cv-site/doc/ARCHITECTURE.md

# Architecture Documentation

## Overview

This CV website is built following Go best practices with a focus on:
- **Simplicity**: Clean, readable code
- **Maintainability**: Well-structured packages
- **Reliability**: Proper error handling and logging
- **Performance**: Efficient template caching
- **Security**: Multiple layers of protection

## Architecture Patterns

### 1. Package Structure (Internal Directory Pattern)

```
cv/
├── main.go                    # Application entry point
└── internal/                  # Private packages (cannot be imported by other projects)
    ├── config/               # Configuration management
    ├── handlers/             # HTTP request handlers
    ├── middleware/           # HTTP middleware
    ├── models/               # Data models and business logic
    └── templates/            # Template management
```

**Benefits**:
- Clear separation of concerns
- Encapsulation (internal packages cannot be imported externally)
- Easy to test and maintain
- Scalable structure

### 2. Dependency Injection

Handlers and services receive their dependencies through constructors:

```go
// ✅ Good: Dependencies injected
type CVHandler struct {
    templates *templates.Manager
}

func NewCVHandler(tmpl *templates.Manager) *CVHandler {
    return &CVHandler{templates: tmpl}
}

// ❌ Bad: Global state
var globalTemplates *template.Template
```

**Benefits**:
- Testability (easy to mock dependencies)
- Flexibility (swap implementations)
- Explicit dependencies

### 3. Error Handling Strategy

Three-tier error handling:

```go
// 1. Domain errors (AppError)
type AppError struct {
    Err        error   // Original error
    Message    string  // User-friendly message
    StatusCode int     // HTTP status
    Internal   bool    // Hide details from client
}

// 2. Error constructors for common cases
NotFoundError("Resource not found")
BadRequestError("Invalid input")
InternalError(err)

// 3. Centralized error handler
HandleError(w, r, err)
```

**Benefits**:
- Consistent error responses
- Proper logging
- Security (internal errors hidden)
- Client-specific responses (JSON, HTML, HTMX)

### 4. Middleware Chain

Onion-like middleware wrapping:

```
Request → Recovery → Logger → Security → Handler → Response
          ↑         ↑         ↑          ↑
          Panics    Logging   Headers   Business Logic
```

**Implementation**:
```go
handler := middleware.Recovery(
    middleware.Logger(
        middleware.SecurityHeaders(mux),
    ),
)
```

**Benefits**:
- Separation of cross-cutting concerns
- Reusable components
- Easy to add/remove middleware
- Predictable request flow

## Component Details

### Configuration Management (`internal/config`)

**Pattern**: Environment-based configuration with sensible defaults

```go
cfg := config.Load()  // Reads from env vars
cfg.Server.Port       // Defaults to "1999"
cfg.Template.HotReload // Auto-detects development mode
```

**Features**:
- Environment variable support
- Type-safe configuration
- Development/production modes
- Sensible defaults

### Template Management (`internal/templates`)

**Pattern**: Template manager with hot-reload support

```go
manager := templates.NewManager(cfg)
manager.Render("index.html")  // Hot-reloads in dev mode
```

**Features**:
- Centralized template loading
- Custom template functions
- Hot-reload in development
- Thread-safe caching
- Graceful error handling

### HTTP Handlers (`internal/handlers`)

**Pattern**: Handler structs with methods

```go
type CVHandler struct {
    templates *templates.Manager
}

func (h *CVHandler) Home(w http.ResponseWriter, r *http.Request)
func (h *CVHandler) CVContent(w http.ResponseWriter, r *http.Request)
```

**Features**:
- Clean separation of routes
- Dependency injection
- Consistent error handling
- HTMX-aware responses

### Middleware (`internal/middleware`)

**Components**:
1. **Recovery**: Catches panics, logs stack traces
2. **Logger**: Structured request/response logging
3. **SecurityHeaders**: CSP, XSS protection, clickjacking prevention

## Security Features

### 1. Security Headers

```go
X-Frame-Options: SAMEORIGIN              // Prevent clickjacking
X-Content-Type-Options: nosniff          // Prevent MIME sniffing
X-XSS-Protection: 1; mode=block          // XSS protection
Content-Security-Policy: ...             // Restrict resource loading
Referrer-Policy: strict-origin-...       // Control referrer info
```

### 2. Request Timeouts

```go
server := &http.Server{
    ReadTimeout:  15 * time.Second,  // Prevent slow clients
    WriteTimeout: 15 * time.Second,  // Prevent slow responses
    IdleTimeout:  120 * time.Second, // Keep-alive timeout
}
```

### 3. Error Information Hiding

```go
appErr := NewAppError(err, "Database error", 500, true)
// Client sees: "Internal Server Error"
// Logs show: actual error details
```

## Performance Optimizations

### 1. Template Caching

```go
// Templates parsed once at startup
templates := template.New("").ParseGlob("*.html")

// Hot-reload only in development
if cfg.Template.HotReload {
    templates.ParseGlob("*.html")  // Re-parse on each request
}
```

### 2. Static File Caching

```go
// Development: 1 hour cache
// Production: 1 day cache
Cache-Control: public, max-age=86400
```

### 3. HTTP/2 Support

Go's `http.Server` automatically supports HTTP/2 when using HTTPS.

## Graceful Shutdown

```go
// 1. Listen for signals
shutdown := make(chan os.Signal, 1)
signal.Notify(shutdown, os.Interrupt, syscall.SIGTERM)

// 2. Shutdown with timeout
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
server.Shutdown(ctx)
```

**Features**:
- Finish in-flight requests
- 30-second grace period
- Forced shutdown if timeout exceeded

## HTMX Integration Patterns

### 1. Partial Content Rendering

```go
// Full page: /
// Partial: /cv?lang=es (returns only content div)

if r.Header.Get("HX-Request") != "" {
    // HTMX request - return partial
    renderPartial()
} else {
    // Regular request - return full page
    renderFull()
}
```

### 2. Language Switching

```html
<button hx-get="/cv?lang=es"
        hx-target="#cv-content"
        hx-swap="innerHTML">
    🇪🇸 Español
</button>
```

**Benefits**:
- No JavaScript frameworks needed
- Progressive enhancement
- Server-rendered content
- Better SEO

## Testing Strategy

### Manual Testing

```bash
# 1. Health check
curl http://localhost:1999/health

# 2. Happy path
curl "http://localhost:1999/?lang=en"

# 3. Error cases
curl "http://localhost:1999/?lang=invalid"  # 400 Bad Request

# 4. HTMX requests
curl -H "HX-Request: true" "http://localhost:1999/cv?lang=es"

# 5. Security headers
curl -I http://localhost:1999/
```

### Future: Automated Tests

```go
func TestCVHandler_Home(t *testing.T) {
    // Setup
    cfg := &config.TemplateConfig{Dir: "../../templates"}
    tmpl, _ := templates.NewManager(cfg)
    handler := handlers.NewCVHandler(tmpl)

    // Execute
    req := httptest.NewRequest("GET", "/?lang=en", nil)
    w := httptest.NewRecorder()
    handler.Home(w, req)

    // Assert
    assert.Equal(t, 200, w.Code)
}
```

## Deployment Options

### 1. Standalone Binary

```bash
go build -o cv-server -ldflags="-s -w" .
./cv-server
```

### 2. Docker

```bash
docker build -t cv-server .
docker run -p 1999:1999 cv-server
```

### 3. Cloud Platforms

**Recommended**:
- **Fly.io**: `fly launch` (auto-detects Dockerfile)
- **Railway**: Connect GitHub, auto-deploy
- **Google Cloud Run**: Serverless containers
- **AWS ECS/Fargate**: Container orchestration

## Best Practices Applied

1. ✅ **Standard Project Layout**: Internal packages, clear structure
2. ✅ **Error Handling**: Custom error types, consistent handling
3. ✅ **Logging**: Structured, informative logs
4. ✅ **Configuration**: Environment-based with defaults
5. ✅ **Security**: Multiple layers of protection
6. ✅ **Graceful Shutdown**: Clean service termination
7. ✅ **Dependency Injection**: Testable, maintainable code
8. ✅ **Middleware Pattern**: Separation of concerns
9. ✅ **Template Management**: Efficient, cached rendering
10. ✅ **Production-Ready**: Timeouts, health checks, monitoring hooks

## Scaling Considerations

### Current State: Single Instance
- Perfect for CV website (low traffic)
- ~1000s of requests/second capability
- Minimal resource usage

### Future: Multi-Instance (if needed)
1. **Load Balancer**: nginx, Caddy, or cloud LB
2. **Shared Storage**: For static files (S3, Cloud Storage)
3. **Health Checks**: `/health` endpoint already implemented
4. **Metrics**: Add Prometheus metrics
5. **Caching**: Redis for template cache (if very high traffic)

## Monitoring & Observability

### Current Implementation
- **Structured Logging**: Request/response logging
- **Health Check**: `/health` endpoint
- **Error Tracking**: Detailed error logs with stack traces

### Future Enhancements
```go
// Metrics
prometheus.InstrumentHandler("/", handler)

// Distributed Tracing
opentelemetry.Trace(handler)

// Error Monitoring
sentry.CaptureException(err)
```

## Conclusion

This architecture provides:
- ✅ Clean, maintainable code
- ✅ Production-ready error handling
- ✅ Security best practices
- ✅ Performance optimizations
- ✅ Easy deployment options
- ✅ Room for future growth

Perfect for a professional CV website with potential to scale.