Implement best practices and comprehensive documentation

ARCHITECTURE.md

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+# PolarisShu Architecture
+
+## Overview
+
+PolarisShu is a full-stack monorepo application built with modern web technologies. It follows a client-server architecture with a clear separation between frontend and backend concerns.
+
+## Tech Stack
+
+### Backend
+- **Language**: Rust (2024 Edition)
+- **Web Framework**: Salvo 0.82
+- **Async Runtime**: Tokio
+- **Serialization**: Serde
+- **Logging**: Tracing + Tracing-Subscriber
+- **API Documentation**: OpenAPI 3.1 + Swagger UI
+
+### Frontend
+- **Language**: TypeScript 5.8
+- **Framework**: React 19
+- **Build Tool**: Vite 7
+- **Styling**: Tailwind CSS 4
+- **HTTP Client**: Axios
+- **Type Generation**: openapi-typescript
+
+## Architecture Diagram
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                         Frontend                             │
+│  ┌─────────────────────────────────────────────────────┐   │
+│  │  React Components                                    │   │
+│  │  ├── App.tsx (Main Application)                      │   │
+│  │  ├── UserList.tsx (User Display)                     │   │
+│  │  └── ErrorBoundary.tsx (Error Handling)             │   │
+│  └─────────────────┬───────────────────────────────────┘   │
+│                    │                                         │
+│  ┌─────────────────▼───────────────────────────────────┐   │
+│  │  Services Layer                                      │   │
+│  │  └── api.ts (API Client with Axios)                 │   │
+│  └─────────────────┬───────────────────────────────────┘   │
+└────────────────────┼─────────────────────────────────────────┘
+                     │ HTTP Requests
+                     │ (Vite Proxy: /api → localhost:8080)
+┌────────────────────▼─────────────────────────────────────────┐
+│                         Backend                              │
+│  ┌─────────────────────────────────────────────────────┐   │
+│  │  Router & Middleware                                 │   │
+│  │  ├── CORS Handler                                    │   │
+│  │  └── Routes Configuration                            │   │
+│  └─────────────────┬───────────────────────────────────┘   │
+│                    │                                         │
+│  ┌─────────────────▼───────────────────────────────────┐   │
+│  │  API Handlers (Endpoints)                            │   │
+│  │  ├── GET /api/health (Health Check)                 │   │
+│  │  ├── GET /api/users (List Users)                    │   │
+│  │  ├── GET /swagger-ui (API Documentation)            │   │
+│  │  └── GET /api-docs/openapi.json (OpenAPI Spec)      │   │
+│  └─────────────────┬───────────────────────────────────┘   │
+│                    │                                         │
+│  ┌─────────────────▼───────────────────────────────────┐   │
+│  │  Models & Business Logic                             │   │
+│  │  ├── User Model                                      │   │
+│  │  └── HealthResponse Model                            │   │
+│  └─────────────────────────────────────────────────────┘   │
+└──────────────────────────────────────────────────────────────┘
+```
+
+## Project Structure
+
+```
+PolarisShu/
+├── backend/                    # Rust backend service
+│   ├── src/
+│   │   └── main.rs            # Main application with all logic
+│   ├── Cargo.toml             # Rust dependencies
+│   ├── rustfmt.toml           # Code formatting config
+│   └── .clippy.toml           # Linting config
+│
+├── frontend/                   # React frontend application
+│   ├── src/
+│   │   ├── components/        # React components
+│   │   │   ├── UserList.tsx
+│   │   │   └── ErrorBoundary.tsx
+│   │   ├── services/          # API service layer
+│   │   │   └── api.ts
+│   │   ├── assets/            # Static assets
+│   │   ├── App.tsx            # Main app component
+│   │   ├── main.tsx           # Entry point
+│   │   └── index.css          # Global styles
+│   ├── public/                # Public assets
+│   ├── package.json           # Frontend dependencies
+│   ├── vite.config.ts         # Vite configuration
+│   ├── tailwind.config.js     # Tailwind CSS config
+│   ├── tsconfig.json          # TypeScript config
+│   ├── eslint.config.js       # ESLint config
+│   └── .prettierrc            # Prettier config
+│
+├── scripts/                    # Build and dev scripts
+│   ├── dev.ts                 # Development environment script
+│   └── build.ts               # Production build script
+│
+├── docs/                       # Documentation
+│   └── ARCHITECTURE.md        # This file
+│
+├── README.md                   # Project readme
+├── CONTRIBUTING.md             # Contribution guidelines
+├── CODE_OF_CONDUCT.md          # Code of conduct
+├── LICENSE                     # MIT License
+├── package.json                # Root project config
+└── .gitignore                  # Git ignore rules
+```
+
+## Data Flow
+
+### 1. Health Check Flow
+```
+User → Frontend App → GET /api/health
+                         ↓
+                    Backend Handler
+                         ↓
+                    Returns: {status, version, timestamp}
+                         ↓
+                    Frontend Updates UI
+```
+
+### 2. User List Flow
+```
+User → UserList Component → ApiService.getUsers()
+                               ↓
+                          GET /api/users
+                               ↓
+                          Backend Handler
+                               ↓
+                          Returns: User[]
+                               ↓
+                          Frontend Renders List
+```
+
+## Key Design Decisions
+
+### Backend
+
+1. **Monolithic Structure**: Currently, all backend code is in `main.rs`. As the project grows, consider splitting into modules:
+   - `handlers/` - Endpoint handlers
+   - `models/` - Data models
+   - `middleware/` - Custom middleware
+   - `config/` - Configuration management
+
+2. **Error Handling**: Uses Rust's Result type for error propagation. Future: implement custom error types with thiserror.
+
+3. **CORS Configuration**: Configured to allow localhost:5173 (Vite dev server). In production, update to allow production domain.
+
+4. **Logging**: Uses `tracing` crate with environment-based log levels (default: info).
+
+5. **API Documentation**: Auto-generated from code using Salvo's OpenAPI support.
+
+### Frontend
+
+1. **Error Boundaries**: Implemented to catch and display React errors gracefully.
+
+2. **API Service Layer**: Centralized API calls in `services/api.ts` for better maintainability.
+
+3. **Type Safety**: TypeScript strict mode enabled for maximum type safety.
+
+4. **State Management**: Currently uses React hooks (useState, useEffect). For complex state, consider Redux or Zustand.
+
+5. **Styling**: Tailwind CSS for utility-first styling approach.
+
+## Communication Patterns
+
+### API Communication
+- **Protocol**: HTTP/1.1
+- **Data Format**: JSON
+- **Error Handling**: HTTP status codes + error messages
+- **CORS**: Enabled for development (localhost:5173)
+
+### Development Proxy
+Vite dev server proxies `/api/*` requests to `localhost:8080` to avoid CORS issues during development.
+
+## Security Considerations
+
+1. **CORS**: Properly configured but needs production domain update
+2. **Input Validation**: TODO - Add request validation
+3. **Authentication**: TODO - Implement JWT or session-based auth
+4. **Rate Limiting**: TODO - Add rate limiting middleware
+5. **HTTPS**: TODO - Configure TLS for production
+
+## Performance Considerations
+
+1. **Backend**:
+   - Async I/O with Tokio for high concurrency
+   - Minimal allocations with Rust's zero-cost abstractions
+   - TODO: Add database connection pooling
+
+2. **Frontend**:
+   - Code splitting with Vite
+   - Lazy loading components
+   - TODO: Implement virtual scrolling for large lists
+   - TODO: Add service worker for offline support
+
+## Future Architecture Plans
+
+### Backend
+- [ ] Add database layer (PostgreSQL or SQLite)
+- [ ] Implement repository pattern
+- [ ] Add caching layer (Redis)
+- [ ] Implement authentication/authorization
+- [ ] Add background job processing
+- [ ] Implement rate limiting
+- [ ] Add request validation middleware
+
+### Frontend
+- [ ] Implement routing (React Router)
+- [ ] Add state management (Redux/Zustand)
+- [ ] Implement real-time updates (WebSocket)
+- [ ] Add offline support (Service Worker)
+- [ ] Implement infinite scroll
+- [ ] Add search and filtering
+- [ ] Implement internationalization (i18n)
+
+### DevOps
+- [ ] Add Docker support
+- [ ] Implement CI/CD pipeline
+- [ ] Add automated testing
+- [ ] Set up monitoring and logging
+- [ ] Implement blue-green deployment
+
+## Deployment Strategy
+
+### Development
+```bash
+bun run dev    # Starts both frontend and backend
+```
+
+### Production
+```bash
+# Backend
+cd backend && cargo build --release
+./target/release/backend
+
+# Frontend
+cd frontend && npm run build
+# Serve dist/ with nginx or static server
+```
+
+### Recommended Production Setup
+```
+┌─────────────┐
+│   Nginx     │  Reverse Proxy
+│   (443)     │  SSL Termination
+└──────┬──────┘
+       │
+       ├─────────┐
+       │         │
+   Frontend   Backend
+   (Static)   (8080)
+```
+
+## Testing Strategy
+
+### Backend (TODO)
+- Unit tests: `cargo test`
+- Integration tests: API endpoint tests
+- Load testing: k6 or vegeta
+
+### Frontend (TODO)
+- Unit tests: Vitest
+- Component tests: React Testing Library
+- E2E tests: Playwright or Cypress
+
+## Monitoring and Observability
+
+### Logging
+- Backend: `tracing` crate with structured logging
+- Frontend: Browser console + error reporting
+
+### Metrics (TODO)
+- Request latency
+- Error rates
+- Active users
+- API endpoint usage
+
+### Tracing (TODO)
+- Distributed tracing with OpenTelemetry
+- Request flow visualization
+
+## Contributing
+
+See [CONTRIBUTING.md](../CONTRIBUTING.md) for development workflow and coding standards.
+
+## License
+
+MIT License - See [LICENSE](../LICENSE) for details.

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+- **Documentation**:
+  - Comprehensive README with project details, setup instructions, and development workflow
+  - CONTRIBUTING.md with contribution guidelines and coding standards
+  - CODE_OF_CONDUCT.md for community guidelines
+  - MIT LICENSE file
+  - ARCHITECTURE.md with detailed system architecture documentation
+  - CHANGELOG.md for tracking project changes
+
+- **Backend**:
+  - Health check endpoint at `/api/health` returning status, version, and timestamp
+  - CORS middleware with configurable origin (via `CORS_ALLOWED_ORIGIN` env var)
+  - Structured logging with tracing crate and environment-based log levels
+  - Enhanced API documentation with OpenAPI 3.1
+  - Code formatting configuration (rustfmt.toml)
+  - Linting configuration (.clippy.toml)
+  - Environment variable documentation (.env.example)
+  - Proper error handling and request logging
+
+- **Frontend**:
+  - ErrorBoundary component for graceful error handling
+  - Environment variable documentation (.env.example)
+  - Code formatting configuration (.prettierrc)
+  - Type-safe User interface in API service
+  - Health check integration in status checking
+
+### Changed
+- **Backend**:
+  - Enhanced code organization with comprehensive documentation
+  - Improved error handling and logging throughout
+  - Updated API title to "PolarisShu Backend API"
+  - Made CORS origin configurable via environment variable
+
+- **Frontend**:
+  - Updated API service to use dedicated health check endpoint
+  - Improved type safety by defining User interface locally
+  - Enhanced error handling with ErrorBoundary wrapper
+
+### Fixed
+- TypeScript build errors in frontend components
+- Proper type imports in ErrorBoundary component
+- CORS configuration now supports multiple environments
+
+### Security
+- CORS properly configured with environment-based origins
+- TypeScript strict mode enabled for maximum type safety
+- No vulnerabilities found in npm audit
+
+## [0.1.0] - 2025-12-29
+
+### Added
+- Initial project setup with Rust backend (Salvo framework)
+- React frontend with TypeScript and Tailwind CSS
+- User list API endpoint
+- OpenAPI documentation with Swagger UI
+- Development and build scripts
+- Basic project structure and configuration
+
+[Unreleased]: https://github.com/nkanf-dev/PolarisShu/compare/v0.1.0...HEAD
+[0.1.0]: https://github.com/nkanf-dev/PolarisShu/releases/tag/v0.1.0