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.fqltool;
  
  import java.util.PriorityQueue;
  
  import net.openhft.chronicle.queue.ExcerptTailer;
  import org.apache.cassandra.utils.AbstractIterator;
  
  public class FQLQueryIterator extends AbstractIterator<FQLQuery>
  {
      // use a priority queue to be able to sort the head of the query logs in memory
      private final PriorityQueue<FQLQuery> pq;
      private final ExcerptTailer tailer;
      private final FQLQueryReader reader;
  
      /**
       * Create an iterator over the FQLQueries in tailer
       *
       * Reads up to readAhead queries in to memory to be able to sort them (the files are mostly sorted already)
       */
      public FQLQueryIterator(ExcerptTailer tailer, int readAhead)
      {
          assert readAhead > 0 : "readAhead needs to be > 0";
          reader = new FQLQueryReader();
          this.tailer = tailer;
          pq = new PriorityQueue<>(readAhead);
          for (int i = 0; i < readAhead; i++)
          {
              FQLQuery next = readNext();
              if (next != null)
                  pq.add(next);
              else
                  break;
          }
      }
  
      protected FQLQuery computeNext()
      {
          FQLQuery q = pq.poll();
          if (q == null)
              return endOfData();
          FQLQuery next = readNext();
          if (next != null)
              pq.add(next);
          return q;
      }
  
      private FQLQuery readNext()
      {
          if (tailer.readDocument(reader))
              return reader.getQuery();
          return null;
      }
  }
  
  