/*
    * 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.hadoop.hbase.util;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.RandomAccess;
  
  /**
   * Simple sorted list implementation that uses {@link java.util.ArrayList} as
   * the underlying collection so we can support RandomAccess. All mutations
   * create a new copy of the <code>ArrayList</code> instance, so can be
   * expensive. This class is only intended for use on small, very rarely
   * written collections that expect highly concurrent reads.
   * <p>
   * Read operations are performed on a reference to the internal list at the
   * time of invocation, so will not see any mutations to the collection during
   * their operation. Iterating over list elements manually using the
   * RandomAccess pattern involves multiple operations. For this to be safe get
   * a reference to the internal list first using get(). 
   * <p>
   * If constructed with a {@link java.util.Comparator}, the list will be sorted
   * using the comparator. Adding or changing an element using an index will
   * trigger a resort.
   * <p>
   * Iterators are read-only. They cannot be used to remove elements.
   */
  @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="UG_SYNC_SET_UNSYNC_GET",
    justification="TODO: synchronization in here needs review!!!")
  public class SortedList<E> implements List<E>, RandomAccess {
    private volatile List<E> list;
    private final Comparator<? super E> comparator;
  
    /**
     * Constructs an empty list with the default initial capacity that will be
     * sorted using the given comparator.
     *
     * @param comparator the comparator
     */
    public SortedList(Comparator<? super E> comparator) {
      this.list = Collections.emptyList();
      this.comparator = comparator;
    }
  
    /**
     * Constructs a list containing the elements of the given collection, in the
     * order returned by the collection's iterator, that will be sorted with the
     * given comparator.
     *
     * @param c the collection
     * @param comparator the comparator
     */
    public SortedList(Collection<? extends E> c, Comparator<? super E> comparator) {
      this.list = Collections.unmodifiableList(new ArrayList<E>(c));
      this.comparator = comparator;
    }
  
    /**
     * Returns a reference to the unmodifiable list currently backing the SortedList.
     * Changes to the SortedList will not be reflected in this list. Use this
     * method to get a reference for iterating over using the RandomAccess
     * pattern.
     */
    public List<E> get() { // FindBugs: UG_SYNC_SET_UNSYNC_GET complaint. Fix!!
      return list;
    }
  
    @Override
    public int size() {
      return list.size();
    }
  
    @Override
    public boolean isEmpty() {
      return list.isEmpty();
    }
  
    @Override
   public boolean contains(Object o) {
     return list.contains(o);
   }
 
   @Override
   public Iterator<E> iterator() {
     return list.iterator();
   }
 
   @Override
   public Object[] toArray() {
     return list.toArray();
   }
 
   @Override
   public <T> T[] toArray(T[] a) {
     return list.toArray(a);
   }
 
   @Override
   public synchronized boolean add(E e) {
     ArrayList<E> newList = new ArrayList<E>(list);
     boolean changed = newList.add(e);
     if (changed) {
       Collections.sort(newList, comparator);
     }
     list = Collections.unmodifiableList(newList);
     return changed;
   }
 
   @Override
   public synchronized boolean remove(Object o) {
     ArrayList<E> newList = new ArrayList<E>(list);
     // Removals in ArrayList won't break sorting
     boolean changed = newList.remove(o);
     list = Collections.unmodifiableList(newList);
     return changed;
   }
 
   @Override
   public boolean containsAll(Collection<?> c) {
     return list.containsAll(c);
   }
 
   @Override
   public synchronized boolean addAll(Collection<? extends E> c) {
     ArrayList<E> newList = new ArrayList<E>(list);
     boolean changed = newList.addAll(c);
     if (changed) {
       Collections.sort(newList, comparator);
     }
     list = Collections.unmodifiableList(newList);
     return changed;
   }
 
   @Override
   public synchronized boolean addAll(int index, Collection<? extends E> c) {
     ArrayList<E> newList = new ArrayList<E>(list);
     boolean changed = newList.addAll(index, c);
     if (changed) {
       Collections.sort(newList, comparator);
     }
     list = Collections.unmodifiableList(newList);
     return changed;
   }
 
   @Override
   public synchronized boolean removeAll(Collection<?> c) {
     ArrayList<E> newList = new ArrayList<E>(list);
     // Removals in ArrayList won't break sorting
     boolean changed = newList.removeAll(c);
     list = Collections.unmodifiableList(newList);
     return changed;
   }
 
   @Override
   public synchronized boolean retainAll(Collection<?> c) {
     ArrayList<E> newList = new ArrayList<E>(list);
     // Removals in ArrayList won't break sorting
     boolean changed = newList.retainAll(c);
     list = Collections.unmodifiableList(newList);
     return changed;
   }
 
   @Override
   public synchronized void clear() {
     list = Collections.emptyList();
   }
 
   @Override
   public synchronized E get(int index) {
     return list.get(index);
   }
 
   @Override
   public synchronized E set(int index, E element) {
     ArrayList<E> newList = new ArrayList<E>(list);
     E result = newList.set(index, element);
     Collections.sort(list, comparator);
     list = Collections.unmodifiableList(newList);
     return result;
   }
 
   @Override
   public synchronized void add(int index, E element) {
     ArrayList<E> newList = new ArrayList<E>(list);
     newList.add(index, element);
     Collections.sort(list, comparator);
     list = Collections.unmodifiableList(newList);
   }
 
   @Override
   public synchronized E remove(int index) {
     ArrayList<E> newList = new ArrayList<E>(list);
     // Removals in ArrayList won't break sorting
     E result = newList.remove(index);
     list = Collections.unmodifiableList(newList);
     return result;
   }
 
   @Override
   public int indexOf(Object o) {
     return list.indexOf(o);
   }
 
   @Override
   public int lastIndexOf(Object o) {
     return list.lastIndexOf(o);
   }
 
   @Override
   public ListIterator<E> listIterator() {
     return list.listIterator();
   }
 
   @Override
   public ListIterator<E> listIterator(int index) {
     return list.listIterator(index);
   }
 
   @Override
   public List<E> subList(int fromIndex, int toIndex) {
     return list.subList(fromIndex, toIndex);
   }
 }