/*
    * Copyright (C) 2012 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 java.util.AbstractMap;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.NavigableMap;
  import java.util.NavigableSet;
  import java.util.NoSuchElementException;
  import java.util.Set;
  import java.util.SortedMap;
  
  import javax.annotation.Nullable;
  
  /**
   * Skeletal implementation of {@link NavigableMap}.
   * 
   * @author Louis Wasserman
   */
  abstract class AbstractNavigableMap<K, V> extends AbstractMap<K, V> implements NavigableMap<K, V> {
  
    @Override
    @Nullable
    public abstract V get(@Nullable Object key);
    
    @Override
    @Nullable
    public Entry<K, V> firstEntry() {
      return Iterators.getNext(entryIterator(), null);
    }
  
    @Override
    @Nullable
    public Entry<K, V> lastEntry() {
      return Iterators.getNext(descendingEntryIterator(), null);
    }
  
    @Override
    @Nullable
    public Entry<K, V> pollFirstEntry() {
      return Iterators.pollNext(entryIterator());
    }
  
    @Override
    @Nullable
    public Entry<K, V> pollLastEntry() {
      return Iterators.pollNext(descendingEntryIterator());
    }
  
    @Override
    public K firstKey() {
      Entry<K, V> entry = firstEntry();
      if (entry == null) {
        throw new NoSuchElementException();
      } else {
        return entry.getKey();
      }
    }
  
    @Override
    public K lastKey() {
      Entry<K, V> entry = lastEntry();
      if (entry == null) {
        throw new NoSuchElementException();
      } else {
        return entry.getKey();
      }
    }
  
    @Override
    @Nullable
    public Entry<K, V> lowerEntry(K key) {
      return headMap(key, false).lastEntry();
    }
  
    @Override
    @Nullable
    public Entry<K, V> floorEntry(K key) {
      return headMap(key, true).lastEntry();
    }
  
    @Override
    @Nullable
    public Entry<K, V> ceilingEntry(K key) {
     return tailMap(key, true).firstEntry();
   }
 
   @Override
   @Nullable
   public Entry<K, V> higherEntry(K key) {
     return tailMap(key, false).firstEntry();
   }
 
   @Override
   public K lowerKey(K key) {
     return Maps.keyOrNull(lowerEntry(key));
   }
 
   @Override
   public K floorKey(K key) {
     return Maps.keyOrNull(floorEntry(key));
   }
 
   @Override
   public K ceilingKey(K key) {
     return Maps.keyOrNull(ceilingEntry(key));
   }
 
   @Override
   public K higherKey(K key) {
     return Maps.keyOrNull(higherEntry(key));
   }
 
   abstract Iterator<Entry<K, V>> entryIterator();
 
   abstract Iterator<Entry<K, V>> descendingEntryIterator();
 
   @Override
   public SortedMap<K, V> subMap(K fromKey, K toKey) {
     return subMap(fromKey, true, toKey, false);
   }
 
   @Override
   public SortedMap<K, V> headMap(K toKey) {
     return headMap(toKey, false);
   }
 
   @Override
   public SortedMap<K, V> tailMap(K fromKey) {
     return tailMap(fromKey, true);
   }
 
   @Override
   public NavigableSet<K> navigableKeySet() {
     return new Maps.NavigableKeySet<K, V>(this);
   }
 
   @Override
   public Set<K> keySet() {
     return navigableKeySet();
   }
 
   @Override
   public abstract int size();
 
   @Override
   public Set<Entry<K, V>> entrySet() {
     return new Maps.EntrySet<K, V>() {
       @Override
       Map<K, V> map() {
         return AbstractNavigableMap.this;
       }
 
       @Override
       public Iterator<Entry<K, V>> iterator() {
         return entryIterator();
       }
     };
   }
 
   @Override
   public NavigableSet<K> descendingKeySet() {
     return descendingMap().navigableKeySet();
   }
 
   @Override
   public NavigableMap<K, V> descendingMap() {
     return new DescendingMap();
   }
   
   private final class DescendingMap extends Maps.DescendingMap<K, V> {
     @Override
     NavigableMap<K, V> forward() {
       return AbstractNavigableMap.this;
     }
 
     @Override
     Iterator<Entry<K, V>> entryIterator() {
       return descendingEntryIterator();
     }
   }
 
 }