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.cassandra.index.sai.postings;
  
  import java.io.IOException;
  
  import javax.annotation.concurrent.NotThreadSafe;
  
  import org.apache.cassandra.utils.Throwables;
  
  /**
   * A peekable wrapper around a {@link PostingList} that allows the next value to be
   * looked at without advancing the state of the {@link PostingList}
   */
  @NotThreadSafe
  public class PeekablePostingList implements PostingList
  {
      private final PostingList wrapped;
  
      private boolean peeked = false;
      private long next;
  
      public static PeekablePostingList makePeekable(PostingList postingList)
      {
          return postingList instanceof PeekablePostingList ? (PeekablePostingList) postingList
                                                            : new PeekablePostingList(postingList);
      }
  
      private PeekablePostingList(PostingList wrapped)
      {
          this.wrapped = wrapped;
      }
  
      public long peek()
      {
          if (peeked)
              return next;
  
          try
          {
              peeked = true;
              return next = wrapped.nextPosting();
          }
          catch (IOException e)
          {
              throw Throwables.cleaned(e);
          }
      }
  
      public void advanceWithoutConsuming(long targetRowID) throws IOException
      {
          if (peek() == END_OF_STREAM)
              return;
  
          if (peek() >= targetRowID)
          {
              peek();
              return;
          }
  
          peeked = true;
          next = wrapped.advance(targetRowID);
      }
  
      @Override
      public long minimum()
      {
          return wrapped.maximum();
      }
  
      @Override
      public long maximum()
      {
          return wrapped.maximum();
      }
  
      @Override
      public long nextPosting() throws IOException
      {
          if (peeked)
          {
              peeked = false;
              return next;
          }
          return wrapped.nextPosting();
      }
  
      @Override
      public long size()
      {
          return wrapped.size();
      }
  
      @Override
      public long advance(long targetRowID) throws IOException
      {
          if (peeked && next >= targetRowID)
          {
              peeked = false;
              return next;
          }
  
          peeked = false;
          return wrapped.advance(targetRowID);
      }
  
      @Override
      public void close()
      {
          wrapped.close();
      }
  }
  