io.github.oliviercailloux.j_voting.preferences.classes.MutablePreferenceImpl Maven / Gradle / Ivy

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General classes for dealing with social choice theory.
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package io.github.oliviercailloux.j_voting.preferences.classes;

import java.util.Objects;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.common.graph.GraphBuilder;
import com.google.common.graph.Graphs;
import com.google.common.graph.ImmutableGraph;
import com.google.common.graph.MutableGraph;

import io.github.oliviercailloux.j_voting.Alternative;
import io.github.oliviercailloux.j_voting.Voter;
import io.github.oliviercailloux.j_voting.preferences.MutablePreference;
import io.github.oliviercailloux.j_voting.preferences.Preference;

/**
 * Implements MutablePreference interface.
 *
 * The structure of a MutablePreference is a MutableGraph in which an edge
 * represents the relation "at least as good as".
 *
 * @see io.github.oliviercailloux.j_voting.preferences.Preference
 * @see io.github.oliviercailloux.j_voting.preferences.MutablePreference
 */
public class MutablePreferenceImpl implements MutablePreference {

	protected Voter voter;
	protected MutableGraph graph;
	protected Set alternatives;
	private static final Logger LOGGER = LoggerFactory.getLogger(MutablePreference.class.getName());

	private MutablePreferenceImpl(Voter voter, MutableGraph prefGraph) {
		this.voter = voter;
		graph = prefGraph;
		alternatives = graph.nodes();
	}

	/**
	 * @param pref  is a mutable graph of alternatives representing the preference.
	 *              Each node of the graph contains a set, if this set contains
	 *              several alternatives, it means that those alternatives are
	 *              ex-aequo
	 * @param voter is the Voter associated to the Preference.
	 * @return the mutable preference
	 * @see Voter
	 */
	public static MutablePreference given(Voter voter, MutableGraph pref) {
		LOGGER.debug("MutablePreferenceImpl given");
		Preconditions.checkNotNull(voter);
		Preconditions.checkNotNull(pref);
		return new MutablePreferenceImpl(voter, pref);
	}

	/**
	 * @param voter is the Voter associated to the Preference.
	 * @return a MutablePreference with the same voter and an empty graph
	 */
	public static MutablePreferenceImpl given(Voter voter) {
		LOGGER.debug("MutablePreferenceImpl given with voter");
		Preconditions.checkNotNull(voter);
		MutableGraph pref = GraphBuilder.directed().allowsSelfLoops(true).build();
		return new MutablePreferenceImpl(voter, pref);
	}

	/**
	 * Factory method making new MutablePreference from an other Preference. It
	 * creates a new similar graph instance (mutable). The voter instance of the
	 * created preference is the same as the copied preference.
	 *
	 * @param pref a Preference
	 * @return a copy of this preference as a MutablePreference, with the same
	 *         voter.
	 */
	public static MutablePreferenceImpl given(Preference pref) {
		Preconditions.checkNotNull(pref);
		return new MutablePreferenceImpl(pref.getVoter(), Graphs.copyOf(pref.asGraph()));
	}

	@Override
	public ImmutableGraph asGraph() {
		return ImmutableGraph.copyOf(Graphs.transitiveClosure(graph));
	}

	@Override
	public MutableGraph asMutableGraph() {
		return graph;
	}

	@Override
	public void addAlternative(Alternative alternative) {
		LOGGER.debug("MutablePreferenceImpl addAlternative");
		Preconditions.checkNotNull(alternative);
		graph.addNode(alternative);
	}

	@Override
	public void addEquivalence(Alternative a1, Alternative a2) {
		LOGGER.debug("MutablePreferenceImpl addEquivalence");
		Preconditions.checkNotNull(a1);
		Preconditions.checkNotNull(a2);
		graph.putEdge(a1, a2);
		graph.putEdge(a2, a1);
	}

	@Override
	public void setAsLeastAsGood(Alternative a1, Alternative a2) {
		LOGGER.debug("MutablePreferenceImpl putEdge");
		Preconditions.checkNotNull(a1);
		Preconditions.checkNotNull(a2);
		graph.putEdge(a1, a2);
	}

	/**
	 * @return an immutable set of all alternatives of the preference
	 * 
	 */
	@Override
	public Set getAlternatives() {
		LOGGER.debug("MutablePreferenceImpl getAlternatives");
		if (alternatives.size() == graph.nodes().size() && alternatives.containsAll(graph.nodes())) {
			return ImmutableSet.copyOf(alternatives);
		} else {
			throw new IllegalStateException("Must not remove an alternative from the set");
		}
	}

	@Override
	public Voter getVoter() {
		return voter;
	}

	@Override
	public String toString() {
		return MoreObjects.toStringHelper(this).add("voter", voter).add("graph", graph).toString();
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}
		if (obj == null) {
			return false;
		}
		if (!(obj instanceof MutablePreferenceImpl)) {
			return false;
		}
		MutablePreferenceImpl other = (MutablePreferenceImpl) obj;
		return Objects.equals(voter, other.voter) && Objects.equals(graph, other.graph);
	}
}