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.kstream.internals;
  
  import org.apache.kafka.clients.producer.internals.BuiltInPartitioner;
  import org.apache.kafka.streams.kstream.Windowed;
  import org.apache.kafka.streams.processor.StreamPartitioner;
  
  import java.util.Collections;
  import java.util.Optional;
  import java.util.Set;
  
  public class WindowedStreamPartitioner<K, V> implements StreamPartitioner<Windowed<K>, V> {
  
      private final WindowedSerializer<K> serializer;
  
      public WindowedStreamPartitioner(final WindowedSerializer<K> serializer) {
          this.serializer = serializer;
      }
  
      /**
       * WindowedStreamPartitioner determines the partition number for a record with the given windowed key and value
       * and the current number of partitions. The partition number id determined by the original key of the windowed key
       * using the same logic as DefaultPartitioner so that the topic is partitioned by the original key.
       *
       * @param topic the topic name this record is sent to
       * @param windowedKey the key of the record
       * @param value the value of the record
       * @param numPartitions the total number of partitions
       * @return an integer between 0 and {@code numPartitions-1}, or {@code null} if the default partitioning logic should be used
       */
      @Override
      public Optional<Set<Integer>> partitions(final String topic, final Windowed<K> windowedKey, final V value, final int numPartitions) {
          // for windowed key, the key bytes should never be null
          final byte[] keyBytes = serializer.serializeBaseKey(topic, windowedKey);
  
          // stick with the same built-in partitioner util functions that producer used
          // to make sure its behavior is consistent with the producer
          return Optional.of(Collections.singleton(BuiltInPartitioner.partitionForKey(keyBytes, numPartitions)));
      }
  }
  