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;
  
  import org.apache.kafka.common.TopicPartition;
  
  public interface StandbyUpdateListener {
  
      enum SuspendReason {
          MIGRATED,
          PROMOTED
      }
  
      /**
       * A callback that will be invoked after registering the changelogs for each state store in a standby
       * task. It is guaranteed to always be invoked before any records are loaded into the standby store.
       *
       * @param topicPartition the changelog TopicPartition for this standby task
       * @param storeName the name of the store being loaded
       * @param startingOffset the offset from which the standby task begins consuming from the changelog
       */
      void onUpdateStart(final TopicPartition topicPartition,
                         final String storeName,
                         final long startingOffset);
  
      /**
       * Method called after loading a batch of records. In this case the maximum size of the batch is whatever
       * the value of the MAX_POLL_RECORDS is set to.
       * <n>
       * This method is called after loading each batch and it is advised to keep processing to a minimum.
       * Any heavy processing will block the state updater thread and slow down the rate of standby task 
       * loading. Therefore, if you need to do any extended processing or connect to an external service,
       * consider doing so asynchronously.
       *
       * @param topicPartition the changelog TopicPartition for this standby task
       * @param storeName the name of the store being loaded
       * @param batchEndOffset batchEndOffset the changelog end offset (inclusive) of the batch that was just loaded
       * @param batchSize the total number of records in the batch that was just loaded
       * @param currentEndOffset the current end offset of the changelog topic partition.
       */
      void onBatchLoaded(final TopicPartition topicPartition,
                         final String storeName,
                         final TaskId taskId,
                         final long batchEndOffset,
                         final long batchSize,
                         final long currentEndOffset);
  
      /**
       * This method is called when the corresponding standby task stops updating, for the provided reason.
       * <p>
       * If the task was {@code MIGRATED} to another instance, this callback will be invoked after this
       * state store (and the task itself) are closed (in which case the data will be cleaned up after 
       * state.cleanup.delay.ms).
       * If the task was {@code PROMOTED} to an active task, the state store will not be closed, and the 
       * callback will be invoked after unregistering it as a standby task but before re-registering it as an active task 
       * and beginning restoration. In other words, this will always called before the corresponding 
       * {@link StateRestoreListener#onRestoreStart} call is made.
       *
       * @param topicPartition the changelog TopicPartition for this standby task
       * @param storeName the name of the store being loaded
       * @param storeOffset is the offset of the last changelog record that was read and put into the store at the time
       * of suspension.
       * @param currentEndOffset the current end offset of the changelog topic partition.
       * @param reason is the reason why the standby task was suspended.
       */
      void onUpdateSuspended(final TopicPartition topicPartition,
                             final String storeName,
                             final long storeOffset,
                             final long currentEndOffset,
                             final SuspendReason reason);
  }