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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.apache.kafka.clients.consumer;

import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import org.apache.kafka.clients.consumer.internals.AbstractStickyAssignor;
import org.apache.kafka.common.TopicPartition;

/**
 * A cooperative version of the {@link AbstractStickyAssignor AbstractStickyAssignor}. This follows the same (sticky)
 * assignment logic as {@link StickyAssignor StickyAssignor} but allows for cooperative rebalancing while the
 * {@link StickyAssignor StickyAssignor} follows the eager rebalancing protocol. See
 * {@link ConsumerPartitionAssignor.RebalanceProtocol} for an explanation of the rebalancing protocols.
 * 
 * Users should prefer this assignor for newer clusters.
 * 

 * To turn on cooperative rebalancing you must set all your consumers to use this {@code PartitionAssignor},
 * or implement a custom one that returns {@code RebalanceProtocol.COOPERATIVE} in
 * {@link CooperativeStickyAssignor#supportedProtocols supportedProtocols()}.
 * 
 * IMPORTANT: if upgrading from 2.3 or earlier, you must follow a specific upgrade path in order to safely turn on
 * cooperative rebalancing. See the upgrade guide for details.
 */
public class CooperativeStickyAssignor extends AbstractStickyAssignor {

    @Override
    public String name() {
        return "cooperative-sticky";
    }

    @Override
    public List supportedProtocols() {
        return Arrays.asList(RebalanceProtocol.COOPERATIVE, RebalanceProtocol.EAGER);
    }

    @Override
    protected MemberData memberData(Subscription subscription) {
        return new MemberData(subscription.ownedPartitions(), Optional.empty());
    }

    @Override
    public Map> assign(Map partitionsPerTopic,
                                                    Map subscriptions) {
        Map> assignments = super.assign(partitionsPerTopic, subscriptions);

        Map partitionsTransferringOwnership = super.partitionsTransferringOwnership == null ?
            computePartitionsTransferringOwnership(subscriptions, assignments) :
            super.partitionsTransferringOwnership;

        adjustAssignment(assignments, partitionsTransferringOwnership);
        return assignments;
    }

    // Following the cooperative rebalancing protocol requires removing partitions that must first be revoked from the assignment
    private void adjustAssignment(Map> assignments,
                                  Map partitionsTransferringOwnership) {
        for (Map.Entry partitionEntry : partitionsTransferringOwnership.entrySet()) {
            assignments.get(partitionEntry.getValue()).remove(partitionEntry.getKey());
        }
    }

    private Map computePartitionsTransferringOwnership(Map subscriptions,
                                                                               Map> assignments) {
        Map allAddedPartitions = new HashMap<>();
        Set allRevokedPartitions = new HashSet<>();

        for (final Map.Entry> entry : assignments.entrySet()) {
            String consumer = entry.getKey();

            List ownedPartitions = subscriptions.get(consumer).ownedPartitions();
            List assignedPartitions = entry.getValue();

            Set ownedPartitionsSet = new HashSet<>(ownedPartitions);
            for (TopicPartition tp : assignedPartitions) {
                if (!ownedPartitionsSet.contains(tp))
                    allAddedPartitions.put(tp, consumer);
            }

            Set assignedPartitionsSet = new HashSet<>(assignedPartitions);
            for (TopicPartition tp : ownedPartitions) {
                if (!assignedPartitionsSet.contains(tp))
                    allRevokedPartitions.add(tp);
            }
        }

        allAddedPartitions.keySet().retainAll(allRevokedPartitions);
        return allAddedPartitions;
    }
}