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/*
 * Copyright (C) 2011 The Guava Authors
 * 
 * Licensed 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 com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;

import java.util.Comparator;
import java.util.Iterator;
import java.util.SortedSet;

/**
 * This class provides a skeletal implementation of the {@link SortedMultiset} interface.
 *
 * The {@link #count} and {@link #size} implementations all iterate across the set returned by
 * {@link Multiset#entrySet()}, as do many methods acting on the set returned by
 * {@link #elementSet()}. Override those methods for better performance.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
abstract class AbstractSortedMultiset extends AbstractMultiset implements SortedMultiset {
  final Comparator comparator;

  // needed for serialization
  @SuppressWarnings("unchecked")
  AbstractSortedMultiset() {
    this((Comparator) Ordering.natural());
  }
  
  AbstractSortedMultiset(Comparator comparator) {
    this.comparator = checkNotNull(comparator);
  }

  @Override
  public SortedSet elementSet() {
    return (SortedSet) super.elementSet();
  }

  @Override
  SortedSet createElementSet() {
    return new SortedMultisets.ElementSet() {
      @Override
      SortedMultiset multiset() {
        return AbstractSortedMultiset.this;
      }
    };
  }

  @Override
  public Comparator comparator() {
    return comparator;
  }

  @Override
  public Entry firstEntry() {
    Iterator> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public Entry lastEntry() {
    Iterator> entryIterator = descendingEntryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public Entry pollFirstEntry() {
    Iterator> entryIterator = entryIterator();
    if (entryIterator.hasNext()) {
      Entry result = entryIterator.next();
      result = Multisets.immutableEntry(result.getElement(), result.getCount());
      entryIterator.remove();
      return result;
    }
    return null;
  }

  @Override
  public Entry pollLastEntry() {
    Iterator> entryIterator = descendingEntryIterator();
    if (entryIterator.hasNext()) {
      Entry result = entryIterator.next();
      result = Multisets.immutableEntry(result.getElement(), result.getCount());
      entryIterator.remove();
      return result;
    }
    return null;
  }

  @Override
  public SortedMultiset subMultiset(E fromElement, BoundType fromBoundType, E toElement,
      BoundType toBoundType) {
    return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
  }

  abstract Iterator> descendingEntryIterator();

  Iterator descendingIterator() {
    return Multisets.iteratorImpl(descendingMultiset());
  }

  private transient SortedMultiset descendingMultiset;

  @Override
  public SortedMultiset descendingMultiset() {
    SortedMultiset result = descendingMultiset;
    return (result == null) ? descendingMultiset = createDescendingMultiset() : result;
  }

  SortedMultiset createDescendingMultiset() {
    return new SortedMultisets.DescendingMultiset() {
      @Override
      SortedMultiset forwardMultiset() {
        return AbstractSortedMultiset.this;
      }

      @Override
      Iterator> entryIterator() {
        return descendingEntryIterator();
      }

      @Override
      public Iterator iterator() {
        return descendingIterator();
      }
    };
  }
}