interface UserRegistrationService {
    void isEmailAlreadyUsed(String email);
}

interface PasswordHashService {
    String hash(String plainTextPassword);
}

class User {
    private String email;
    private String passwordHash;

    private User(String email, String passwordHash) {
        this.email = email;
        this.passwordHash = passwordHash;
    }

    public static User registerNew(
        String email,
        String passwordInPlainText,
        UserRegistrationService userRegistrationService,
        PasswordHashService passwordHashService
    ) {
        if (userRegistrationService.isEmailAlreadyUsed(email) {
            throw new DomainException(...);
        }

        return new User(email, passwordHashService.hash(passwordInPlainText));
    }
}

class RegisterNewUserCommand {
    public String email;
    public String passwordInPlainText;
}

class RegisterNewUserCommandHandler {
    private UserRegistrationService userRegistrationService;
    private PasswordHashService passwordHashService;
    private UserRepository userRepository;

    public RegisterNewUserCommandHandler(
        UserRegistrationService userRegistrationService,
        PasswordHashService passwordHashService,
        UserRepository userRepository
    ) {
        this.userRegistrationService = userRegistrationService;
        this.passwordHashService = passwordHashService;
        this.userRepository = userRepository;
    }

    public void handle(RegisterNewUserCommand command) {
        User registeredUser = User.registerNew(
            command.email,
            command.passwordInPlainText,
            userRegistrationService,
            passwordHashService
        );

        userRepository.save(registeredUser);
    }
}