feat(demo): add new demo for showcasing backend messages lazy loading

src/test/java/com/flowingcode/vaadin/addons/chatassistant/ChatAssistantDemo.java

@@ -91,9 +91,6 @@ public void run() {
         .messageTime(LocalDateTime.now())
         .sender(Sender.builder().name("Assistant").avatar("chatbot.png").build()).build());
     chatAssistant.toggle();
-    chatAssistant.addSubmitListener(ev -> {
-      Notification.show(ev.getValue());
-    });
     Icon minimize = VaadinIcon.MINUS.create();
     minimize.addClickListener(ev -> chatAssistant.toggle());
     Span title = new Span("Customized Assistant Header");

src/test/java/com/flowingcode/vaadin/addons/chatassistant/ChatAssistantDemoView.java

@@ -33,6 +33,7 @@ public class ChatAssistantDemoView extends TabbedDemo {
 
   public ChatAssistantDemoView() {
     addDemo(ChatAssistantDemo.class);
+    addDemo(ChatAssistantLazyLoadingDemo.class);
     setSizeFull();
   }
 }

src/test/java/com/flowingcode/vaadin/addons/chatassistant/ChatAssistantLazyLoadingDemo.java

@@ -0,0 +1,107 @@
+/*-
+ * #%L
+ * Chat Assistant Add-on
+ * %%
+ * Copyright (C) 2023 Flowing Code
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * #L%
+ */
+package com.flowingcode.vaadin.addons.chatassistant;
+
+import com.flowingcode.vaadin.addons.chatassistant.model.Message;
+import com.flowingcode.vaadin.addons.chatassistant.model.Sender;
+import com.flowingcode.vaadin.addons.demo.DemoSource;
+import com.flowingcode.vaadin.addons.demo.SourcePosition;
+import com.google.common.base.Strings;
+import com.vaadin.flow.component.UI;
+import com.vaadin.flow.component.button.Button;
+import com.vaadin.flow.component.dependency.CssImport;
+import com.vaadin.flow.component.html.Span;
+import com.vaadin.flow.component.icon.Icon;
+import com.vaadin.flow.component.icon.VaadinIcon;
+import com.vaadin.flow.component.notification.Notification;
+import com.vaadin.flow.component.orderedlayout.HorizontalLayout;
+import com.vaadin.flow.component.orderedlayout.VerticalLayout;
+import com.vaadin.flow.component.textfield.TextArea;
+import com.vaadin.flow.data.provider.DataProvider;
+import com.vaadin.flow.router.PageTitle;
+import com.vaadin.flow.router.Route;
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Timer;
+
+@DemoSource(sourcePosition = SourcePosition.PRIMARY)
+@PageTitle("Lazy Loading Demo")
+@SuppressWarnings("serial")
+@Route(value = "chat-assistant/lazy-loading-demo", layout = ChatAssistantDemoView.class)
+@CssImport("./styles/chat-assistant-styles-demo.css")
+public class ChatAssistantLazyLoadingDemo extends VerticalLayout {
+
+  List<Message> messages = new ArrayList<Message>();
+
+  public ChatAssistantLazyLoadingDemo() {
+    ChatAssistant chatAssistant = new ChatAssistant();
+    Span lazyLoadingData = new Span();
+    DataProvider<Message,?> dataProvider = DataProvider.fromCallbacks(query->{
+      lazyLoadingData.setText("Loading messages from: " + query.getOffset() + ", with limit: " + query.getLimit());
+      return messages.stream().skip(query.getOffset()).limit(query.getLimit());
+    }, query->{
+      return messages.size();
+    });
+    chatAssistant.setDataProvider(dataProvider);
+
+    TextArea message = new TextArea();
+    message.setLabel("Enter a message from the assistant");
+    message.setSizeFull();
+    message.addKeyPressListener(ev->{
+      if (Strings.isNullOrEmpty(chatAssistant.getWhoIsTyping())) {
+        chatAssistant.setWhoIsTyping("Assistant is generating an answer ...");
+      }
+    });
+    message.addBlurListener(ev->chatAssistant.clearWhoIsTyping());
+
+    Button chat = new Button("Chat");
+    chat.addClickListener(ev -> {
+      Message m = Message.builder().content(message.getValue()).messageTime(LocalDateTime.now())
+          .sender(Sender.builder().name("Assistant").avatar("chatbot.png").build()).build();
+
+      messages.add(m);
+      dataProvider.refreshAll();
+      chatAssistant.scrollToEnd();
+      message.clear();
+    });
+    Message welcomeMessage = Message.builder().content("Hello, I am here to assist you")
+        .messageTime(LocalDateTime.now())
+        .sender(Sender.builder().name("Assistant").avatar("chatbot.png").build()).build();
+    messages.add(welcomeMessage);
+    chatAssistant.toggle();
+    chatAssistant.setSubmitListener(ev -> {
+      Message userMessage = Message.builder().messageTime(LocalDateTime.now())
+          .sender(Sender.builder().name("User").build()).content(ev.getValue()).build();
+      messages.add(userMessage);
+      dataProvider.refreshAll();
+      chatAssistant.scrollToEnd();
+    });
+    Icon minimize = VaadinIcon.MINUS.create();
+    minimize.addClickListener(ev -> chatAssistant.toggle());
+    Span title = new Span("Customized Assistant Header");
+    title.setWidthFull();
+    HorizontalLayout headerBar = new HorizontalLayout(title, minimize);
+    headerBar.setWidthFull();
+    chatAssistant.setHeaderComponent(headerBar);
+
+    add(message, lazyLoadingData, chat, chatAssistant);
+  }
+}