工具调用（又称函数调用）

// Look up the metadata for a word in the dictionary API.
Future<Map<String, dynamic>> _getWordMetadataFromApi(String word) async {
  final url = Uri.parse(
    'https://api.dictionaryapi.dev/api/v2/entries/en/${Uri.encodeComponent(word)}',
  );
​
  final response = await http.get(url);
  return response.statusCode == 200
      ? {'result': jsonDecode(response.body)}
      : {'error': 'Could not find a definition for "$word".'};
}

// The model for solving clues.
_clueSolverModel = FirebaseAI.googleAI().generativeModel(
  model: 'gemini-2.5-flash',
  systemInstruction: Content.text(clueSolverSystemInstruction),
  tools: [
    Tool.functionDeclarations([
      FunctionDeclaration(
        'getWordMetadata',
        'Gets grammatical metadata for a word, like its part of speech. '
        'Best used to verify a candidate answer against a clue that implies a '
        'grammatical constraint.',
        parameters: {
           'word': Schema(SchemaType.string, description: 'The word to look up.'),
         },
       ),
    ]),
  ],
);

static String get clueSolverSystemInstruction =>
    '''
You are an expert crossword puzzle solver.
​
...
​
### Tool: `getWordMetadata`
​
You have a tool to get grammatical information about a word.
​
**When to use:**
- This tool is most helpful as a verification step after you have a likely answer.
- Consider using this tool when a clue contains a grammatical hint that could be ambiguous.
- **Good candidates for verification:**
  - Clues that seem to be verbs (e.g., "To run," "Waving").
  - Clues that are adverbs (e.g., "Happily," "Quickly").
  - Clues that specify a plural form.
- **Try to avoid using the tool for:**
  - Simple definitions (e.g., "A small dog").
  - Fill-in-the-blank clues (e.g., "___ and flow").
  - Proper nouns (e.g., "Capital of France").
​
**Function signature:**
```json
${jsonEncode(_getWordMetadataFunction.toJson())}
```
''';

extension on GenerativeModel {
  Future<String> generateContentWithFunctions({
    required String prompt,
    required Future<Map<String, dynamic>> Function(FunctionCall) onFunctionCall,
  }) async {
    // Use a chat session to support multiple request/response pairs, which is
    // needed to support function calls.
    final chat = startChat();
    final buffer = StringBuffer();
    var response = await chat.sendMessage(Content.text(prompt));
​
    while (true) {
      // Append the response text to the buffer.
      buffer.write(response.text ?? '');
​
      // If no function calls were collected, we're done
      if (response.functionCalls.isEmpty) break;
​
      // Append a newline to separate responses.
      buffer.write('\n');
​
      // Execute all function calls
      final functionResponses = <FunctionResponse>[];
      for (final functionCall in response.functionCalls) {
        try {
          functionResponses.add(
            FunctionResponse(
              functionCall.name,
              await onFunctionCall(functionCall),
            ),
          );
        } catch (ex) {
          functionResponses.add(
            FunctionResponse(functionCall.name, {'error': ex.toString()}),
          );
        }
      }
​
      // Get the next response stream with function results
      response = await chat.sendMessage(
        Content.functionResponses(functionResponses),
      );
    }
​
    return buffer.toString();
  }
}

await _clueSolverModel.generateContentWithFunctions(
  prompt: getSolverPrompt(clue, length, pattern),
  onFunctionCall: (functionCall) async => switch (functionCall.name) {
    'getWordMetadata' => await _getWordMetadataFromApi(
      functionCall.args['word'] as String,
    ),
    _ => throw Exception('Unknown function call: ${functionCall.name}'),
  },
);

 // The model for solving clues.
_clueSolverModel = FirebaseAI.googleAI().generativeModel(
  model: 'gemini-2.5-flash',
  systemInstruction: Content.text(clueSolverSystemInstruction),
  tools: [
    Tool.functionDeclarations([
      ...,
      FunctionDeclaration(
        'returnResult',
        'Returns the final result of the clue solving process.',
        parameters: {
        'answer': Schema(
          SchemaType.string,
          description: 'The answer to the clue.',
        ),
        'confidence': Schema(
          SchemaType.number,
          description: 'The confidence score in the answer from 0.0 to 1.0.',
          ),
        },
      ),
    ]),
  ],
);

static String get clueSolverSystemInstruction =>
    '''
You are an expert crossword puzzle solver.
​
...
​
### Tool: `returnResult`
​
You have a tool to return the final result of the clue solving process.
​
**When to use:**
- Use this tool when you have a final answer and confidence score to return. You
must use this tool exactly once, and only once, to return the final result.
​
**Function signature:**
```json
${jsonEncode(_returnResultFunction.toJson())}
```
''';

// Buffer for the result of the clue solving process.
final _returnResult = <String, dynamic>{};
​
// Cache the return result of the clue solving process via a function call.
// This is how we get JSON responses from the model with functions, since the
// model cannot return JSON directly when tools are used.
Map<String, dynamic> _cacheReturnResult(Map<String, dynamic> returnResult) {
  assert(_returnResult.isEmpty);
  _returnResult.addAll(returnResult);
  return {'status': 'success'};
}
​
Future<ClueAnswer?> solveClue(Clue clue, int length, String pattern) async {
  // Clear the return result cache; this is where the result will be stored.
  _returnResult.clear();
​
  // Generate JSON response with functions and schema.
  await _clueSolverModel.generateContentWithFunctions(
    prompt: getSolverPrompt(clue, length, pattern),
    onFunctionCall: (functionCall) async => switch (functionCall.name) {
      'getWordMetadata' => ...,
      'returnResult' => _cacheReturnResult(functionCall.args),
      _ => throw Exception('Unknown function call: ${functionCall.name}'),
    },
  );
​
  // Use the structured output that the LLM has called function with
  assert(_returnResult.isNotEmpty);
  return ClueAnswer(
    answer: _returnResult['answer'] as String,
    confidence: (_returnResult['confidence'] as num).toDouble(),
  );
}

​
// The new function to let the LLM resolve solution conflicts
static final _resolveConflictFunction = FunctionDeclaration(
  'resolveConflict',
  'Asks the user to resolve a conflict between the letter pattern and the '
  'proposed answer. Use this BEFORE calling returnResult if the answer you '
  'want to propose does not match the letter pattern.',
  parameters: {
    'proposedAnswer': Schema(
      SchemaType.string,
      description: 'The answer the LLM wants to suggest.',
    ),
    'pattern': Schema(
      SchemaType.string,
      description: 'The current letter pattern from the grid.',
    ),
    'clue': Schema(SchemaType.string, description: 'The clue text.'),
  },
);
​
// Pass the new tool to the model for solving clues.
final _clueSolverModel = FirebaseAI.googleAI().generativeModel(
  model: 'gemini-2.5-flash',
  systemInstruction: Content.text(clueSolverSystemInstruction),
  tools: [
    Tool.functionDeclarations([
      ...
      _resolveConflictFunction,
    ]),
  ],
);
// Let the LLM know that it has a new tool.
static String get clueSolverSystemInstruction =>
    '''
You are an expert crossword puzzle solver.
​
...
​
### Tool: `resolveConflict`
​
You have a tool to ask the user to resolve a conflict.
​
**When to use:**
- Use this tool **BEFORE** `returnResult` if your proposed answer conflicts with the provided letter pattern.
- For example, if the pattern is `_ R _ Y` and you want to suggest `RENT` (which fits the clue), there is a conflict at the second letter (`R` vs `E`). You should call `resolveConflict(proposedAnswer: "RENT", pattern: "_ R _ Y", clue: "...")`.
- The tool will return the user's decision (either your proposed answer or a new one). You should then use that result to call `returnResult`.
​
**Function signature:**
```json
${jsonEncode(_resolveConflictFunction.toJson())}
```
''';

// handle the LLM's request to resolve the conflict
await _clueSolverModel.generateContentWithFunctions(
  prompt: getSolverPrompt(clue, length, pattern),
  onFunctionCall: (functionCall) async => switch (functionCall.name) {
    ...
    'resolveConflict' => await _handleResolveConflict(
      functionCall.args,
      onConflict,
    ),
  },
);
​
// Show the dialog to gather the user's input
Future<Map<String, dynamic>> _handleResolveConflict(
  Map<String, dynamic> args,
  Future<String> Function(String clue, String proposedAnswer, String pattern)?
  onConflict,
) async {
  final proposedAnswer = args['proposedAnswer'] as String;
  final pattern = args['pattern'] as String;
  final clue = args['clue'] as String;
​
  if (onConflict != null) {
    final result = await onConflict(clue, proposedAnswer, pattern);
    return {'result': result};
  }
​
  return {'result': proposedAnswer};
}