simple.go

package service

import (
	"fmt"
	"log"

	"mocking/database"
)

type registerationPreChecker interface {
	UserExists(string) bool
}

type regPreCheck struct {}

func (regPreCheck) UserExists(email string) bool {
	return database.UserExists(email)
}

type User struct {
	Name     string `json:"name"`
	Email    string `json:"email"`
	UserName string `json:"user_name"`
}

func NewRegistrationPreChecker() registerationPreChecker {
	return regPreCheck{}
}

// Register a user if they don't exist
func RegisterUser(user User, regPreCond registerationPreChecker) error {
	// check if user is already registered
	found := regPreCond.UserExists(user.Email)
	if found {
		return fmt.Errorf("email '%s' already registered", user.Email)
	}
	// carry business logic and register the user in the system
	log.Println(user)
	return nil
}