content: /*
   * 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.streams.processor.internals;
  
  import org.apache.kafka.common.Cluster;
  import org.apache.kafka.common.PartitionInfo;
  import org.apache.kafka.common.TopicPartition;
  import org.apache.kafka.streams.errors.StreamsException;
  import org.apache.kafka.streams.processor.TaskId;
  import org.apache.kafka.streams.processor.internals.TopologyMetadata.Subtopology;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * Groups partitions by the partition id.
   *
   * Join operations requires that topics of the joining entities are copartitioned, i.e., being partitioned by the same key and having the same
   * number of partitions. Copartitioning is ensured by having the same number of partitions on
   * joined topics, and by using the serialization and Producer's default partitioner.
   */
  public class PartitionGrouper {
  
      private static final Logger log = LoggerFactory.getLogger(PartitionGrouper.class);
  
      /**
       * Generate tasks with the assigned topic partitions.
       *
       * @param topicGroups   group of topics that need to be joined together
       * @param metadata      metadata of the consuming cluster
       * @return The map from generated task ids to the assigned partitions
       */
      public Map<TaskId, Set<TopicPartition>> partitionGroups(final Map<Subtopology, Set<String>> topicGroups, final Cluster metadata) {
          return partitionGroups(topicGroups, new HashMap<>(), new HashMap<>(), metadata);
      }
  
      /**
       * Generate tasks with the assigned topic partitions.
       *
       * @param sourceTopicGroups        group of source topics that need to be joined together
       * @param changelogTopicGroups     group of changelog topics that need to be joined together
       * @param changelogPartitionGroups the output grouping of the changelog topic partitions by task
       *                                 id. This input will be mutated.
       * @param metadata                 metadata of the consuming cluster
       * @return The map from generated task ids to the assigned partitions
       */
      public Map<TaskId, Set<TopicPartition>> partitionGroups(final Map<Subtopology, Set<String>> sourceTopicGroups,
                                                              final Map<Subtopology, Set<String>> changelogTopicGroups,
                                                              final Map<TaskId, Set<TopicPartition>> changelogPartitionGroups,
                                                              final Cluster metadata) {
          final Map<TaskId, Set<TopicPartition>> sourcePartitionGroups = new HashMap<>();
  
          for (final Map.Entry<Subtopology, Set<String>> entry : sourceTopicGroups.entrySet()) {
              final Subtopology subtopology = entry.getKey();
              final Set<String> sourceTopicGroup = entry.getValue();
              final Set<String> changelogTopicGroup = changelogTopicGroups.getOrDefault(subtopology, new HashSet<>());
  
              final int maxNumPartitions = maxNumPartitions(metadata, sourceTopicGroup);
  
              for (int partitionId = 0; partitionId < maxNumPartitions; partitionId++) {
                  final Set<TopicPartition> sourcePartitionGroup = new HashSet<>(sourceTopicGroup.size());
                  final Set<TopicPartition> changelogPartitionGroup = new HashSet<>(changelogTopicGroup.size());
  
                  for (final String topic : sourceTopicGroup) {
                      final List<PartitionInfo> partitions = metadata.partitionsForTopic(topic);
                      if (partitionId < partitions.size()) {
                          sourcePartitionGroup.add(new TopicPartition(topic, partitionId));
                      }
                  }
  
                  for (final String topic : changelogTopicGroup) {
                      changelogPartitionGroup.add(new TopicPartition(topic, partitionId));
                  }
  
                  final TaskId taskId = new TaskId(subtopology.nodeGroupId, partitionId, subtopology.namedTopology);
                  sourcePartitionGroups.put(taskId, Collections.unmodifiableSet(sourcePartitionGroup));
                  changelogPartitionGroups.put(taskId, Collections.unmodifiableSet(changelogPartitionGroup));
              }
          }
  
          return Collections.unmodifiableMap(sourcePartitionGroups);
      }
  
      /**
       * @throws StreamsException if no metadata can be received for a topic
       */
      protected int maxNumPartitions(final Cluster metadata, final Set<String> topics) {
          int maxNumPartitions = 0;
          for (final String topic : topics) {
              final List<PartitionInfo> partitions = metadata.partitionsForTopic(topic);
              if (partitions.isEmpty()) {
                  log.error("Empty partitions for topic {}", topic);
                  throw new RuntimeException("Empty partitions for topic " + topic);
              }
  
              final int numPartitions = partitions.size();
              if (numPartitions > maxNumPartitions) {
                  maxNumPartitions = numPartitions;
              }
          }
          return maxNumPartitions;
      }
  
  }
  