# MCP Module - Quick Reference & Testing Guide

## 📋 Module at a Glance

| Aspect | Details |
|--------|---------|
| **Location** | `apps/api/src/modules/mcp/` |
| **Total Files** | 4 source files |
| **Test Files** | 1 test file (174 lines) |
| **Architecture** | Presentation layer only |
| **Testing Framework** | Vitest |
| **Test Coverage** | Controller well tested ✅ |

## 📁 Complete File Listing

```
MCP Module Files:
✅ index.ts (1 line)
✅ mcp.module.ts (22 lines)
✅ presentation/mcp-transport.controller.ts (102 lines)
✅ presentation/__tests__/mcp-transport.controller.spec.ts (174 lines)
```

## 🏗️ Architecture

### Current (Simplified - Presentation Only)
```
Presentation Layer ✅
├── McpTransportController
│   ├── GET /mcp/servers
│   ├── GET /mcp/:serverName/sse  
│   └── POST /mcp/:serverName/messages
└── Tests (174 lines)

McpIntegrationModule (22 lines)
├── Module config
├── Service setup
└── Module lifecycle
```

### Missing Layers (Not Implemented)
```
❌ Domain Layer (no entities, events, business logic)
❌ Application Layer (no handlers, commands, queries)
❌ Infrastructure Layer (no repositories, adapters)
```

## 🧪 Testing Overview

### Test File: mcp-transport.controller.spec.ts (174 lines)
- **Total Tests**: 11
- **Test Suites**: 4 describe blocks
- **Coverage**: 100% of controller endpoints

### Test Breakdown
```
1. Security Decorators (4 tests)
   ├── JwtAuthGuard applied
   ├── listServers throttle (30 req/60s)
   ├── handleSse throttle (5 req/60s) ⚡ stricter
   └── handleMessage throttle (30 req/60s)

2. listServers (2 tests)
   ├── Returns server list
   └── Handles empty list

3. handleSse (3 tests)
   ├── Throws NOT_FOUND for missing server
   ├── Creates transport & connects
   └── Cleans up on connection close

4. handleMessage (2 tests)
   ├── Throws BAD_REQUEST for missing sessionId
   └── Throws NOT_FOUND for expired session
```

## 🎯 Key Classes

### McpIntegrationModule
```typescript
class McpIntegrationModule implements OnModuleInit {
  constructor(
    typesenseClient: TypesenseClientService,
    mcpRegistry: McpRegistryService,
    logger: LoggerService,
  ) {}
  
  async onModuleInit(): Promise<void> {
    // Set typesense client, re-initialize servers, log results
  }
}
```

### McpTransportController
```typescript
@Controller('mcp')
@UseGuards(JwtAuthGuard)
class McpTransportController {
  listServers(): { servers: string[] }
  
  async handleSse(serverName, user, req, res): Promise<void>
  
  async handleMessage(serverName, user, req, res): Promise<void>
}
```

## 🔧 Testing Patterns

### Module Mocking
```typescript
vi.mock('@goodgo/mcp-servers', () => ({
  SSEServerTransport: class MockSSE {
    sessionId = 'mock-session-id';
    handlePostMessage = vi.fn().mockResolvedValue(undefined);
  },
}));
```

### Service Mocking
```typescript
mockRegistry = {
  getServerNames: vi.fn(),
  getServer: vi.fn(),
};
```

### Decorator Verification
```typescript
const guards = Reflect.getMetadata('__guards__', McpTransportController);
const throttleLimit = Reflect.getMetadata('THROTTLER:LIMITdefault', method);
```

## 📚 Testing Examples from Other Modules

### Auth Module Pattern (Simple)
- Minimal dependencies
- Direct handler instantiation
- Focus on behavior verification

### Payments Module Pattern (Complex)
- Multiple dependency mocks
- Business rule testing  
- Event bus verification

### Domain Entity Pattern
- Explicit vitest imports
- State transition testing
- Domain event verification
- Error handling with Result types

### Infrastructure Pattern
- External service simulation
- Security testing (crypto)
- Complex test data builders

## 🚀 Running Tests

```bash
# Run all MCP tests
pnpm test -- src/modules/mcp

# Run with watch
pnpm test -- --watch src/modules/mcp

# Run with coverage
pnpm test -- --coverage src/modules/mcp

# Run specific test
pnpm test -- src/modules/mcp/presentation/__tests__/mcp-transport.controller.spec.ts
```

## 💡 Recommendations

### High Priority
- ✅ Controller is well tested - maintain this
- 📝 Add tests for McpIntegrationModule.onModuleInit()
- 📝 Test module dependency injection

### Lower Priority
- 🏗️ If domain logic added, follow payments patterns
- 🏗️ If handlers added, use CQRS patterns
- 🏗️ Add integration tests for SSE lifecycle