Refactor: Extract isDuplicateSystemMessage() to MessageAdapter

- Move duplicate message check logic to MessageAdapter for cleaner code
- Add reusable isDuplicateSystemMessage() helper method with documentation
- Simplify askUserToSelectModel() in MainActivity

Co-authored-by: kirklandsign <107070759+kirklandsign@users.noreply.github.com>

Author: Copilot

llm/android/LlamaDemo/app/src/main/java/com/example/executorchllamademo/MainActivity.java

@@ -461,14 +461,7 @@ private void askUserToSelectModel() {
     ETLogging.getInstance().log(askLoadModel);
     runOnUiThread(
         () -> {
-          // Only add the message if it's not already the last message in the chat
-          int messageCount = mMessageAdapter.getCount();
-          Message lastMessage = messageCount > 0 ? mMessageAdapter.getItem(messageCount - 1) : null;
-          boolean isDuplicate =
-              lastMessage != null
-                  && lastMessage.getMessageType() == MessageType.SYSTEM
-                  && askLoadModel.equals(lastMessage.getText());
-          if (!isDuplicate) {
+          if (!mMessageAdapter.isDuplicateSystemMessage(askLoadModel)) {
             mMessageAdapter.add(askLoadModelMessage);
             mMessageAdapter.notifyDataSetChanged();
           }

llm/android/LlamaDemo/app/src/main/java/com/example/executorchllamademo/MessageAdapter.java

@@ -132,4 +132,21 @@ public int getMaxPromptID() {
     }
     return maxPromptID;
   }
+
+  /**
+   * Checks if the last message is a duplicate system message with the given text.
+   *
+   * @param text The text to check against the last message
+   * @return true if the last message is a system message with matching text, false otherwise
+   */
+  public boolean isDuplicateSystemMessage(String text) {
+    int count = getCount();
+    if (count == 0) {
+      return false;
+    }
+    Message lastMessage = getItem(count - 1);
+    return lastMessage != null
+        && lastMessage.getMessageType() == MessageType.SYSTEM
+        && text.equals(lastMessage.getText());
+  }
 }