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   * 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.
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  package org.apache.cassandra.index.internal.keys;
  
  import java.nio.ByteBuffer;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.db.Clustering;
  import org.apache.cassandra.db.DecoratedKey;
  import org.apache.cassandra.db.DeletionTime;
  import org.apache.cassandra.db.ReadCommand;
  import org.apache.cassandra.db.ReadExecutionController;
  import org.apache.cassandra.db.SinglePartitionReadCommand;
  import org.apache.cassandra.db.WriteContext;
  import org.apache.cassandra.db.filter.ColumnFilter;
  import org.apache.cassandra.db.filter.DataLimits;
  import org.apache.cassandra.db.filter.RowFilter;
  import org.apache.cassandra.db.partitions.UnfilteredPartitionIterator;
  import org.apache.cassandra.db.rows.Row;
  import org.apache.cassandra.db.rows.RowIterator;
  import org.apache.cassandra.db.rows.Rows;
  import org.apache.cassandra.db.rows.UnfilteredRowIterator;
  import org.apache.cassandra.index.Index;
  import org.apache.cassandra.index.internal.CassandraIndex;
  import org.apache.cassandra.index.internal.CassandraIndexSearcher;
  import org.apache.cassandra.schema.TableMetadata;
  
  public class KeysSearcher extends CassandraIndexSearcher
  {
      private static final Logger logger = LoggerFactory.getLogger(KeysSearcher.class);
  
      public KeysSearcher(ReadCommand command,
                          RowFilter.Expression expression,
                          CassandraIndex indexer)
      {
          super(command, expression, indexer);
      }
  
      protected UnfilteredPartitionIterator queryDataFromIndex(final DecoratedKey indexKey,
                                                               final RowIterator indexHits,
                                                               final ReadCommand command,
                                                               final ReadExecutionController executionController)
      {
          assert indexHits.staticRow() == Rows.EMPTY_STATIC_ROW;
  
          return new UnfilteredPartitionIterator()
          {
              private UnfilteredRowIterator next;
  
              public TableMetadata metadata()
              {
                  return command.metadata();
              }
  
              public boolean hasNext()
              {
                  return prepareNext();
              }
  
              public UnfilteredRowIterator next()
              {
                  if (next == null)
                      prepareNext();
  
                  UnfilteredRowIterator toReturn = next;
                  next = null;
                  return toReturn;
              }
  
              private boolean prepareNext()
              {
                  while (next == null && indexHits.hasNext())
                  {
                      Row hit = indexHits.next();
                      DecoratedKey key = index.baseCfs.decorateKey(hit.clustering().bufferAt(0));
                      if (!command.selectsKey(key))
                          continue;
  
                      ColumnFilter extendedFilter = getExtendedFilter(command.columnFilter());
                      SinglePartitionReadCommand dataCmd = SinglePartitionReadCommand.create(index.baseCfs.metadata(),
                                                                                             command.nowInSec(),
                                                                                             extendedFilter,
                                                                                             command.rowFilter(),
                                                                                             DataLimits.NONE,
                                                                                             key,
                                                                                             command.clusteringIndexFilter(key),
                                                                                             (Index.QueryPlan) null);
  
                                                    // Otherwise, we close right away if empty, and if it's assigned to next it will be called either
                                                    // by the next caller of next, or through closing this iterator is this come before.
                      UnfilteredRowIterator dataIter = filterIfStale(dataCmd.queryMemtableAndDisk(index.baseCfs, executionController),
                                                                     hit,
                                                                     indexKey.getKey(),
                                                                     executionController.getWriteContext(),
                                                                     command.nowInSec());
  
                      if (dataIter != null)
                      {
                          if (dataIter.isEmpty())
                              dataIter.close();
                          else
                              next = dataIter;
                      }
                  }
                  return next != null;
              }
  
              public void remove()
              {
                  throw new UnsupportedOperationException();
              }
  
              public void close()
              {
                  indexHits.close();
                  if (next != null)
                      next.close();
              }
          };
      }
  
      private ColumnFilter getExtendedFilter(ColumnFilter initialFilter)
      {
          if (command.columnFilter().fetches(index.getIndexedColumn()))
              return initialFilter;
  
          ColumnFilter.Builder builder = ColumnFilter.selectionBuilder();
          builder.addAll(initialFilter.fetchedColumns());
          builder.add(index.getIndexedColumn());
          return builder.build();
      }
  
      private UnfilteredRowIterator filterIfStale(UnfilteredRowIterator iterator,
                                                  Row indexHit,
                                                  ByteBuffer indexedValue,
                                                  WriteContext ctx,
                                                  long nowInSec)
      {
          Row data = iterator.staticRow();
          if (index.isStale(data, indexedValue, nowInSec))
          {
              // Index is stale, remove the index entry and ignore
              index.deleteStaleEntry(index.getIndexCfs().decorateKey(indexedValue),
                                     makeIndexClustering(iterator.partitionKey().getKey(), Clustering.EMPTY),
                                     DeletionTime.build(indexHit.primaryKeyLivenessInfo().timestamp(), nowInSec),
                                     ctx);
              iterator.close();
              return null;
          }
          else
          {
              return iterator;
          }
      }
  }
  