public class UserService {

    private EventStore repository;

    public UserService(EventStore repository) {

        this.repository = repository;

    }

​

    public void createUser(String userId, String firstName, String lastName) {

        repository.addEvent(userId, new UserCreatedEvent(userId, firstName, lastName));

    }

​

    public void updateUser(String userId, Set<Contact> contacts, Set<Address> addresses) {

        User user = UserUtility.recreateUserState(repository, userId);

        user.getContacts().stream()

          .filter(c -> !contacts.contains(c))

          .forEach(c -> repository.addEvent(

            userId, new UserContactRemovedEvent(c.getType(), c.getDetail())));

        contacts.stream()

          .filter(c -> !user.getContacts().contains(c))

          .forEach(c -> repository.addEvent(

            userId, new UserContactAddedEvent(c.getType(), c.getDetail())));

        user.getAddresses().stream()

          .filter(a -> !addresses.contains(a))

          .forEach(a -> repository.addEvent(

            userId, new UserAddressRemovedEvent(a.getCity(), a.getState(), a.getPostcode())));

        addresses.stream()

          .filter(a -> !user.getAddresses().contains(a))

          .forEach(a -> repository.addEvent(

            userId, new UserAddressAddedEvent(a.getCity(), a.getState(), a.getPostcode())));

    }

​

    public Set<Contact> getContactByType(String userId, String contactType) {

        User user = UserUtility.recreateUserState(repository, userId);

        return user.getContacts().stream()

          .filter(c -> c.getType().equals(contactType))

          .collect(Collectors.toSet());

    }

​

    public Set<Address> getAddressByRegion(String userId, String state) throws Exception {

        User user = UserUtility.recreateUserState(repository, userId);

        return user.getAddresses().stream()

          .filter(a -> a.getState().equals(state))

          .collect(Collectors.toSet());

    }

}

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