Leadership.java

/*
 * Copyright 2014-present Open Networking Laboratory
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.onosproject.cluster;

import java.util.Objects;
import java.util.List;

import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableList;

/**
 * State of leadership for topic.
 * <p>
 * Provided by this construct is the current {@link Leader leader} and the list of
 * {@link NodeId nodeId}s currently registered as candidates for election for the topic.
 * Keep in mind that only registered candidates can become leaders.
 */
public class Leadership {

    private final String topic;
    private final Leader leader;
    private final List<NodeId> candidates;

    public Leadership(String topic, Leader leader, List<NodeId> candidates) {
        this.topic = topic;
        this.leader = leader;
        this.candidates = ImmutableList.copyOf(candidates);
    }

    /**
     * Returns the leadership topic.
     *
     * @return leadership topic.
     */
    public String topic() {
        return topic;
    }

    /**
     * Returns the {@link NodeId nodeId} of the leader.
     *
     * @return leader node identifier; will be null if there is no leader
     */
    public NodeId leaderNodeId() {
        return leader == null ? null : leader.nodeId();
    }

    /**
     * Returns the leader for this topic.
     *
     * @return leader; will be null if there is no leader for topic
     */
    public Leader leader() {
        return leader;
    }

    /**
     * Returns an preference-ordered list of nodes that are in the leadership
     * race for this topic.
     *
     * @return a list of NodeIds in priority-order, or an empty list.
     */
    public List<NodeId> candidates() {
        return candidates;
    }

    @Override
    public int hashCode() {
        return Objects.hash(topic, leader, candidates);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof Leadership) {
            final Leadership other = (Leadership) obj;
            return Objects.equals(this.topic, other.topic) &&
                    Objects.equals(this.leader, other.leader) &&
                    Objects.equals(this.candidates, other.candidates);
        }
        return false;
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(this.getClass())
            .add("topic", topic)
            .add("leader", leader)
            .add("candidates", candidates)
            .toString();
    }
}