template/cmd/app/config.go

package main

import (
	"flag"
)

// Config is the root configuration object. Add sub-structs as the app grows.
type Config struct {
	App     AppConfig
	Logger  LoggerConfig
	Greeter GreeterConfig
}

// AppConfig holds generic application settings.
type AppConfig struct {
	Port int
	Env  string // dev | staging | prod
}

// LoggerConfig controls logging behavior.
type LoggerConfig struct {
	Level     string // debug | info | warn | error
	DebugFile string // non-empty enables debug mode: writes full JSON trace to this path
}

// Greeter config for internal/greeter/Service.
type GreeterConfig struct {
	Name string
}

// parseArgs parses application configuration from command-line flags.
// Defaults are defined here; override at runtime with flags:
//
//	./app -port 9090 -env prod -log-level warn 2 > log.log
//
// Usage:
//
//	cfg := config.parseArgs()
//	fmt.Println(cfg.App.Port)
func parseArgs() *Config {
	name := flag.String("name", "Gopher", "application name")
	port := flag.Int("port", 8080, "listen port")
	env := flag.String("env", "dev", "environment: dev | staging | prod")
	level := flag.String("log-level", "info", "log level: debug | info | warn | error")
	debugLog := flag.String("debug-log", "", "write full debug trace to file (enables debug mode)")

	flag.Parse()

	return &Config{
		App: AppConfig{
			Port: *port,
			Env:  *env,
		},
		Logger: LoggerConfig{
			Level:     *level,
			DebugFile: *debugLog,
		},
		Greeter: GreeterConfig{
			Name: *name,
		},
	}
}