/*
    * 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;
  
  import javax.annotation.Nullable;
  
  /**
   * This class provides a skeletal implementation of the {@link SortedMultiset} interface.
   *
   * <p>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(emulated = true)
  abstract class AbstractSortedMultiset<E> extends AbstractMultiset<E> implements SortedMultiset<E> {
    @GwtTransient final Comparator<? super E> comparator;
  
    // needed for serialization
    @SuppressWarnings("unchecked")
    AbstractSortedMultiset() {
      this((Comparator) Ordering.natural());
    }
  
    AbstractSortedMultiset(Comparator<? super E> comparator) {
      this.comparator = checkNotNull(comparator);
    }
  
    @Override
    public SortedSet<E> elementSet() {
      return (SortedSet<E>) super.elementSet();
    }
  
    @Override
    SortedSet<E> createElementSet() {
      return new SortedMultisets.ElementSet<E>(this);
    }
  
    @Override
    public Comparator<? super E> comparator() {
      return comparator;
    }
  
    @Override
    public Entry<E> firstEntry() {
      Iterator<Entry<E>> entryIterator = entryIterator();
      return entryIterator.hasNext() ? entryIterator.next() : null;
    }
  
    @Override
    public Entry<E> lastEntry() {
      Iterator<Entry<E>> entryIterator = descendingEntryIterator();
      return entryIterator.hasNext() ? entryIterator.next() : null;
    }
  
    @Override
    public Entry<E> pollFirstEntry() {
      Iterator<Entry<E>> entryIterator = entryIterator();
      if (entryIterator.hasNext()) {
        Entry<E> result = entryIterator.next();
        result = Multisets.immutableEntry(result.getElement(), result.getCount());
        entryIterator.remove();
        return result;
      }
      return null;
    }
  
    @Override
    public Entry<E> pollLastEntry() {
      Iterator<Entry<E>> entryIterator = descendingEntryIterator();
      if (entryIterator.hasNext()) {
        Entry<E> result = entryIterator.next();
        result = Multisets.immutableEntry(result.getElement(), result.getCount());
        entryIterator.remove();
        return result;
      }
      return null;
    }
 
   @Override
   public SortedMultiset<E> subMultiset(@Nullable E fromElement, BoundType fromBoundType,
       @Nullable E toElement, BoundType toBoundType) {
     // These are checked elsewhere, but NullPointerTester wants them checked eagerly.
     checkNotNull(fromBoundType);
     checkNotNull(toBoundType);
     return tailMultiset(fromElement, fromBoundType).headMultiset(toElement, toBoundType);
   }
 
   abstract Iterator<Entry<E>> descendingEntryIterator();
 
   Iterator<E> descendingIterator() {
     return Multisets.iteratorImpl(descendingMultiset());
   }
 
   private transient SortedMultiset<E> descendingMultiset;
 
   @Override
   public SortedMultiset<E> descendingMultiset() {
     SortedMultiset<E> result = descendingMultiset;
     return (result == null) ? descendingMultiset = createDescendingMultiset() : result;
   }
 
   SortedMultiset<E> createDescendingMultiset() {
     return new DescendingMultiset<E>() {
       @Override
       SortedMultiset<E> forwardMultiset() {
         return AbstractSortedMultiset.this;
       }
 
       @Override
       Iterator<Entry<E>> entryIterator() {
         return descendingEntryIterator();
       }
 
       @Override
       public Iterator<E> iterator() {
         return descendingIterator();
       }
     };
   }
 }