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/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * 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.
 */

/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.cluster.routing.allocation.command;

import org.opensearch.cluster.node.DiscoveryNode;
import org.opensearch.cluster.routing.RoutingNode;
import org.opensearch.cluster.routing.RoutingNodes;
import org.opensearch.cluster.routing.ShardRouting;
import org.opensearch.cluster.routing.allocation.RerouteExplanation;
import org.opensearch.cluster.routing.allocation.RoutingAllocation;
import org.opensearch.cluster.routing.allocation.decider.Decision;
import org.opensearch.core.ParseField;
import org.opensearch.core.common.io.stream.StreamInput;
import org.opensearch.core.xcontent.ObjectParser;
import org.opensearch.core.xcontent.XContentParser;
import org.opensearch.index.IndexNotFoundException;
import org.opensearch.index.shard.ShardNotFoundException;

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

/**
 * Allocates an unassigned replica shard to a specific node. Checks if allocation deciders allow allocation.
 *
 * @opensearch.internal
 */
public class AllocateReplicaAllocationCommand extends AbstractAllocateAllocationCommand {
    public static final String NAME = "allocate_replica";
    public static final ParseField COMMAND_NAME_FIELD = new ParseField(NAME);

    private static final ObjectParser REPLICA_PARSER = createAllocateParser(NAME);

    /**
     * Creates a new {@link AllocateReplicaAllocationCommand}
     *
     * @param index          index of the shard to assign
     * @param shardId        id of the shard to assign
     * @param node           node id of the node to assign the shard to
     */
    public AllocateReplicaAllocationCommand(String index, int shardId, String node) {
        super(index, shardId, node);
    }

    /**
     * Read from a stream.
     */
    public AllocateReplicaAllocationCommand(StreamInput in) throws IOException {
        super(in);
    }

    @Override
    public String name() {
        return NAME;
    }

    public static AllocateReplicaAllocationCommand fromXContent(XContentParser parser) throws IOException {
        return new Builder().parse(parser).build();
    }

    /**
     * A builder for the command.
     *
     * @opensearch.internal
     */
    protected static class Builder extends AbstractAllocateAllocationCommand.Builder {

        @Override
        public Builder parse(XContentParser parser) throws IOException {
            return REPLICA_PARSER.parse(parser, this, null);
        }

        @Override
        public AllocateReplicaAllocationCommand build() {
            validate();
            return new AllocateReplicaAllocationCommand(index, shard, node);
        }
    }

    @Override
    public RerouteExplanation execute(RoutingAllocation allocation, boolean explain) {
        final DiscoveryNode discoNode;
        try {
            discoNode = allocation.nodes().resolveNode(node);
        } catch (IllegalArgumentException e) {
            return explainOrThrowRejectedCommand(explain, allocation, e);
        }
        final RoutingNodes routingNodes = allocation.routingNodes();
        RoutingNode routingNode = routingNodes.node(discoNode.getId());
        if (routingNode == null) {
            return explainOrThrowMissingRoutingNode(allocation, explain, discoNode);
        }

        try {
            allocation.routingTable().shardRoutingTable(index, shardId).primaryShard();
        } catch (IndexNotFoundException | ShardNotFoundException e) {
            return explainOrThrowRejectedCommand(explain, allocation, e);
        }

        ShardRouting primaryShardRouting = null;
        for (RoutingNode node : allocation.routingNodes()) {
            for (ShardRouting shard : node) {
                if (shard.getIndexName().equals(index) && shard.getId() == shardId && shard.primary()) {
                    primaryShardRouting = shard;
                    break;
                }
            }
        }
        if (primaryShardRouting == null) {
            return explainOrThrowRejectedCommand(
                explain,
                allocation,
                "trying to allocate a replica shard [" + index + "][" + shardId + "], while corresponding primary shard is still unassigned"
            );
        }

        List replicaShardRoutings = new ArrayList<>();
        for (ShardRouting shard : allocation.routingNodes().unassigned()) {
            if (shard.getIndexName().equals(index) && shard.getId() == shardId && shard.primary() == false) {
                replicaShardRoutings.add(shard);
            }
        }

        ShardRouting shardRouting;
        if (replicaShardRoutings.isEmpty()) {
            return explainOrThrowRejectedCommand(
                explain,
                allocation,
                "all copies of [" + index + "][" + shardId + "] are already assigned. Use the move allocation command instead"
            );
        } else {
            shardRouting = replicaShardRoutings.get(0);
        }

        Decision decision = allocation.deciders().canAllocate(shardRouting, routingNode, allocation);
        if (decision.type() == Decision.Type.NO) {
            // don't use explainOrThrowRejectedCommand to keep the original "NO" decision
            if (explain) {
                return new RerouteExplanation(this, decision);
            }
            throw new IllegalArgumentException(
                "["
                    + name()
                    + "] allocation of ["
                    + index
                    + "]["
                    + shardId
                    + "] on node "
                    + discoNode
                    + " is not allowed, reason: "
                    + decision
            );
        }

        initializeUnassignedShard(allocation, routingNodes, routingNode, shardRouting);
        return new RerouteExplanation(this, decision);
    }
}