pkgs/dart_mcp/lib/src/server/prompts_support.dart

// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of 'server.dart';

/// A mixin for MCP servers which support the `prompts` capability.
///
/// Call [addPrompt] to add new prompts, and [removePrompt] to delete prompts,
/// these are typically done in the [initialize] method, but may be done at any
/// time.
///
/// Supports `listChanged` notifications for changes to the prompts list.
///
/// See https://modelcontextprotocol.io/docs/concepts/prompts.
base mixin PromptsSupport on MCPServer {
  /// The added prompts by name.
  final Map<String, Prompt> _prompts = {};

  /// The added prompt implementations by name.
  final Map<String, FutureOr<GetPromptResult> Function(GetPromptRequest)>
  _promptImpls = {};

  @override
  FutureOr<InitializeResult> initialize(InitializeRequest request) async {
    registerRequestHandler(ListPromptsRequest.methodName, _listPrompts);

    registerRequestHandler(GetPromptRequest.methodName, _getPrompt);

    final result = await super.initialize(request);
    (result.capabilities.prompts ??= Prompts()).listChanged = true;
    return result;
  }

  /// Lists the available prompts.
  ListPromptsResult _listPrompts(ListPromptsRequest request) =>
      ListPromptsResult(prompts: _prompts.values.toList());

  /// Gets the response for a given prompt.
  FutureOr<GetPromptResult> _getPrompt(GetPromptRequest request) {
    final impl = _promptImpls[request.name];
    if (impl == null) {
      throw ArgumentError.value(request.name, 'name', 'Prompt not found');
    }
    return impl(request);
  }

  /// Adds a prompt and notifies clients that the list has changed.
  void addPrompt(
    Prompt prompt,
    FutureOr<GetPromptResult> Function(GetPromptRequest) impl,
  ) {
    if (_prompts.containsKey(prompt.name)) {
      throw StateError(
        'Failed to add prompt ${prompt.name}, it already exists',
      );
    }
    _prompts[prompt.name] = prompt;
    _promptImpls[prompt.name] = impl;
    if (ready) {
      _notifyPromptListChanged();
    }
  }

  /// Removes a prompt and notifies clients that the list has changed.
  void removePrompt(String name) {
    _prompts.remove(name);
    _promptImpls.remove(name);
    if (ready) {
      _notifyPromptListChanged();
    }
  }

  /// Notifies clients that the prompts list has changed.
  void _notifyPromptListChanged() => sendNotification(
    PromptListChangedNotification.methodName,
    PromptListChangedNotification(),
  );
}