key, remoteAction);
+                    break;
+                case DELETE:
+                    // NEVER EVER call DBWriter.deleteFeedMediaOfItem() here, leads to an infinite loop
+                    break;
+                default:
+                    Log.e(TAG, "Unknown remoteAction: " + remoteAction);
+                    break;
+            }
+        }
+
+        return remoteActionsThatOverrideLocalActions;
+    }
+
+    private static Map<Pair<String, String>, EpisodeAction> createUniqueLocalMostRecentPlayActions(
+            List<EpisodeAction> queuedEpisodeActions) {
+        Map<Pair<String, String>, EpisodeAction> localMostRecentPlayAction;
+        localMostRecentPlayAction = new ArrayMap<>();
+        for (EpisodeAction action : queuedEpisodeActions) {
+            Pair<String, String> key = new Pair<>(action.getPodcast(), action.getEpisode());
+            EpisodeAction mostRecent = localMostRecentPlayAction.get(key);
+            if (mostRecent == null || mostRecent.getTimestamp() == null) {
+                localMostRecentPlayAction.put(key, action);
+            } else if (mostRecent.getTimestamp().before(action.getTimestamp())) {
+                localMostRecentPlayAction.put(key, action);
+            }
+        }
+        return localMostRecentPlayAction;
+    }
+
+    private static boolean secondActionOverridesFirstAction(EpisodeAction firstAction,
+                                                            EpisodeAction secondAction) {
+        return secondAction != null
+                && secondAction.getTimestamp() != null
+                && secondAction.getTimestamp().after(firstAction.getTimestamp());
+    }
+
+}
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java b/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java
new file mode 100644
index 000000000..6d80a6457
--- /dev/null
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/GuidValidator.java
@@ -0,0 +1,10 @@
+package de.danoeh.antennapod.core.sync;
+
+public class GuidValidator {
+
+    public static boolean isValidGuid(String guid) {
+        return guid != null
+                && !guid.trim().isEmpty();
+    }
+}
+
diff --git a/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java b/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java
index 4736a2c33..9803a29db 100644
--- a/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java
+++ b/core/src/main/java/de/danoeh/antennapod/core/sync/SyncService.java
@@ -7,8 +7,8 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
 import android.util.Log;
+
 import androidx.annotation.NonNull;
-import androidx.collection.ArrayMap;
 import androidx.core.app.NotificationCompat;
 import androidx.core.util.Pair;
 import androidx.work.BackoffPolicy;
@@ -19,6 +19,7 @@ import androidx.work.OneTimeWorkRequest;
 import androidx.work.WorkManager;
 import androidx.work.Worker;
 import androidx.work.WorkerParameters;
+
 import de.danoeh.antennapod.core.R;
 import de.danoeh.antennapod.core.event.SyncServiceEvent;
 import de.danoeh.antennapod.model.feed.Feed;
@@ -45,6 +46,7 @@ import de.danoeh.antennapod.net.sync.model.SyncServiceException;
 import de.danoeh.antennapod.net.sync.model.UploadChangesResponse;
 import io.reactivex.Completable;
 import io.reactivex.schedulers.Schedulers;
+
 import org.apache.commons.lang3.StringUtils;
 import org.greenrobot.eventbus.EventBus;
 import org.json.JSONArray;
@@ -112,13 +114,13 @@ public class SyncService extends Worker {
     public static void clearQueue(Context context) {
         executeLockedAsync(() ->
                 context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE).edit()
-                    .putLong(PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0)
-                    .putLong(PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0)
-                    .putLong(PREF_LAST_SYNC_ATTEMPT_TIMESTAMP, 0)
-                    .putString(PREF_QUEUED_EPISODE_ACTIONS, "[]")
-                    .putString(PREF_QUEUED_FEEDS_ADDED, "[]")
-                    .putString(PREF_QUEUED_FEEDS_REMOVED, "[]")
-                    .apply());
+                        .putLong(PREF_LAST_SUBSCRIPTION_SYNC_TIMESTAMP, 0)
+                        .putLong(PREF_LAST_EPISODE_ACTIONS_SYNC_TIMESTAMP, 0)
+                        .putLong(PREF_LAST_SYNC_ATTEMPT_TIMESTAMP, 0)
+                        .putString(PREF_QUEUED_EPISODE_ACTIONS, "[]")
+                        .putString(PREF_QUEUED_FEEDS_ADDED, "[]")
+                        .putString(PREF_QUEUED_FEEDS_REMOVED, "[]")
+                        .apply());
     }
 
     public static void enqueueFeedAdded(Context context, String downloadUrl) {
@@ -258,7 +260,7 @@ public class SyncService extends Worker {
                     lock.unlock();
                 }
             }).subscribeOn(Schedulers.io())
-                .subscribe();
+                    .subscribe();
         }
     }
 
@@ -429,71 +431,31 @@ public class SyncService extends Worker {
             return;
         }
 
-        Map<Pair<String, String>, EpisodeAction> localMostRecentPlayAction = new ArrayMap<>();
-        for (EpisodeAction action : getQueuedEpisodeActions()) {
-            Pair<String, String> key = new Pair<>(action.getPodcast(), action.getEpisode());
-            EpisodeAction mostRecent = localMostRecentPlayAction.get(key);
-            if (mostRecent == null || mostRecent.getTimestamp() == null) {
-                localMostRecentPlayAction.put(key, action);
-            } else if (mostRecent.getTimestamp().before(action.getTimestamp())) {
-                localMostRecentPlayAction.put(key, action);
-            }
-        }
-
-        // make sure more recent local actions are not overwritten by older remote actions
-        Map<Pair<String, String>, EpisodeAction> mostRecentPlayAction = new ArrayMap<>();
-        for (EpisodeAction action : remoteActions) {
-            Log.d(TAG, "Processing action: " + action.toString());
-            switch (action.getAction()) {
-                case NEW:
-                    FeedItem newItem = DBReader.getFeedItemByUrl(action.getPodcast(), action.getEpisode());
-                    if (newItem != null) {
-                        DBWriter.markItemPlayed(newItem, FeedItem.UNPLAYED, true);
-                    } else {
-                        Log.i(TAG, "Unknown feed item: " + action);
-                    }
-                    break;
-                case DOWNLOAD:
-                    break;
-                case PLAY:
-                    Pair<String, String> key = new Pair<>(action.getPodcast(), action.getEpisode());
-                    EpisodeAction localMostRecent = localMostRecentPlayAction.get(key);
-                    if (localMostRecent == null || localMostRecent.getTimestamp() == null
-                            || localMostRecent.getTimestamp().before(action.getTimestamp())) {
-                        EpisodeAction mostRecent = mostRecentPlayAction.get(key);
-                        if (mostRecent == null || mostRecent.getTimestamp() == null) {
-                            mostRecentPlayAction.put(key, action);
-                        } else if (action.getTimestamp() != null
-                                && mostRecent.getTimestamp().before(action.getTimestamp())) {
-                            mostRecentPlayAction.put(key, action);
-                        } else {
-                            Log.d(TAG, "No date information in action, skipping it");
-                        }
-                    }
-                    break;
-                case DELETE:
-                    // NEVER EVER call DBWriter.deleteFeedMediaOfItem() here, leads to an infinite loop
-                    break;
-                default:
-                    Log.e(TAG, "Unknown action: " + action);
-                    break;
-            }
-        }
+        Map<Pair<String, String>, EpisodeAction> playActionsToUpdate = EpisodeActionFilter
+                .getRemoteActionsOverridingLocalActions(remoteActions, getQueuedEpisodeActions());
         LongList queueToBeRemoved = new LongList();
         List<FeedItem> updatedItems = new ArrayList<>();
-        for (EpisodeAction action : mostRecentPlayAction.values()) {
-            FeedItem playItem = DBReader.getFeedItemByUrl(action.getPodcast(), action.getEpisode());
+        for (EpisodeAction action : playActionsToUpdate.values()) {
+            String guid = GuidValidator.isValidGuid(action.getGuid()) ? action.getGuid() : null;
+            FeedItem feedItem = DBReader.getFeedItemByGuidOrEpisodeUrl(guid, action.getEpisode());
+            if (feedItem == null) {
+                Log.i(TAG, "Unknown feed item: " + action);
+                continue;
+            }
+            if (action.getAction() == EpisodeAction.NEW) {
+                DBWriter.markItemPlayed(feedItem, FeedItem.UNPLAYED, true);
+                continue;
+            }
             Log.d(TAG, "Most recent play action: " + action.toString());
-            if (playItem != null) {
-                FeedMedia media = playItem.getMedia();
-                media.setPosition(action.getPosition() * 1000);
-                if (FeedItemUtil.hasAlmostEnded(playItem.getMedia())) {
-                    Log.d(TAG, "Marking as played");
-                    playItem.setPlayed(true);
-                    queueToBeRemoved.add(playItem.getId());
-                }
-                updatedItems.add(playItem);
+            FeedMedia media = feedItem.getMedia();
+            media.setPosition(action.getPosition() * 1000);
+            if (FeedItemUtil.hasAlmostEnded(feedItem.getMedia())) {
+                Log.d(TAG, "Marking as played");
+                feedItem.setPlayed(true);
+                queueToBeRemoved.add(feedItem.getId());
             }
+            updatedItems.add(feedItem);
+
         }
         DBWriter.removeQueueItem(getApplicationContext(), false, queueToBeRemoved.toArray());
         DBReader.loadAdditionalFeedItemListData(updatedItems);
diff --git a/core/src/play/java/de/danoeh/antennapod/core/cast/CastUtils.java b/core/src/play/java/de/danoeh/antennapod/core/cast/CastUtils.java
index e7daf866c..e1f52aa9f 100644
--- a/core/src/play/java/de/danoeh/antennapod/core/cast/CastUtils.java
+++ b/core/src/play/java/de/danoeh/antennapod/core/cast/CastUtils.java
@@ -192,7 +192,7 @@ public class CastUtils {
                 }
             }
             if (result == null) {
-                FeedItem feedItem = DBReader.getFeedItemByUrl(metadata.getString(KEY_FEED_URL),
+                FeedItem feedItem = DBReader.getFeedItemByGuidOrEpisodeUrl(null,
                         metadata.getString(KEY_EPISODE_IDENTIFIER));
                 if (feedItem != null) {
                     result = feedItem.getMedia();
diff --git a/core/src/test/java/de/danoeh/antennapod/core/storage/DbReaderTest.java b/core/src/test/java/de/danoeh/antennapod/core/storage/DbReaderTest.java
index 07d7242aa..c9be06afd 100644
--- a/core/src/test/java/de/danoeh/antennapod/core/storage/DbReaderTest.java
+++ b/core/src/test/java/de/danoeh/antennapod/core/storage/DbReaderTest.java
@@ -218,7 +218,7 @@ public class DbReaderTest {
         }
         PodDBAdapter adapter = PodDBAdapter.getInstance();
         adapter.open();
-        adapter.setFeedItemlist(downloaded);
+        adapter.storeFeedItemlist(downloaded);
         adapter.close();
         return downloaded;
     }
@@ -257,7 +257,7 @@ public class DbReaderTest {
         }
         PodDBAdapter adapter = PodDBAdapter.getInstance();
         adapter.open();
-        adapter.setFeedItemlist(newItems);
+        adapter.storeFeedItemlist(newItems);
         adapter.close();
         return newItems;
     }
@@ -417,4 +417,23 @@ public class DbReaderTest {
         assertTrue(item2.hasChapters());
         assertEquals(item1.getChapters(), item2.getChapters());
     }
+
+    @Test
+    public void testGetItemByEpisodeUrl() {
+        List<Feed> feeds = saveFeedlist(1, 1, true);
+        FeedItem item1 = feeds.get(0).getItems().get(0);
+        FeedItem feedItemByEpisodeUrl = DBReader.getFeedItemByGuidOrEpisodeUrl(null,
+                item1.getMedia().getDownload_url());
+        assertEquals(item1.getItemIdentifier(), feedItemByEpisodeUrl.getItemIdentifier());
+    }
+
+    @Test
+    public void testGetItemByGuid() {
+        List<Feed> feeds = saveFeedlist(1, 1, true);
+        FeedItem item1 = feeds.get(0).getItems().get(0);
+
+        FeedItem feedItemByGuid = DBReader.getFeedItemByGuidOrEpisodeUrl(item1.getItemIdentifier(),
+                item1.getMedia().getDownload_url());
+        assertEquals(item1.getItemIdentifier(), feedItemByGuid.getItemIdentifier());
+    }
 }
diff --git a/core/src/test/java/de/danoeh/antennapod/core/sync/EpisodeActionFilterTest.java b/core/src/test/java/de/danoeh/antennapod/core/sync/EpisodeActionFilterTest.java
new file mode 100644
index 000000000..94695ca95
--- /dev/null
+++ b/core/src/test/java/de/danoeh/antennapod/core/sync/EpisodeActionFilterTest.java
@@ -0,0 +1,187 @@
+package de.danoeh.antennapod.core.sync;
+
+
+import androidx.core.util.Pair;
+
+import junit.framework.TestCase;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.List;
+import java.util.Map;
+
+import de.danoeh.antennapod.net.sync.model.EpisodeAction;
+
+
+public class EpisodeActionFilterTest extends TestCase {
+
+    EpisodeActionFilter episodeActionFilter = new EpisodeActionFilter();
+
+    public void testGetRemoteActionsHappeningAfterLocalActions() throws ParseException {
+        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
+        Date morning = format.parse("2021-01-01 08:00:00");
+        Date lateMorning = format.parse("2021-01-01 09:00:00");
+
+        List<EpisodeAction> episodeActions = new ArrayList<>();
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(10)
+                .build()
+        );
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(lateMorning)
+                .position(20)
+                .build()
+        );
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(5)
+                .build()
+        );
+
+        Date morningFiveMinutesLater = format.parse("2021-01-01 08:05:00");
+        List<EpisodeAction> remoteActions = new ArrayList<>();
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesLater)
+                .position(10)
+                .build()
+        );
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesLater)
+                .position(5)
+                .build()
+        );
+
+        Map<Pair<String, String>, EpisodeAction> uniqueList = episodeActionFilter
+                .getRemoteActionsOverridingLocalActions(remoteActions, episodeActions);
+        assertSame(1, uniqueList.size());
+    }
+
+    public void testGetRemoteActionsHappeningBeforeLocalActions() throws ParseException {
+        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
+        Date morning = format.parse("2021-01-01 08:00:00");
+        Date lateMorning = format.parse("2021-01-01 09:00:00");
+
+        List<EpisodeAction> episodeActions = new ArrayList<>();
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(10)
+                .build()
+        );
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(lateMorning)
+                .position(20)
+                .build()
+        );
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(5)
+                .build()
+        );
+
+        Date morningFiveMinutesEarlier = format.parse("2021-01-01 07:55:00");
+        List<EpisodeAction> remoteActions = new ArrayList<>();
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesEarlier)
+                .position(10)
+                .build()
+        );
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesEarlier)
+                .position(5)
+                .build()
+        );
+
+        Map<Pair<String, String>, EpisodeAction> uniqueList = episodeActionFilter
+                .getRemoteActionsOverridingLocalActions(remoteActions, episodeActions);
+        assertSame(0, uniqueList.size());
+    }
+
+    public void testGetMultipleRemoteActionsHappeningAfterLocalActions() throws ParseException {
+        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
+        Date morning = format.parse("2021-01-01 08:00:00");
+
+        List<EpisodeAction> episodeActions = new ArrayList<>();
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(10)
+                .build()
+        );
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(5)
+                .build()
+        );
+
+        Date morningFiveMinutesLater = format.parse("2021-01-01 08:05:00");
+        List<EpisodeAction> remoteActions = new ArrayList<>();
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesLater)
+                .position(10)
+                .build()
+        );
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesLater)
+                .position(5)
+                .build()
+        );
+
+        Map<Pair<String, String>, EpisodeAction> uniqueList = episodeActionFilter
+                .getRemoteActionsOverridingLocalActions(remoteActions, episodeActions);
+        assertEquals(2, uniqueList.size());
+    }
+
+    public void testGetMultipleRemoteActionsHappeningBeforeLocalActions() throws ParseException {
+        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
+        Date morning = format.parse("2021-01-01 08:00:00");
+
+        List<EpisodeAction> episodeActions = new ArrayList<>();
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(10)
+                .build()
+        );
+        episodeActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morning)
+                .position(5)
+                .build()
+        );
+
+        Date morningFiveMinutesEarlier = format.parse("2021-01-01 07:55:00");
+        List<EpisodeAction> remoteActions = new ArrayList<>();
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.1", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesEarlier)
+                .position(10)
+                .build()
+        );
+        remoteActions.add(new EpisodeAction
+                .Builder("podcast.a", "episode.2", EpisodeAction.Action.PLAY)
+                .timestamp(morningFiveMinutesEarlier)
+                .position(5)
+                .build()
+        );
+
+        Map<Pair<String, String>, EpisodeAction> uniqueList = episodeActionFilter
+                .getRemoteActionsOverridingLocalActions(remoteActions, episodeActions);
+        assertEquals(0, uniqueList.size());
+    }
+}
\ No newline at end of file
diff --git a/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java b/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java
new file mode 100644
index 000000000..356a7f77e
--- /dev/null
+++ b/core/src/test/java/de/danoeh/antennapod/core/sync/GuidValidatorTest.java
@@ -0,0 +1,18 @@
+package de.danoeh.antennapod.core.sync;
+
+import junit.framework.TestCase;
+
+public class GuidValidatorTest extends TestCase {
+
+    public void testIsValidGuid() {
+        assertTrue(GuidValidator.isValidGuid("skfjsdvgsd"));
+    }
+
+    public void testIsInvalidGuid() {
+        assertFalse(GuidValidator.isValidGuid(""));
+        assertFalse(GuidValidator.isValidGuid(" "));
+        assertFalse(GuidValidator.isValidGuid("\n"));
+        assertFalse(GuidValidator.isValidGuid(" \n"));
+        assertFalse(GuidValidator.isValidGuid(null));
+    }
+}
\ No newline at end of file
diff --git a/net/sync/model/src/main/java/de/danoeh/antennapod/net/sync/model/EpisodeAction.java b/net/sync/model/src/main/java/de/danoeh/antennapod/net/sync/model/EpisodeAction.java
index 1aae5c811..cf4744c3e 100644
--- a/net/sync/model/src/main/java/de/danoeh/antennapod/net/sync/model/EpisodeAction.java
+++ b/net/sync/model/src/main/java/de/danoeh/antennapod/net/sync/model/EpisodeAction.java
@@ -25,6 +25,7 @@ public class EpisodeAction {
 
     private final String podcast;
     private final String episode;
+    private final String guid;
     private final Action action;
     private final Date timestamp;
     private final int started;
@@ -34,6 +35,7 @@ public class EpisodeAction {
     private EpisodeAction(Builder builder) {
         this.podcast = builder.podcast;
         this.episode = builder.episode;
+        this.guid = builder.guid;
         this.action = builder.action;
         this.timestamp = builder.timestamp;
         this.started = builder.started;
@@ -72,6 +74,10 @@ public class EpisodeAction {
                 e.printStackTrace();
             }
         }
+        String guid = object.optString("guid", null);
+        if (!TextUtils.isEmpty(guid)) {
+            builder.guid(guid);
+        }
         if (action == EpisodeAction.Action.PLAY) {
             int started = object.optInt("started", -1);
             int position = object.optInt("position", -1);
@@ -94,6 +100,10 @@ public class EpisodeAction {
         return this.episode;
     }
 
+    public String getGuid() {
+        return this.guid;
+    }
+
     public Action getAction() {
         return this.action;
     }
@@ -143,16 +153,21 @@ public class EpisodeAction {
         }
 
         EpisodeAction that = (EpisodeAction) o;
-        return started == that.started && position == that.position && total == that.total && action != that.action
+        return started == that.started
+                && position == that.position
+                && total == that.total
+                && action != that.action
                 && ObjectsCompat.equals(podcast, that.podcast)
                 && ObjectsCompat.equals(episode, that.episode)
-                && ObjectsCompat.equals(timestamp, that.timestamp);
+                && ObjectsCompat.equals(timestamp, that.timestamp)
+                && ObjectsCompat.equals(guid, that.guid);
     }
 
     @Override
     public int hashCode() {
         int result = podcast != null ? podcast.hashCode() : 0;
         result = 31 * result + (episode != null ? episode.hashCode() : 0);
+        result = 31 * result + (guid != null ? guid.hashCode() : 0);
         result = 31 * result + (action != null ? action.hashCode() : 0);
         result = 31 * result + (timestamp != null ? timestamp.hashCode() : 0);
         result = 31 * result + started;
@@ -171,6 +186,7 @@ public class EpisodeAction {
         try {
             obj.putOpt("podcast", this.podcast);
             obj.putOpt("episode", this.episode);
+            obj.putOpt("guid", this.guid);
             obj.put("action", this.getActionString());
             SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss", Locale.US);
             formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
@@ -193,6 +209,7 @@ public class EpisodeAction {
         return "EpisodeAction{"
                 + "podcast='" + podcast + '\''
                 + ", episode='" + episode + '\''
+                + ", guid='" + guid + '\''
                 + ", action=" + action
                 + ", timestamp=" + timestamp
                 + ", started=" + started
@@ -217,6 +234,7 @@ public class EpisodeAction {
         private int started = -1;
         private int position = -1;
         private int total = -1;
+        private String guid;
 
         public Builder(FeedItem item, Action action) {
             this(item.getFeed().getDownload_url(), item.getMedia().getDownload_url(), action);
@@ -233,6 +251,11 @@ public class EpisodeAction {
             return this;
         }
 
+        public Builder guid(String guid) {
+            this.guid = guid;
+            return this;
+        }
+
         public Builder currentTimestamp() {
             return timestamp(new Date());
         }