feat(firebaseai): add thinking feature

packages/firebase_ai/firebase_ai/example/lib/main.dart

@@ -167,7 +167,10 @@ class _HomeScreenState extends State<HomeScreen> {
   ) {
     switch (index) {
       case 0:
-        return ChatPage(title: 'Chat', model: currentModel);
+        return ChatPage(
+          title: 'Chat',
+          useVertexBackend: useVertexBackend,
+        );
       case 1:
         return AudioPage(title: 'Audio', model: currentModel);
       case 2:
@@ -199,7 +202,10 @@ class _HomeScreenState extends State<HomeScreen> {
 
       default:
         // Fallback to the first page in case of an unexpected index
-        return ChatPage(title: 'Chat', model: currentModel);
+        return ChatPage(
+          title: 'Chat',
+          useVertexBackend: useVertexBackend,
+        );
     }
   }
 

packages/firebase_ai/firebase_ai/example/lib/pages/audio_page.dart

@@ -99,7 +99,7 @@ class _AudioPageState extends State<AudioPage> {
   Future<void> _submitAudioToModel(audioPart) async {
     try {
       String textPrompt = 'What is in the audio recording?';
-      final prompt = TextPart('What is in the audio recording?');
+      const prompt = TextPart('What is in the audio recording?');
 
       setState(() {
         _messages.add(MessageData(text: textPrompt, fromUser: true));
@@ -137,11 +137,6 @@ class _AudioPageState extends State<AudioPage> {
                 itemBuilder: (context, idx) {
                   return MessageWidget(
                     text: _messages[idx].text,
-                    image: Image.memory(
-                      _messages[idx].imageBytes!,
-                      cacheWidth: 400,
-                      cacheHeight: 400,
-                    ),
                     isFromUser: _messages[idx].fromUser ?? false,
                   );
                 },

packages/firebase_ai/firebase_ai/example/lib/pages/chat_page.dart

@@ -12,32 +12,58 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import 'package:firebase_auth/firebase_auth.dart';
 import 'package:flutter/material.dart';
 import 'package:firebase_ai/firebase_ai.dart';
 import '../widgets/message_widget.dart';
 
 class ChatPage extends StatefulWidget {
-  const ChatPage({super.key, required this.title, required this.model});
+  const ChatPage({
+    super.key,
+    required this.title,
+    required this.useVertexBackend,
+  });
 
   final String title;
-  final GenerativeModel model;
+  final bool useVertexBackend;
 
   @override
   State<ChatPage> createState() => _ChatPageState();
 }
 
 class _ChatPageState extends State<ChatPage> {
   ChatSession? _chat;
+  GenerativeModel? _model;
   final ScrollController _scrollController = ScrollController();
   final TextEditingController _textController = TextEditingController();
   final FocusNode _textFieldFocus = FocusNode();
   final List<MessageData> _messages = <MessageData>[];
   bool _loading = false;
+  bool _enableThinking = false;
 
   @override
   void initState() {
     super.initState();
-    _chat = widget.model.startChat();
+    _initializeChat();
+  }
+
+  void _initializeChat() {
+    final generationConfig = GenerationConfig(
+      thinkingConfig:
+          _enableThinking ? ThinkingConfig(includeThoughts: true) : null,
+    );
+    if (widget.useVertexBackend) {
+      _model = FirebaseAI.vertexAI(auth: FirebaseAuth.instance).generativeModel(
+        model: 'gemini-2.5-flash',
+        generationConfig: generationConfig,
+      );
+    } else {
+      _model = FirebaseAI.googleAI(auth: FirebaseAuth.instance).generativeModel(
+        model: 'gemini-2.5-flash',
+        generationConfig: generationConfig,
+      );
+    }
+    _chat = _model?.startChat();
   }
 
   void _scrollDown() {
@@ -64,18 +90,31 @@ class _ChatPageState extends State<ChatPage> {
           mainAxisAlignment: MainAxisAlignment.center,
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
+            SwitchListTile(
+              title: const Text('Enable Thinking'),
+              value: _enableThinking,
+              onChanged: (bool value) {
+                setState(() {
+                  _enableThinking = value;
+                  _initializeChat();
+                });
+              },
+            ),
             Expanded(
               child: ListView.builder(
                 controller: _scrollController,
                 itemBuilder: (context, idx) {
+                  final message = _messages[idx];
                   return MessageWidget(
-                    text: _messages[idx].text,
-                    image: Image.memory(
-                      _messages[idx].imageBytes!,
-                      cacheWidth: 400,
-                      cacheHeight: 400,
-                    ),
-                    isFromUser: _messages[idx].fromUser ?? false,
+                    text: message.text,
+                    image: message.imageBytes != null
+                        ? Image.memory(
+                            message.imageBytes!,
+                            cacheWidth: 400,
+                            cacheHeight: 400,
+                          )
+                        : null,
+                    isFromUser: message.fromUser ?? false,
                   );
                 },
                 itemCount: _messages.length,
@@ -130,6 +169,11 @@ class _ChatPageState extends State<ChatPage> {
       var response = await _chat?.sendMessage(
         Content.text(message),
       );
+      final thought = response?.thoughtSummary;
+      if (thought != null) {
+        _messages
+            .add(MessageData(text: thought, fromUser: false, isThought: true));
+      }
       var text = response?.text;
       _messages.add(MessageData(text: text, fromUser: false));
 

packages/firebase_ai/firebase_ai/example/lib/pages/document.dart

@@ -47,7 +47,7 @@ class _DocumentPageState extends State<DocumentPage> {
       const _prompt =
           'Write me a summary in one sentence what this document is about.';
 
-      final prompt = TextPart(_prompt);
+      const prompt = TextPart(_prompt);
 
       setState(() {
         _messages.add(MessageData(text: _prompt, fromUser: true));

packages/firebase_ai/firebase_ai/example/lib/pages/function_calling_page.dart

@@ -39,28 +39,39 @@ class Location {
 }
 
 class _FunctionCallingPageState extends State<FunctionCallingPage> {
-  late final GenerativeModel _functionCallModel;
+  late GenerativeModel _functionCallModel;
   final List<MessageData> _messages = <MessageData>[];
   bool _loading = false;
+  bool _enableThinking = false;
 
   @override
   void initState() {
     super.initState();
+    _initializeModel();
+  }
+
+  void _initializeModel() {
+    final generationConfig = GenerationConfig(
+      thinkingConfig:
+          _enableThinking ? ThinkingConfig(includeThoughts: true) : null,
+    );
     if (widget.useVertexBackend) {
       var vertexAI = FirebaseAI.vertexAI(auth: FirebaseAuth.instance);
       _functionCallModel = vertexAI.generativeModel(
-        model: 'gemini-2.0-flash',
+        model: 'gemini-2.5-flash',
         tools: [
           Tool.functionDeclarations([fetchWeatherTool]),
         ],
+        generationConfig: generationConfig,
       );
     } else {
       var googleAI = FirebaseAI.googleAI(auth: FirebaseAuth.instance);
       _functionCallModel = googleAI.generativeModel(
-        model: 'gemini-2.0-flash',
+        model: 'gemini-2.5-flash',
         tools: [
           Tool.functionDeclarations([fetchWeatherTool]),
         ],
+        generationConfig: generationConfig,
       );
     }
   }
@@ -118,12 +129,24 @@ class _FunctionCallingPageState extends State<FunctionCallingPage> {
           mainAxisAlignment: MainAxisAlignment.center,
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
+            SwitchListTile(
+              title: const Text('Enable Thinking'),
+              value: _enableThinking,
+              onChanged: (bool value) {
+                setState(() {
+                  _enableThinking = value;
+                  _initializeModel();
+                });
+              },
+            ),
             Expanded(
               child: ListView.builder(
                 itemBuilder: (context, idx) {
+                  final message = _messages[idx];
                   return MessageWidget(
-                    text: _messages[idx].text,
-                    isFromUser: _messages[idx].fromUser ?? false,
+                    text: message.text,
+                    isFromUser: message.fromUser ?? false,
+                    isThought: message.isThought,
                   );
                 },
                 itemCount: _messages.length,
@@ -158,43 +181,87 @@ class _FunctionCallingPageState extends State<FunctionCallingPage> {
   Future<void> _testFunctionCalling() async {
     setState(() {
       _loading = true;
+      _messages.clear();
     });
-    final functionCallChat = _functionCallModel.startChat();
-    const prompt = 'What is the weather like in Boston on 10/02 in year 2024?';
+    try {
+      final functionCallChat = _functionCallModel.startChat();
+      const prompt =
+          'What is the weather like in Boston on 10/02 in year 2024?';
 
-    // Send the message to the generative model.
-    var response = await functionCallChat.sendMessage(
-      Content.text(prompt),
-    );
+      _messages.add(MessageData(text: prompt, fromUser: true));
 
-    final functionCalls = response.functionCalls.toList();
-    // When the model response with a function call, invoke the function.
-    if (functionCalls.isNotEmpty) {
-      final functionCall = functionCalls.first;
-      if (functionCall.name == 'fetchWeather') {
-        Map<String, dynamic> location =
-            functionCall.args['location']! as Map<String, dynamic>;
-        var date = functionCall.args['date']! as String;
-        var city = location['city'] as String;
-        var state = location['state'] as String;
-        final functionResult = await fetchWeather(Location(city, state), date);
-        // Send the response to the model so that it can use the result to
-        // generate text for the user.
-        response = await functionCallChat.sendMessage(
-          Content.functionResponse(functionCall.name, functionResult),
-        );
-      } else {
-        throw UnimplementedError(
-          'Function not declared to the model: ${functionCall.name}',
-        );
+      // Send the message to the generative model.
+      var response = await functionCallChat.sendMessage(
+        Content.text(prompt),
+      );
+
+      final thought = response.thoughtSummary;
+      if (thought != null) {
+        _messages
+            .add(MessageData(text: thought, fromUser: false, isThought: true));
       }
-    }
-    // When the model responds with non-null text content, print it.
-    if (response.text case final text?) {
-      _messages.add(MessageData(text: text));
+
+      final functionCalls = response.functionCalls.toList();
+      // When the model response with a function call, invoke the function.
+      if (functionCalls.isNotEmpty) {
+        final functionCall = functionCalls.first;
+        if (functionCall.name == 'fetchWeather') {
+          Map<String, dynamic> location =
+              functionCall.args['location']! as Map<String, dynamic>;
+          var date = functionCall.args['date']! as String;
+          var city = location['city'] as String;
+          var state = location['state'] as String;
+          final functionResult =
+              await fetchWeather(Location(city, state), date);
+          // Send the response to the model so that it can use the result to
+          // generate text for the user.
+          response = await functionCallChat.sendMessage(
+            Content.functionResponse(functionCall.name, functionResult),
+          );
+        } else {
+          throw UnimplementedError(
+            'Function not declared to the model: ${functionCall.name}',
+          );
+        }
+      }
+      // When the model responds with non-null text content, print it.
+      if (response.text case final text?) {
+        _messages.add(MessageData(text: text));
+        setState(() {
+          _loading = false;
+        });
+      }
+    } catch (e) {
+      _showError(e.toString());
+      setState(() {
+        _loading = false;
+      });
+    } finally {
       setState(() {
         _loading = false;
       });
     }
   }
+
+  void _showError(String message) {
+    showDialog<void>(
+      context: context,
+      builder: (context) {
+        return AlertDialog(
+          title: const Text('Something went wrong'),
+          content: SingleChildScrollView(
+            child: SelectableText(message),
+          ),
+          actions: [
+            TextButton(
+              onPressed: () {
+                Navigator.of(context).pop();
+              },
+              child: const Text('OK'),
+            ),
+          ],
+        );
+      },
+    );
+  }
 }

packages/firebase_ai/firebase_ai/example/lib/pages/image_prompt_page.dart

@@ -188,7 +188,7 @@ class _ImagePromptPageState extends State<ImagePromptPage> {
       final content = [
         Content.multi([
           TextPart(message),
-          FileData(
+          const FileData(
             'image/jpeg',
             'gs://vertex-ai-example-ef5a2.appspot.com/foodpic.jpg',
           ),

packages/firebase_ai/firebase_ai/example/lib/pages/video_page.dart

@@ -46,8 +46,6 @@ class _VideoPageState extends State<VideoPage> {
 
       const _prompt = 'Can you tell me what is in the video?';
 
-      final prompt = TextPart(_prompt);
-
       setState(() {
         _messages.add(MessageData(text: _prompt, fromUser: true));
       });
@@ -56,7 +54,7 @@ class _VideoPageState extends State<VideoPage> {
           InlineDataPart('video/mp4', videoBytes.buffer.asUint8List());
 
       final response = await widget.model.generateContent([
-        Content.multi([prompt, videoPart]),
+        Content.multi([const TextPart(_prompt), videoPart]),
       ]);
 
       setState(() {