Refactor generic_chat to separate code destined for SDK from main etc.

[jacobsimionato]

Add WidgetTreeLlmAdapter which contains all the code to manage a conversation. This leaves main.dart to simply configure the widget library and define the system prompt.

[gemini-code-assist]

Code Review

This pull request successfully refactors the generic_chat example by introducing a WidgetTreeLlmAdapter to encapsulate conversation management and LLM interaction logic. This significantly cleans up main.dart, leaving it with just configuration and setup responsibilities. The introduction of an LlmConnection interface is a great step towards better abstraction and testability.

My review includes suggestions to improve code clarity, maintainability, and error handling:

• Standardizing indentation in the system prompt.
• Reducing code duplication in ConversationWidget.
• Improving error handling by using debugPrint over print and providing user feedback for errors.
• Removing dead code from a StreamBuilder.

[gemini-code-assist]

The indentation within the systemPrompt multiline string is inconsistent. The first paragraph is not indented, while the subsequent paragraphs have significant leading whitespace. This could affect how the LLM interprets the prompt and also makes the code harder to read.

For consistency and predictability, it's best to have uniform indentation for all paragraphs.

final systemPrompt =
    '''You are a helpful assistant who figures out what the user wants to do and then helps suggest options so they can develop a plan and find relevant information.

The user will ask questions, and you will respond by generating appropriate UI elements. Typically, you will first elicit more information to understand the user's needs, then you will start displaying information and the user's plans.

For example, the user may say \"I want to plan a trip to Mexico\". You will first ask some questions by displaying a combination of UI elements, such as a slider to choose budget, options showing activity preferences etc. Then you will walk the user through choosing a hotel, flight and accomodation.

Typically, you should not update existing surfaces and instead just continually \"add\" new ones.
''';

[gemini-code-assist]

There's repeated code for styling the Card widgets within the switch statement. Each case (SystemMessage, TextResponse, UserPrompt, UiResponse) defines a Card with the same elevation and margin.

To improve maintainability and reduce duplication, you could extract this into a shared private widget.

For example:

class _MessageCard extends StatelessWidget {
  const _MessageCard({required this.child});
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 2.0,
      margin: const EdgeInsets.symmetric(horizontal: 8.0, vertical: 4.0),
      child: child,
    );
  }
}

// Then in your switch:
return switch (message) {
  SystemMessage() => _MessageCard(
      child: ListTile(
        title: Text(message.text),
        leading: const Icon(Icons.smart_toy_outlined),
      ),
    ),
  // ... and so on for other cases
}

[gemini-code-assist]

The TODO comment correctly identifies that this error handling can be improved. Using print() is not ideal for logging in Flutter apps; debugPrint() is preferred as it avoids being throttled on Android.

Additionally, this error should be surfaced to the user, for instance by adding a SystemMessage to the chat history, similar to how other errors are handled in _generateAndSendResponse.

        // TODO: Handle error - unknown surfaceId
        debugPrint('Unknown surfaceId: $surfaceId');
        _chatHistory.add(SystemMessage(text: 'Error: Unknown surfaceId: $surfaceId'));
        _uiDataStreamController.add(List.from(_chatHistory));
        continue;

[gemini-code-assist]

The TODO here indicates that error handling can be improved. While adding a SystemMessage to the chat is great for user feedback, using print() for logging is not ideal. debugPrint() is a better choice in Flutter as it's not throttled on Android. For more robust logging, consider integrating a logging package.

      debugPrint('Error generating content: $e');

[gemini-code-assist]

The else block in this StreamBuilder is unreachable. Because you provide non-null initialData, snapshot.hasData will be true from the very first build, so the else branch containing the CircularProgressIndicator will never be executed. You can simplify this by removing the conditional logic.

          // Since `initialData` is provided, `snapshot.data` will not be null,
          // and `snapshot.hasData` will always be true.
          return ConversationWidget(
              messages: snapshot.data!,
              catalog: catalog,
              onEvent: (event) {
                _eventDebouncer.add(UiEvent.fromMap(event));
              });