kubilaycicek/CombinatorDesignPattern

Combinator Design Pattern

Before Combinator Design Pattern

public class CustomerValidatorService {
 private boolean isEmailValid(String email) {
     return email.contains("@");
 }

 private boolean isPhoneNumberValid(String phoneNumber) {
     return phoneNumber.startsWith("+0");
 }

 private boolean isAdult(LocalDate dob) {
     return Period.between(dob, LocalDate.now()).getYears() > 18;
 }

 public boolean isValid(Customer customer) {
      return isEmailValid(customer.getEmail()) &&
             isPhoneNumberValid(customer.getPhoneNumber()) &&
             isAdult(customer.getDob());
 }
}

After Combinator Design Pattern

 public interface CustomerRegistrationValidator
     extends Function<Customer, CustomerRegistrationValidator.ValidationResult> {

 static CustomerRegistrationValidator isEmailValid() {
     return customer -> customer.getEmail().contains("@") ?
             ValidationResult.SUCCESS : ValidationResult.EMAIL_NOT_VALID;
 }

 static CustomerRegistrationValidator isPhoneNumberValid() {
     return customer -> customer.getPhoneNumber().startsWith("+0") ?
             ValidationResult.SUCCESS : ValidationResult.PHONE_NUMBER_NOT_VALID;
 }

 static CustomerRegistrationValidator isAdult() {
     return customer -> Period.between(customer.getDob(), LocalDate.now()).getYears() > 18 ?
             ValidationResult.SUCCESS : ValidationResult.IS_NOT_AND_ADULT;
 }

 default CustomerRegistrationValidator and(CustomerRegistrationValidator other) {
     return customer -> {
         ValidationResult result = this.apply(customer);
         return result.equals(ValidationResult.SUCCESS) ? other.apply(customer) : result;
     };
 }

 enum ValidationResult {
     SUCCESS,
     PHONE_NUMBER_NOT_VALID,
     EMAIL_NOT_VALID,
     IS_NOT_AND_ADULT
 }
}