source: voting/src/main/java/geniusweb/voting/votingevaluators/LargestAgreementsLoop.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;

/**
 * {@link #getAgreements()} collects all possible {@link Agreements}. We're
 * finished only when {@link #getAgreements()} covers all except possibly 1
 * party.
 * 
 * The agreements is a list of {@link Bid}s and a maximum-sized list of
 * {@link PartyId}s that placed a satisfied vote for that bid. maximum-sized
 * means that there is no larger subset of votes for that bid. There may be
 * other subsets of equal size for the bid. If there are no agreements at all
 * for a bid, the bid is not placed in the map.
 * 
 */
public class LargestAgreementsLoop implements VotingEvaluator {
        @JsonIgnore
        private final CollectedVotes allVotes;

        // caching
        @JsonIgnore
        private Agreements maxAgreements = null;

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

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

        @Override
        public Agreements getAgreements() {
                if (maxAgreements == null)
                        maxAgreements = collectAgreements();
                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 LargestAgreementsLoop(votes);
        }

        /**
         * @return the agreements that were reached from the given votes, using the
         *         greedy algorithm picking the largets votesets.
         */
        protected Agreements collectAgreements() {
                CollectedVotes remainingvotes = allVotes;
                Agreements newagreements = new Agreements();
                while (true) {
                        Map<Bid, Set<PartyId>> agrees = remainingvotes.getMaxAgreements();
                        if (agrees.isEmpty())
                                break;
                        // find the bid with max group power
                        Bid maxbid = agrees.keySet().stream()
                                        .max(Comparator.comparingInt(
                                                        bid -> allVotes.getTotalPower(agrees.get(bid))))
                                        .get();
                        Set<PartyId> maxparties = agrees.get(maxbid);
                        newagreements = newagreements
                                        .with(new Agreements(maxbid, maxparties));
                        remainingvotes = remainingvotes.without(maxparties);
                }
                return newagreements;
        }

        /**
         * WARNING you must manually set prime=37 here to fix collision with
         * {@link LargestAgreement}.
         */
        @Override
        public int hashCode() {
                final int prime = 37;
                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;
                LargestAgreementsLoop other = (LargestAgreementsLoop) 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 "LargestAgreementsLoop";
        }
}