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SRI International's AIC Utility Library (for Java 1.6+)
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/*
 * Copyright (c) 2013, SRI International
 * All rights reserved.
 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 * 
 * http://opensource.org/licenses/BSD-3-Clause
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright
 * notice, this arrayList of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright
 * notice, this arrayList of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of the aic-expresso nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.sri.ai.util.collect;

import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.ListIterator;

import com.google.common.annotations.Beta;

/**
 * Analogous to {@link java.util.LinkedHashSet}, but with an {@link java.util.ArrayList} instead of a {@link java.util.LinkedList},
 * offering the same advantages (random access) and disadvantages (slower addition and removal of elements),
 * but with the extra advantage of offering an iterator that is actually a {@link java.util.ListIterator}.
 * @author braz
 *
 * @param  the type of the elements
 */
@Beta
public class ArrayHashSet extends AbstractSet implements ArraySet {

	private HashSet   set;
	private ArrayList arrayList;
	
	public ArrayHashSet() {
		this.set  = new HashSet();
		this.arrayList = new ArrayList();
	}
	
	public ArrayHashSet(int capacity) {
		this.set  = new HashSet();
		this.arrayList = new ArrayList(capacity);
	}
	
	public ArrayHashSet(Collection collection) {
		this();
		addAll(collection);
	}
	
	// ArraySet methods
	
	@Override
	public ArrayHashSetIterator listIterator() {
		return new ArrayHashSetIterator(arrayList.listIterator());
	}

	@Override
	public ArrayHashSetIterator listIterator(int index) {
		return new ArrayHashSetIterator(arrayList.listIterator(index));
	}

	@Override
	public E get(int index) {
		return listIterator(index).next();
	}

	@Override
	public void set(int index, E element) {
		ArrayHashSet.ArrayHashSetIterator listIterator = listIterator(index);
		listIterator.next();
		listIterator.set(element);
	}

	// end of ArraySet methods
	
	// required implementations
	
	@Override
	public boolean add(E element) {
		boolean modified = set.add(element);
		if (modified) {
			arrayList.add(element);
		}
		return modified;
	}

	@Override
	public ArrayHashSetIterator iterator() {
		return new ArrayHashSetIterator(arrayList.listIterator());
	}

	@Override
	public int size() {
		return set.size();
	}
	
	// end of required implementations

	// methods not required to be implemented, but more efficient
	
	@Override
	public boolean contains(Object o) {
		return set.contains(o);
	}
	
	@Override
	public Object[] toArray() {
		return arrayList.toArray();
	}
	
	@Override
	public  T[] toArray(T[] a) {
		return arrayList.toArray(a);
	}
	
	@Override
	public boolean remove(Object o) {
		boolean removed = set.remove(o);
		if (removed) {
			arrayList.remove(o);
		}
		return removed;
	}
	
	@Override
	public void clear() {
		set.clear();
		arrayList.clear();
	}
	
	// end of methods not required to be implemented, but more efficient

	private class ArrayHashSetIterator implements ListIterator {

		private ListIterator arrayListIterator;
		private E lastElementProvided;
		
		public ArrayHashSetIterator(ListIterator arrayListIterator) {
			this.arrayListIterator = arrayListIterator;
		}
		
		@Override
		public boolean hasNext() {
			return arrayListIterator.hasNext();
		}

		@Override
		public E next() {
			return lastElementProvided = arrayListIterator.next();
		}

		@Override
		public void add(E element) {
			if (set.add(element)) {
				arrayListIterator.add(element);
			}
		}

		@Override
		public boolean hasPrevious() {
			return arrayListIterator.hasPrevious();
		}

		@Override
		public int nextIndex() {
			return arrayListIterator.nextIndex();
		}

		@Override
		public E previous() {
			return lastElementProvided = arrayListIterator.previous();
		}

		@Override
		public int previousIndex() {
			return arrayListIterator.previousIndex();
		}

		@Override
		public void remove() {
			arrayListIterator.remove();
			set.remove(lastElementProvided);
		}

		@Override
		public void set(E element) {
			if (element.equals(lastElementProvided)) {
				// no need to do anything
			}
			else {
				if (set.contains(element)) {
					// cannot add because element would appear more than once
					throw new IllegalArgumentException("Cannot set already-present element in a different position in ArrayHashSet.");
				}
				else {
					arrayListIterator.set(element);
					set.remove(lastElementProvided);
					set.add(element);
				}
			}
		}
	}
}