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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.
   *
   */
  package org.apache.cassandra.utils;
  
  import java.util.*;
  
  /**
   * A class for iterating sequentially through an ordered collection and efficiently
   * finding the overlapping set of matching intervals.
   *
   * The algorithm is quite simple: the intervals are sorted ascending by both min and max
   * in two separate lists. These lists are walked forwards each time we visit a new point,
   * with the set of intervals in the min-ordered list being added to our set of overlaps,
   * and those in the max-ordered list being removed.
   */
  public class OverlapIterator<I extends Comparable<? super I>, V>
  {
      // indexing into sortedByMin, tracks the next interval to include
      int nextToInclude;
      final List<Interval<I, V>> sortedByMin;
      // indexing into sortedByMax, tracks the next interval to exclude
      int nextToExclude;
      final List<Interval<I, V>> sortedByMax;
      final Set<V> overlaps = new HashSet<>();
      final Set<V> accessible = Collections.unmodifiableSet(overlaps);
  
      public OverlapIterator(Collection<Interval<I, V>> intervals)
      {
          sortedByMax = new ArrayList<>(intervals);
          Collections.sort(sortedByMax, Interval.<I, V>maxOrdering());
          // we clone after first sorting by max;  this is quite likely to make sort cheaper, since a.max < b.max
          // generally increases the likelihood that a.min < b.min, so the list may be partially sorted already.
          // this also means if (in future) we sort either collection (or a subset thereof) by the other's comparator
          // all items, including equal, will occur in the same order, including
          sortedByMin = new ArrayList<>(sortedByMax);
          Collections.sort(sortedByMin, Interval.<I, V>minOrdering());
      }
  
      // move the iterator forwards to the overlaps matching point
      public void update(I point)
      {
          // we don't use binary search here since we expect points to be a superset of the min/max values
  
          // add those we are now after the start of
          while (nextToInclude < sortedByMin.size() && sortedByMin.get(nextToInclude).min.compareTo(point) <= 0)
              overlaps.add(sortedByMin.get(nextToInclude++).data);
          // remove those we are now after the end of
          while (nextToExclude < sortedByMax.size() && sortedByMax.get(nextToExclude).max.compareTo(point) < 0)
              overlaps.remove(sortedByMax.get(nextToExclude++).data);
      }
  
      public Set<V> overlaps()
      {
          return accessible;
      }
  }
  