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   * Licensed to the Apache Software Foundation (ASF) under one
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   * distributed with this work for additional information
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   * 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
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   * See the License for the specific language governing permissions and
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  package org.apache.cassandra.service.reads.range;
  
  import java.util.Iterator;
  
  import com.google.common.collect.Iterators;
  import com.google.common.collect.PeekingIterator;
  
  import org.apache.cassandra.db.ConsistencyLevel;
  import org.apache.cassandra.db.Keyspace;
  import org.apache.cassandra.locator.ReplicaPlan;
  import org.apache.cassandra.locator.ReplicaPlans;
  import org.apache.cassandra.schema.TableId;
  import org.apache.cassandra.tcm.ClusterMetadata;
  import org.apache.cassandra.utils.AbstractIterator;
  
  class ReplicaPlanMerger extends AbstractIterator<ReplicaPlan.ForRangeRead>
  {
      private final Keyspace keyspace;
      private final ConsistencyLevel consistency;
      private final TableId tableId;
      private final PeekingIterator<ReplicaPlan.ForRangeRead> ranges;
  
      ReplicaPlanMerger(Iterator<ReplicaPlan.ForRangeRead> iterator, Keyspace keyspace, TableId tableId, ConsistencyLevel consistency)
      {
          this.keyspace = keyspace;
          this.tableId = tableId;
          this.consistency = consistency;
          this.ranges = Iterators.peekingIterator(iterator);
      }
  
      @Override
      protected ReplicaPlan.ForRangeRead computeNext()
      {
          if (!ranges.hasNext())
              return endOfData();
  
          ReplicaPlan.ForRangeRead current = ranges.next();
          ClusterMetadata metadata = ClusterMetadata.current();
  
          // getRestrictedRange has broken the queried range into per-[vnode] token ranges, but this doesn't take
          // the replication factor into account. If the intersection of live endpoints for 2 consecutive ranges
          // still meets the CL requirements, then we can merge both ranges into the same RangeSliceCommand.
          while (ranges.hasNext())
          {
              // If the current range right is the min token, we should stop merging because CFS.getRangeSlice
              // don't know how to deal with a wrapping range.
              // Note: it would be slightly more efficient to have CFS.getRangeSlice on the destination nodes unwraps
              // the range if necessary and deal with it. However, we can't start sending wrapped range without breaking
              // wire compatibility, so it's likely easier not to bother;
              if (current.range().right.isMinimum())
                  break;
  
              ReplicaPlan.ForRangeRead next = ranges.peek();
              ReplicaPlan.ForRangeRead merged = ReplicaPlans.maybeMerge(metadata, keyspace, tableId, consistency, current, next);
              if (merged == null)
                  break;
  
              current = merged;
              ranges.next(); // consume the range we just merged since we've only peeked so far
          }
          return current;
      }
  }
  