Configuration, project structure and graceful shutdown

type Config struct {
	Port        string
	DatabaseURL string
	LogLevel    slog.Level
}

func loadConfig() (Config, error) {
	cfg := Config{Port: "8080", LogLevel: slog.LevelInfo}
	if v := os.Getenv("PORT"); v != "" {
		cfg.Port = v
	}
	cfg.DatabaseURL = os.Getenv("DATABASE_URL")
	if cfg.DatabaseURL == "" {
		return cfg, errors.New("DATABASE_URL is required")
	}
	if os.Getenv("LOG_LEVEL") == "debug" {
		cfg.LogLevel = slog.LevelDebug
	}
	return cfg, nil
}

expense-api/
├── go.mod
├── main.go               config, logger, DB, server, shutdown (wiring only)
├── internal/
│   ├── expense/          types, validation, business rules (no HTTP, no SQL)
│   ├── store/            PGStore: SQL queries (implements the Store interface)
│   └── httpapi/          handlers, middleware, routes, JSON helpers
├── migrations/           001_create_expenses.sql ...
├── Dockerfile
└── README.md

func main() {
	cfg, err := loadConfig()
	if err != nil {
		slog.Error("config", "err", err)
		os.Exit(1)
	}

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	db, err := openDB(ctx, cfg.DatabaseURL)
	if err != nil {
		slog.Error("database", "err", err)
		os.Exit(1)
	}
	defer db.Close()

	srv := &http.Server{
		Addr:              ":" + cfg.Port,
		Handler:           httpapi.New(store.NewPG(db)),
		ReadHeaderTimeout: 5 * time.Second,
	}

	go func() {
		slog.Info("listening", "port", cfg.Port)
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			slog.Error("server", "err", err)
			stop() // trigger shutdown
		}
	}()

	<-ctx.Done() // wait for Ctrl+C or SIGTERM
	slog.Info("shutting down")

	shutdownCtx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()
	if err := srv.Shutdown(shutdownCtx); err != nil {
		slog.Error("shutdown", "err", err)
	}
	slog.Info("bye")
}