import java.util.function.Predicate;

import static java.util.Collections.singletonList;

/**
 * Generic container for conflicts. It's generic so that hopefully it's easier to comprehend (and test).
 */
class ConflictContainer<K, T> {

    final LinkedList<Conflict> conflicts = new LinkedList<>();
    private final Map<K, Conflict> conflictsByParticipant = new HashMap<>();

    private final static Logger LOGGER = Logging.getLogger(DefaultConflictHandler.class);

    private final ModuleConflictResolver<ComponentState> resolver;
    private final ConflictContainer<ModuleIdentifier, ComponentState> conflicts = new ConflictContainer<>();
    private final ModuleReplacementsData moduleReplacements;

    public DefaultConflictHandler(ModuleConflictResolver<ComponentState> resolver, ModuleReplacementsData moduleReplacements) {

import java.util.Set;

class PotentialConflictFactory {

    private static final PotentialConflict NO_CONFLICT = new NoConflict();

    static <T> PotentialConflict potentialConflict(@Nullable final ConflictContainer<ModuleIdentifier, T>.Conflict conflict) {
        if (conflict == null) {
            return NO_CONFLICT;
        }
        return new HasConflict(conflict.participants);
    }

import spock.lang.Specification
import spock.lang.Subject

class ConflictContainerTest extends Specification {

    @Subject container = new ConflictContainer<String, Integer>()

    def "no conflict when candidates are empty"() {
        def conflict = container.newElement('a', [], null)

        expect:
        conflict == null
        container.size == 0
    }