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.bifromq.basekv.store.range;
  
  import static org.apache.bifromq.basekv.utils.BoundaryUtil.inRange;
  
  import org.apache.bifromq.basekv.localengine.IKVSpaceIterator;
  import org.apache.bifromq.basekv.localengine.IKVSpaceReader;
  import org.apache.bifromq.basekv.proto.Boundary;
  import org.apache.bifromq.basekv.store.api.IKVCloseableReader;
  import org.apache.bifromq.basekv.store.api.IKVIterator;
  import org.apache.bifromq.basekv.store.api.IKVRangeReader;
  import com.google.protobuf.ByteString;
  import java.util.Optional;
  
  public class KVReader implements IKVCloseableReader {
      private final IKVSpaceReader kvSpace;
      private final IKVRangeReader kvRangeReader;
      private volatile IKVSpaceIterator kvSpaceIterator;
  
      KVReader(IKVSpaceReader kvSpace, IKVRangeReader reader) {
          this.kvSpace = kvSpace;
          this.kvRangeReader = reader;
      }
  
      @Override
      public Boundary boundary() {
          return kvRangeReader.boundary();
      }
  
      @Override
      public long size(Boundary boundary) {
          assert inRange(boundary, boundary());
          return kvRangeReader.size(boundary);
      }
  
      @Override
      public boolean exist(ByteString key) {
          assert inRange(key, boundary());
          return kvSpace.exist(key);
      }
  
      @Override
      public Optional<ByteString> get(ByteString key) {
          assert inRange(key, boundary());
          return kvSpace.get(key);
      }
  
      @Override
      public IKVIterator iterator() {
          return new KVIterator(getKvSpaceIterator());
      }
  
      @Override
      public void refresh() {
          getKvSpaceIterator().refresh();
      }
  
      private IKVSpaceIterator getKvSpaceIterator() {
          if (kvSpaceIterator == null) {
              synchronized (this) {
                  if (kvSpaceIterator == null) {
                      this.kvSpaceIterator = kvSpace.newIterator();
                  }
              }
          }
          return kvSpaceIterator;
      }
  
      @Override
      public void close() {
          if (kvSpaceIterator != null) {
              kvSpaceIterator.close();
          }
      }
  }
  