Rework undo deletion logic.

Previously the MessageFacade and MessageStateHolder both had their own
state of the last deleted message, which was redundant. Now only
MessageStateHolder governs the state of a pending deletion and
MessageFacade handles commiting the deletion to the server.

app/src/main/java/com/github/gotify/messages/MessagesActivity.java

@@ -55,10 +55,10 @@ import com.github.gotify.log.Log;
 import com.github.gotify.log.LogsActivity;
 import com.github.gotify.login.LoginActivity;
 import com.github.gotify.messages.provider.ApplicationHolder;
+import com.github.gotify.messages.provider.MessageDeletion;
 import com.github.gotify.messages.provider.MessageFacade;
 import com.github.gotify.messages.provider.MessageState;
 import com.github.gotify.messages.provider.MessageWithImage;
-import com.github.gotify.messages.provider.PositionPair;
 import com.github.gotify.service.WebSocketService;
 import com.google.android.material.navigation.NavigationView;
 import com.google.android.material.snackbar.BaseTransientBottomBar;
@@ -374,15 +374,15 @@ public class MessagesActivity extends AppCompatActivity
     }
 
     private void undoDelete() {
-        PositionPair positionPair = messages.undoDeleteLocal();
+        MessageDeletion deletion = messages.undoDeleteLocal();
 
-        if (positionPair != null) {
+        if (deletion != null) {
             ListMessageAdapter adapter = (ListMessageAdapter) messagesView.getAdapter();
             adapter.setItems(messages.get(appId));
             int insertPosition =
                     appId == MessageState.ALL_MESSAGES
-                            ? positionPair.getAllPosition()
+                            ? deletion.getAllPosition()
-                            : positionPair.getAppPosition();
+                            : deletion.getAppPosition();
             adapter.notifyItemInserted(insertPosition);
         }
     }

app/src/main/java/com/github/gotify/messages/provider/MessageDeletion.java

@@ -1,10 +1,14 @@
 package com.github.gotify.messages.provider;
 
-public final class PositionPair {
+import com.github.gotify.client.model.Message;
+
+public final class MessageDeletion {
+    private final Message message;
     private final int allPosition;
     private final int appPosition;
 
-    public PositionPair(int allPosition, int appPosition) {
+    public MessageDeletion(Message message, int allPosition, int appPosition) {
+        this.message = message;
         this.allPosition = allPosition;
         this.appPosition = appPosition;
     }
@@ -16,4 +20,8 @@ public final class PositionPair {
     public int getAppPosition() {
         return appPosition;
     }
+
+    public Message getMessage() {
+        return message;
+    }
 }

app/src/main/java/com/github/gotify/messages/provider/MessageFacade.java

@@ -10,7 +10,6 @@ public class MessageFacade {
     private final MessageRequester requester;
     private final MessageStateHolder state;
     private final MessageImageCombiner combiner;
-    private Message messagePendingDeletion;
 
     public MessageFacade(MessageApi api, ApplicationHolder applicationHolder) {
         this.applicationHolder = applicationHolder;
@@ -34,13 +33,6 @@ public class MessageFacade {
         if (state.hasNext || !state.loaded) {
             PagedMessages pagedMessages = requester.loadMore(state);
             this.state.newMessages(appId, pagedMessages);
-
-            // If there is a message with pending removal, it should not reappear in the list when
-            // reloading. Thus, it needs to be removed from the local list again after loading new
-            // messages.
-            if (messagePendingDeletion != null) {
-                this.state.removeMessage(messagePendingDeletion);
-            }
         }
         return get(appId);
     }
@@ -61,23 +53,21 @@ public class MessageFacade {
     }
 
     public synchronized void deleteLocal(Message message) {
-        this.state.removeMessage(message);
         // If there is already a deletion pending, that one should be executed before scheduling the
         // next deletion.
-        if (messagePendingDeletion != null) {
+        if (this.state.deletionPending()) commitDelete();
-            commitDelete();
+        this.state.deleteMessage(message);
-        }
-        messagePendingDeletion = message;
     }
 
     public synchronized void commitDelete() {
-        this.requester.asyncRemoveMessage(messagePendingDeletion);
+        if (this.state.deletionPending()) {
-        messagePendingDeletion = null;
+            MessageDeletion deletion = this.state.purgePendingDeletion();
+            this.requester.asyncRemoveMessage(deletion.getMessage());
+        }
     }
 
-    public synchronized PositionPair undoDeleteLocal() {
+    public synchronized MessageDeletion undoDeleteLocal() {
-        messagePendingDeletion = null;
+        return this.state.undoPendingDeletion();
-        return this.state.undoLastRemoveMessage();
     }
 
     public boolean deleteAll(Integer appId) {

app/src/main/java/com/github/gotify/messages/provider/MessageStateHolder.java

@@ -9,9 +9,7 @@ class MessageStateHolder {
     private int lastReceivedMessage = -1;
     private Map<Integer, MessageState> states = new HashMap<>();
 
-    private Message lastRemovedMessage;
+    private MessageDeletion pendingDeletion = null;
-    private int lastRemovedAllPosition;
-    private int lastRemovedAppPosition;
 
     synchronized void clear() {
         states = new HashMap<>();
@@ -31,11 +29,24 @@ class MessageStateHolder {
         state.nextSince = pagedMessages.getPaging().getSince();
         state.appId = appId;
         states.put(appId, state);
+
+        // If there is a message with pending deletion, it should not reappear in the list in case
+        // it is added again.
+        if (deletionPending()) {
+            deleteMessage(pendingDeletion.getMessage());
+        }
     }
 
     synchronized void newMessage(Message message) {
+        // If there is a message with pending deletion, its indices are going to change. To keep
+        // them consistent the deletion is undone first and redone again after adding the new
+        // message.
+        MessageDeletion deletion = undoPendingDeletion();
+
         addMessage(message, 0, 0);
         lastReceivedMessage = message.getId();
+
+        if (deletion != null) deleteMessage(deletion.getMessage());
     }
 
     synchronized MessageState state(Integer appId) {
@@ -66,40 +77,48 @@ class MessageStateHolder {
         return lastReceivedMessage;
     }
 
-    synchronized void removeMessage(Message message) {
+    synchronized void deleteMessage(Message message) {
         MessageState allMessages = state(MessageState.ALL_MESSAGES);
         MessageState appMessages = state(message.getAppid());
 
+        int pendingDeletedAllPosition = -1;
+        int pendingDeletedAppPosition = -1;
+
         if (allMessages.loaded) {
             int allPosition = allMessages.messages.indexOf(message);
             allMessages.messages.remove(allPosition);
-            lastRemovedAllPosition = allPosition;
+            pendingDeletedAllPosition = allPosition;
         }
 
         if (appMessages.loaded) {
             int appPosition = appMessages.messages.indexOf(message);
             appMessages.messages.remove(appPosition);
-            lastRemovedAppPosition = appPosition;
+            pendingDeletedAppPosition = appPosition;
         }
 
-        lastRemovedMessage = message;
+        pendingDeletion =
+                new MessageDeletion(message, pendingDeletedAllPosition, pendingDeletedAppPosition);
     }
 
-    synchronized PositionPair undoLastRemoveMessage() {
+    synchronized MessageDeletion undoPendingDeletion() {
-        PositionPair result = null;
+        if (pendingDeletion != null)
-
+            addMessage(
-        if (lastRemovedMessage != null) {
+                    pendingDeletion.getMessage(),
-            addMessage(lastRemovedMessage, lastRemovedAllPosition, lastRemovedAppPosition);
+                    pendingDeletion.getAllPosition(),
-            result = new PositionPair(lastRemovedAllPosition, lastRemovedAppPosition);
+                    pendingDeletion.getAppPosition());
-
+        return purgePendingDeletion();
-            lastRemovedMessage = null;
-            lastRemovedAllPosition = -1;
-            lastRemovedAppPosition = -1;
     }
 
+    synchronized MessageDeletion purgePendingDeletion() {
+        MessageDeletion result = pendingDeletion;
+        pendingDeletion = null;
         return result;
     }
 
+    boolean deletionPending() {
+        return pendingDeletion != null;
+    }
+
     private void addMessage(Message message, int allPosition, int appPosition) {
         MessageState allMessages = state(MessageState.ALL_MESSAGES);
         MessageState appMessages = state(message.getAppid());