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/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you 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.elasticsearch.discovery.zen.elect;

import com.carrotsearch.hppc.ObjectContainer;
import org.apache.lucene.util.CollectionUtil;
import org.elasticsearch.Version;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.settings.Validator;
import org.elasticsearch.common.component.AbstractComponent;
import org.elasticsearch.common.inject.Inject;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.util.CollectionUtils;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;

/**
 *
 */
public class ElectMasterService extends AbstractComponent {

    public static final String DISCOVERY_ZEN_MINIMUM_MASTER_NODES = "discovery.zen.minimum_master_nodes";
    public static final Validator DISCOVERY_ZEN_MINIMUM_MASTER_NODES_VALIDATOR = new Validator() {
        @Override
        public String validate(String setting, String value, ClusterState clusterState) {
            int intValue;
            try {
                intValue = Integer.parseInt(value);
            } catch (NumberFormatException ex) {
                return "cannot parse value [" + value + "] as an integer";
            }
            int masterNodes = clusterState.nodes().masterNodes().size();
            if (intValue > masterNodes) {
                return "cannot set " + ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES + " to more than the current master nodes count [" + masterNodes + "]";
            }
            return null;
        }
    };

    // This is the minimum version a master needs to be on, otherwise it gets ignored
    // This is based on the minimum compatible version of the current version this node is on
    private final Version minMasterVersion;
    private final NodeComparator nodeComparator = new NodeComparator();

    private volatile int minimumMasterNodes;

    @Inject
    public ElectMasterService(Settings settings, Version version) {
        super(settings);
        this.minMasterVersion = version.minimumCompatibilityVersion();
        this.minimumMasterNodes = settings.getAsInt(DISCOVERY_ZEN_MINIMUM_MASTER_NODES, -1);
        logger.debug("using minimum_master_nodes [{}]", minimumMasterNodes);
    }

    public void minimumMasterNodes(int minimumMasterNodes) {
        this.minimumMasterNodes = minimumMasterNodes;
    }

    public int minimumMasterNodes() {
        return minimumMasterNodes;
    }

    public boolean hasEnoughMasterNodes(Iterable nodes) {
        if (minimumMasterNodes < 1) {
            return true;
        }
        int count = 0;
        for (DiscoveryNode node : nodes) {
            if (node.masterNode()) {
                count++;
            }
        }
        return count >= minimumMasterNodes;
    }

    /**
     * Returns the given nodes sorted by likelyhood of being elected as master, most likely first.
     * Non-master nodes are not removed but are rather put in the end
     */
    public List sortByMasterLikelihood(Iterable nodes) {
        ArrayList sortedNodes = CollectionUtils.iterableAsArrayList(nodes);
        CollectionUtil.introSort(sortedNodes, nodeComparator);
        return sortedNodes;
    }

    /**
     * Returns a list of the next possible masters.
     */
    public DiscoveryNode[] nextPossibleMasters(ObjectContainer nodes, int numberOfPossibleMasters) {
        List sortedNodes = sortedMasterNodes(Arrays.asList(nodes.toArray(DiscoveryNode.class)));
        if (sortedNodes == null) {
            return new DiscoveryNode[0];
        }
        List nextPossibleMasters = new ArrayList<>(numberOfPossibleMasters);
        int counter = 0;
        for (DiscoveryNode nextPossibleMaster : sortedNodes) {
            if (++counter >= numberOfPossibleMasters) {
                break;
            }
            nextPossibleMasters.add(nextPossibleMaster);
        }
        return nextPossibleMasters.toArray(new DiscoveryNode[nextPossibleMasters.size()]);
    }

    /**
     * Elects a new master out of the possible nodes, returning it. Returns null
     * if no master has been elected.
     */
    public DiscoveryNode electMaster(Iterable nodes) {
        List sortedNodes = sortedMasterNodes(nodes);
        if (sortedNodes == null || sortedNodes.isEmpty()) {
            return null;
        }
        DiscoveryNode masterNode = sortedNodes.get(0);
        // Sanity check: maybe we don't end up here, because serialization may have failed.
        if (masterNode.getVersion().before(minMasterVersion)) {
            logger.warn("ignoring master [{}], because the version [{}] is lower than the minimum compatible version [{}]", masterNode, masterNode.getVersion(), minMasterVersion);
            return null;
        } else {
            return masterNode;
        }
    }

    private List sortedMasterNodes(Iterable nodes) {
        List possibleNodes = CollectionUtils.iterableAsArrayList(nodes);
        if (possibleNodes.isEmpty()) {
            return null;
        }
        // clean non master nodes
        for (Iterator it = possibleNodes.iterator(); it.hasNext(); ) {
            DiscoveryNode node = it.next();
            if (!node.masterNode()) {
                it.remove();
            }
        }
        CollectionUtil.introSort(possibleNodes, nodeComparator);
        return possibleNodes;
    }

    private static class NodeComparator implements Comparator {

        @Override
        public int compare(DiscoveryNode o1, DiscoveryNode o2) {
            if (o1.masterNode() && !o2.masterNode()) {
                return -1;
            }
            if (!o1.masterNode() && o2.masterNode()) {
                return 1;
            }
            return o1.id().compareTo(o2.id());
        }
    }
}