API Layer Design - tonglam/letletme_data GitHub Wiki

Overview

The API layer serves as the interface between external clients and our application's domain logic. It follows a functional programming approach using fp-ts, ensuring type safety and consistent error handling across all endpoints.

Architecture

graph TD
    Client[Client] --> API[API Layer]
    API --> Handlers[Handlers Layer]
    Handlers --> Services[Service Layer]
    Services --> Domain[Domain Layer]

    subgraph API Layer Components
        Routes[Routes] --> Middleware[Middleware]
        Routes --> TypeValidation[Type Validation]
        Routes --> ErrorHandling[Error Handling]
    end

Layer Structure

graph LR
    A[Routes] --> B[Handlers]
    B --> C[Services]

    subgraph API Layer
        A
        B
    end

    subgraph Service Layer
        C
    end

Core Design Principles

1. Functional Programming First

• Pure functions for predictable behavior
• Immutable data structures
• Effect handling through TaskEither
• Composition using fp-ts operators

2. Type Safety

• Runtime type validation with io-ts
• Compile-time type checking
• No implicit any types
• Strict null checks

3. Separation of Concerns

graph TD
    A[Routes] -->|HTTP Concerns| B[Request Handling]
    B -->|Business Logic| C[Domain Operations]
    C -->|Data Access| D[Service Layer]

4. Error Handling Strategy

graph LR
    A[Operation] -->|Success| B[Right]
    A -->|Failure| C[Left]
    B --> D[Success Response]
    C --> E[Error Response]

Domain API Organization

Structure

src/api/
├── handlers/       # Business logic handlers
├── middleware/     # Shared middleware
├── routes/         # Route definitions
├── types.ts        # API-specific type definitions
├── utils.ts        # API utility functions
└── index.ts        # API router configuration

Flow

sequenceDiagram
    participant C as Client
    participant R as Route
    participant H as Handler
    participant S as Service

    C->>R: HTTP Request
    R->>R: Validate Request
    R->>H: Call Handler
    H->>S: Service Operation
    S-->>H: Result
    H-->>R: Formatted Response
    R-->>C: HTTP Response

Response Format

Success

{
  status: 'success',
  data: T  // Generic type parameter
}

Error

{
  status: 'error',
  error: string
}

Security Design

Middleware Chain

graph LR
    A[Request] -->|1| B[Rate Limiting]
    B -->|2| C[Authentication]
    C -->|3| D[Validation]
    D -->|4| E[Handler]

Domain API Integration

Steps

1. Define domain types
2. Create handlers
3. Configure routes
4. Register with main router

Pattern

graph TD
    A[Domain Route] -->|1| B[Type Validation]
    B -->|2| C[Handler Logic]
    C -->|3| D[Service Call]
    D -->|4| E[Response Format]

Cross-Cutting Concerns

1. Logging

• Request/Response logging
• Error tracking
• Performance monitoring

2. Validation

• Request validation
• Response validation
• Runtime type checking

3. Error Management

• Consistent error format
• Error categorization
• Error recovery strategies

API Evolution Strategy

1. Versioning

• URL-based versioning
• Header-based versioning
• Content negotiation

2. Backwards Compatibility

• Deprecation strategy
• Migration support
• Documentation updates

Performance Considerations

1. Response Time

• Async operations
• Parallel processing
• Caching strategy

2. Scalability

• Stateless design
• Resource optimization
• Load balancing ready

Monitoring and Metrics

Key Metrics

• Response times
• Error rates
• Request volume
• Resource usage

Future Considerations

1. API Gateway Integration

• Rate limiting
• Authentication
• Request routing

2. Documentation

• OpenAPI/Swagger
• API documentation
• Integration guides