/*
 * 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.cluster.routing.allocation;

import com.google.common.collect.Maps;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.io.stream.Streamable;
import org.elasticsearch.index.shard.ShardId;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * Instances of this class keeps explanations of decisions that have been made by allocation.
 * An {@link AllocationExplanation} consists of a set of per node explanations.
 * Since {@link NodeExplanation}s are related to shards an {@link AllocationExplanation} maps
 * a shards id to a set of {@link NodeExplanation}s.  
 */
public class AllocationExplanation implements Streamable {

    public static final AllocationExplanation EMPTY = new AllocationExplanation();

    /**
     * Instances of this class keep messages and informations about nodes of an allocation
     */
    public static class NodeExplanation {
        private final DiscoveryNode node;

        private final String description;

        /**
         * Creates a new {@link NodeExplanation}
         *  
         * @param node node referenced by this {@link NodeExplanation}
         * @param description a message associated with the given node 
         */
        public NodeExplanation(DiscoveryNode node, String description) {
            this.node = node;
            this.description = description;
        }

        /**
         * The node referenced by the explanation
         * @return referenced node
         */
        public DiscoveryNode node() {
            return node;
        }

        /**
         * Get the explanation for the node
         * @return explanation for the node
         */
        public String description() {
            return description;
        }
    }

    private final Map<ShardId, List<NodeExplanation>> explanations = Maps.newHashMap();

    /**
     * Create and add a node explanation to this explanation referencing a shard  
     * @param shardId id the of the referenced shard
     * @param nodeExplanation Explanation itself
     * @return AllocationExplanation involving the explanation 
     */
    public AllocationExplanation add(ShardId shardId, NodeExplanation nodeExplanation) {
        List<NodeExplanation> list = explanations.get(shardId);
        if (list == null) {
            list = new ArrayList<>();
            explanations.put(shardId, list);
        }
        list.add(nodeExplanation);
        return this;
    }

    /**
     * List of explanations involved by this AllocationExplanation
     * @return Map of shard ids and corresponding explanations  
     */
    public Map<ShardId, List<NodeExplanation>> explanations() {
        return this.explanations;
    }

    /**
     * Read an {@link AllocationExplanation} from an {@link StreamInput}
     * @param in {@link StreamInput} to read from
     * @return a new {@link AllocationExplanation} read from the stream 
     * @throws IOException if something bad happened while reading
     */
    public static AllocationExplanation readAllocationExplanation(StreamInput in) throws IOException {
        AllocationExplanation e = new AllocationExplanation();
        e.readFrom(in);
        return e;
    }

    @Override
    public void readFrom(StreamInput in) throws IOException {
        int size = in.readVInt();
        for (int i = 0; i < size; i++) {
            ShardId shardId = ShardId.readShardId(in);
            int size2 = in.readVInt();
            List<NodeExplanation> ne = new ArrayList<>(size2);
            for (int j = 0; j < size2; j++) {
                DiscoveryNode node = null;
                if (in.readBoolean()) {
                    node = DiscoveryNode.readNode(in);
                }
                ne.add(new NodeExplanation(node, in.readString()));
            }
            explanations.put(shardId, ne);
        }
    }

    @Override
    public void writeTo(StreamOutput out) throws IOException {
        out.writeVInt(explanations.size());
        for (Map.Entry<ShardId, List<NodeExplanation>> entry : explanations.entrySet()) {
            entry.getKey().writeTo(out);
            out.writeVInt(entry.getValue().size());
            for (NodeExplanation nodeExplanation : entry.getValue()) {
                if (nodeExplanation.node() == null) {
                    out.writeBoolean(false);
                } else {
                    out.writeBoolean(true);
                    nodeExplanation.node().writeTo(out);
                }
                out.writeString(nodeExplanation.description());
            }
        }
    }
}