User service example

user.go

package user

import "errors"

type VerifiedID string

type IDService interface {
	VerifyID(id string) (error, VerifiedId)
}

type NewUser struct {
	Username string
	Password string

	IDNumber string
}

type CheckedUserName string

type Login struct {
	Username string
	Password string
}

type CheckedLogin struct {
	CheckedUserName CheckedUserName
	Password string
}

type VerifiedUser struct {
	checkedLogin CheckedLogin
	verifiedId VerifiedID
}

type SavedUser struct {
	VerifiedUser VerifiedUser
}

type UserRepository interface {
	CheckUsername(username string) (error, CheckedUserName)
	SaveUser(verifiedUser VerifiedUser) (error, SavedUser)
}

type UserService struct {
	IDService IDService
	Users UserRepository
}

func CheckUserLogin(userName string, password string) (error, Login) {
	if userName == "" || password == "" {
		return errors.New("username or password is empty"), null
	}
	return (nil, Login{userName, password})
}
	
func (s UserService) RegisterUser(newUser NewUser) (error, SavedUser) {
	// Business validation
	err, login := CheckUserLogin(newUser.Username, newUser.Password)
	if err != nil {
		return err
	}

	// Validate there is no such username
	err, checkedUserName := s.Users.CheckUsername(login.Username)
	if err != nil {
		return err
	}
	
	checkedLogin := CheckedLogin{checkedUserName, login.password}

	// Call an external (government?) service to verify the ID number
	err, verifiedID := s.IDService.VerifyID(newUser.IDNumber)
	if err != nil {
		return err
	}
	
	verifiedUser := VerifiedUser{checkedLogin, verifiedID}

	// Save the user in the persistent store
	err, savedUser := s.Users.SaveUser(verifiedUser)
	if err != nil {
		return err
	}

	return (nil, savedUser)
}