Rewrite Go Backend with Clean Architecture and Modern Best Practices

[Copilot]

This PR completely rewrites the Go portion of the pokeserver application, addressing critical issues and implementing modern Go best practices with clean architecture.

Overview

The existing Go backend had several significant issues that made it unreliable and difficult to maintain:

• Poor error handling using log.Fatal throughout the codebase
• Mixed concerns with business logic embedded in HTTP handlers
• Global variables and tight coupling
• No proper configuration management
• Missing graceful shutdown and middleware
• Inconsistent struct definitions causing test failures

This rewrite implements a clean, layered architecture while maintaining 100% backward compatibility with existing API endpoints.

Architecture Changes

Clean Architecture Implementation

┌─────────────────┐
│   HTTP Layer    │  handlers.go, middleware.go, validation.go
├─────────────────┤
│ Business Layer  │  service.go (Pokemon operations)
├─────────────────┤
│   Data Layer    │  repository.go (Database interface)
├─────────────────┤
│ External APIs   │  pokeclient.go (PokeAPI integration)
└─────────────────┘

New Components Added

Configuration Management (config.go)

• Centralized configuration with validation
• Environment variable support with fallbacks
• Type-safe configuration loading

Structured Logging (logger.go)

• JSON-based structured logging using Go's slog
• Context-aware logging with request tracing
• Proper error tracking and field correlation

Middleware System (middleware.go)

• CORS handling (replaces manual header setting)
• Request/response logging with timing
• Panic recovery with graceful error responses
• Chainable middleware pattern

Input Validation (validation.go)

• Comprehensive request parameter validation
• Structured error responses with field-level details
• Type-safe validation functions

Service Layer (service.go)

• Business logic separation from HTTP concerns
• Pokemon operations: get random, vote, list all
• Proper error handling and validation

Key Improvements

Error Handling

Before:

if err != nil {
    log.Fatal(err)  // Crashes entire application
}

After:

if err != nil {
    logger.WithError(err).Error("Operation failed")
    return fmt.Errorf("operation failed: %w", err)
}

HTTP Responses

Before:

http.Error(w, "Error", 500)  // Plain text, no structure

After:

WriteErrorResponse(w, http.StatusBadRequest, "validation_error", 
    "Invalid parameters", validationDetails)
// Returns structured JSON with error codes and details

Dependency Injection

Before:

var repo *Repository  // Global variable

After:

type Handlers struct {
    pokemonService *PokemonService
    logger         *Logger
}
// Constructor injection with interfaces

Graceful Shutdown

Added proper signal handling with timeout-based graceful shutdown:

quit := make(chan os.Signal, 1)
signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
<-quit

ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
server.Shutdown(ctx)

API Enhancements

All existing endpoints remain unchanged but now include:

• Proper HTTP method validation
• Structured JSON error responses
• Input validation with detailed error messages
• Consistent response formats

New Health Check Endpoint

GET /health
{
  "status": "healthy"
}

Enhanced Error Responses

{
  "error": "validation_error",
  "message": "Invalid request parameters",
  "details": [
    {
      "field": "vote",
      "message": "vote direction must be 'up' or 'down'"
    }
  ]
}

Testing Improvements

• Fixed Pokemon struct inconsistencies that caused test failures
• Added proper dependency injection in test setup
• Maintained all existing test functionality
• Enhanced error logging in tests

Configuration

The application now supports flexible configuration:

Environment Variables:

• DATABASE_URL
• PORT
• POKEAPI_URL
• POKEAPI_MAX

Configuration File (.env.example):

database:
  url: "postgres://user:password@localhost:5432/pokemon"
server:
  port: "8080"
pokeapi:
  url: "https://pokeapi.co/api/v2/pokemon?limit="
  max: 1025

Migration Notes

This rewrite is completely backward compatible. All existing API clients will continue to work without any changes, but will now benefit from:

• Improved reliability (no more application crashes)
• Better error messages
• Faster response times
• Production-ready error handling

Documentation

Added comprehensive documentation including:

• Architecture overview and design decisions
• API endpoint documentation with examples
• Configuration options and environment setup
• Go doc comments for all public APIs

The codebase is now production-ready with proper error handling, monitoring capabilities, and maintainable architecture while preserving all existing functionality.

This pull request was created as a result of the following prompt from Copilot chat.

Rewrite Go Backend for Pokeserver

Overview

Completely rewrite the Go portion of the pokeserver application with improved architecture, better error handling, and modern Go practices.

Current Issues to Address

1. Poor error handling - Many functions use log.Fatal instead of proper error propagation
2. Lack of separation of concerns - Business logic mixed with HTTP handlers
3. No proper configuration management - Configuration scattered throughout the code
4. Missing dependency injection - Global variables used for repository access
5. Inconsistent struct definitions - Pokemon struct definition issues in tests
6. No proper logging - Using basic log package without structured logging
7. Missing graceful shutdown - Server doesn't handle shutdown signals
8. No middleware - CORS and other cross-cutting concerns handled manually
9. Poor test organization - Tests mixed with production code structure

Requirements for Rewrite

1. Clean Architecture - Separate handlers, services, and repository layers
2. Proper Error Handling - Use error returns instead of panics/fatal logs
3. Dependency Injection - Remove global variables and use proper DI
4. Configuration Management - Centralized config with validation
5. Structured Logging - Use structured logging with levels
6. Middleware Support - CORS, logging, and other middleware
7. Graceful Shutdown - Handle OS signals for clean shutdown
8. Input Validation - Validate all incoming requests
9. Better Testing - Improved test structure and coverage
10. Documentation - Add proper Go doc comments

Technical Improvements

• Use context properly throughout the application
• Implement proper HTTP status codes and error responses
• Add request/response validation
• Improve database connection management
• Add health check endpoints
• Use interfaces for better testability
• Follow Go project layout standards

Files to Rewrite

• go/pokeserver.go - Main application entry point
• go/handlers.go - HTTP handlers with proper separation
• go/repository.go - Database layer with interfaces
• go/pokemon.go - Domain models and types
• go/pokeclient.go - External API client
• Add new files for services, middleware, config, etc.
• Update tests to match new structure

The rewrite should maintain backward compatibility for the API endpoints while significantly improving the internal code quality and maintainability.

---

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Name	Status	Preview	Comments	Updated (UTC)
pokeserver	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 27, 2025 6:01am