source: voting/src/main/java/geniusweb/voting/votingevaluators/LargestAgreement.java@ 52

package geniusweb.voting.votingevaluators;

import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnore;

import geniusweb.actions.PartyId;
import geniusweb.inform.Agreements;
import geniusweb.issuevalue.Bid;
import geniusweb.voting.CollectedVotes;
import geniusweb.voting.VotingEvaluator;

/**
 * Take the first possible agreement, and take the largest possible agreement.
 * Stop after first agreement.
 */
public class LargestAgreement implements VotingEvaluator {
        @JsonIgnore
        private final CollectedVotes allVotes;

        // caching
        @JsonIgnore
        private Agreements maxAgreements = null;

        @JsonCreator
        public LargestAgreement() {
                this(new CollectedVotes(Collections.emptyMap(),
                                Collections.emptyMap()));
        }

        protected LargestAgreement(CollectedVotes votes) {
                this.allVotes = votes;
        }

        @Override
        public Agreements getAgreements() {
                if (maxAgreements == null)
                        maxAgreements = collectVotes();
                return maxAgreements;
        }

        @Override
        public boolean isFinished() {
                HashSet<PartyId> parties = new HashSet<PartyId>(
                                allVotes.getVotes().keySet());
                parties.removeAll(getAgreements().getMap().keySet());
                return parties.size() < 2;
        }

        @Override
        public VotingEvaluator create(CollectedVotes votes) {
                return new LargestAgreement(votes);
        }

        /**
         * @return the agreements that were reached from the given votes, using the
         *         greedy algorithm picking the largets votesets.
         */
        protected Agreements collectVotes() {
                Agreements agreement = new Agreements();

                Map<Bid, Set<PartyId>> agrees = allVotes.getMaxAgreements();
                if (agrees.isEmpty())
                        return agreement;// none

                // find the one with max group power
                Bid maxbid = agrees.keySet().stream().max(Comparator
                                .comparingInt(bid -> allVotes.getTotalPower(agrees.get(bid))))
                                .get();
                agreement = agreement.with(new Agreements(maxbid, agrees.get(maxbid)));
                return agreement;
        }

        @Override
        public int hashCode() {
                final int prime = 31;
                int result = 1;
                result = prime * result
                                + ((allVotes == null) ? 0 : allVotes.hashCode());
                return result;
        }

        @Override
        public boolean equals(Object obj) {
                if (this == obj)
                        return true;
                if (obj == null)
                        return false;
                if (getClass() != obj.getClass())
                        return false;
                LargestAgreement other = (LargestAgreement) obj;
                if (allVotes == null) {
                        if (other.allVotes != null)
                                return false;
                } else if (!allVotes.equals(other.allVotes))
                        return false;
                return true;
        }

        @Override
        public String toString() {
                return "LargestAgreement";
        }
}