gistfile1.go

package main

import (
	"fmt"
)

type Service struct {
	ErrorLevel int
	AWSKey     string
	AWSSecret  string
	AfterHook  func()
}

func (s *Service) Config(opts ...option) {
	for _, opt := range opts {
		opt(s)
	}
}

type option func(*Service)

const (
	DEBUG = iota
	INFO
	WARN
	FATAL
	PANIC
)

func LogLevel(level int) option {
	return func(s *Service) {
		s.ErrorLevel = level
	}
}

func AfterComplete(f func()) option {
	return func(s *Service) {
		s.AfterHook = f
	}
}

type S3 struct {
	Key    string
	Secret string
}

func Backend(opt S3) option {
	return func(s *Service) {
		s.AWSKey = opt.Key
		s.AWSSecret = opt.Secret
	}
}

func ConfigService(s *Service) {
	s.Config(
		LogLevel(WARN),

		Backend(S3{
			Key:    "API_KEY",
			Secret: "SUPER SECRET",
		}),

		AfterComplete(func() {
			fmt.Println("service ready")
		}),
	)
}

func main() {
	s := Service{}
	ConfigService(&s)

	fmt.Printf("%v", s)
}