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.storage.internals.checkpoint;
  
  import org.apache.kafka.common.TopicPartition;
  
  import java.util.Map;
  import java.util.Optional;
  import java.util.stream.Collectors;
  
  /**
   * Loads checkpoint files on demand and caches the offsets for reuse.
   */
  public class LazyOffsetCheckpoints implements OffsetCheckpoints {
  
      private final Map<String, LazyOffsetCheckpointMap> lazyCheckpointsByLogDir;
  
      public LazyOffsetCheckpoints(Map<String, OffsetCheckpointFile> checkpointsByLogDir) {
          lazyCheckpointsByLogDir = checkpointsByLogDir.entrySet().stream()
                  .collect(Collectors.toMap(Map.Entry::getKey, entry -> new LazyOffsetCheckpointMap(entry.getValue())));
      }
  
      @Override
      public Optional<Long> fetch(String logDir, TopicPartition topicPartition) {
          LazyOffsetCheckpointMap offsetCheckpointFile = lazyCheckpointsByLogDir.get(logDir);
          if (offsetCheckpointFile == null) {
              throw new IllegalArgumentException("No checkpoint file for log dir " + logDir);
          }
          return offsetCheckpointFile.fetch(topicPartition);
      }
  
      static class LazyOffsetCheckpointMap {
          private Map<TopicPartition, Long> offsets;
          private final OffsetCheckpointFile checkpoint;
  
          LazyOffsetCheckpointMap(OffsetCheckpointFile checkpoint) {
              this.checkpoint = checkpoint;
          }
  
          synchronized Optional<Long> fetch(TopicPartition topicPartition) {
              if (offsets == null) {
                  offsets = checkpoint.read();
              }
              return Optional.ofNullable(offsets.get(topicPartition));
          }
      }
  }
  