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.memory;
  
  import java.util.PriorityQueue;
  import java.util.SortedSet;
  import javax.annotation.concurrent.NotThreadSafe;
  
  import org.apache.cassandra.index.sai.iterators.KeyRangeIterator;
  import org.apache.cassandra.index.sai.utils.PrimaryKey;
  
  @NotThreadSafe
  public class InMemoryKeyRangeIterator extends KeyRangeIterator
  {
      private final PriorityQueue<PrimaryKey> keys;
      private final boolean uniqueKeys;
      private PrimaryKey lastKey;
  
      /**
       * An in-memory {@link KeyRangeIterator} that uses a {@link PriorityQueue} built from a {@link SortedSet}
       * which has no duplication as its backing store.
       */
      public InMemoryKeyRangeIterator(SortedSet<PrimaryKey> keys)
      {
          super(keys.first(), keys.last(), keys.size(), () -> {});
          this.keys = new PriorityQueue<>(keys);
          this.uniqueKeys = true;
      }
  
      /**
       * An in-memory {@link KeyRangeIterator} that uses a {@link PriorityQueue} which may
       * contain duplicated keys as its backing store.
       */
      public InMemoryKeyRangeIterator(PrimaryKey min, PrimaryKey max, PriorityQueue<PrimaryKey> keys)
      {
          super(min, max, keys.size(), () -> {});
          this.keys = keys;
          this.uniqueKeys = false;
      }
  
      @Override
      protected PrimaryKey computeNext()
      {
          PrimaryKey key = computeNextKey();
          return key == null ? endOfData() : key;
      }
  
      protected PrimaryKey computeNextKey()
      {
          PrimaryKey next = null;
  
          while (!keys.isEmpty())
          {
              PrimaryKey key = keys.poll();
              if (uniqueKeys)
                  return key;
  
              if (lastKey == null || lastKey.compareTo(key, false) != 0)
              {
                  next = key;
                  lastKey = key;
                  break;
              }
          }
  
          return next;
      }
  
      @Override
      protected void performSkipTo(PrimaryKey nextKey)
      {
          while (!keys.isEmpty())
          {
              PrimaryKey key = keys.peek();
              if (key.compareTo(nextKey, false) >= 0)
                  break;
  
              // consume smaller key
              keys.poll();
          }
      }
  
      @Override
      public void close()
      {}
  }
  