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/*
 * Copyright 2013 serso aka se.solovyev
 *
 * 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.
 *
 * ---------------------------------------------------------------------
 * Contact details
 *
 * Email: [email protected]
 * Site:  http://se.solovyev.org
 */

package org.solovyev.common.collections.multiset;

import java.util.*;

public abstract class AbstractMultiSet extends AbstractCollection implements MultiSet {

	@Override
	public boolean add(E e) {
		return this.add(e, 1);
	}

	@Override
	public boolean remove(Object o) {
		// if number of elements before was positive then remove() method call must change the collection
		return this.remove((E) o, 1) > 0;
	}

	@Override
	public boolean removeAll(Collection c) {
		boolean modified = false;

		for (Object o : c) {
			modified = modified | this.remove(o);
		}

		return modified;
	}

	@Override
	public boolean retainAll(Collection c) {
		boolean modified = false;

		for (E e : toElementSet()) {
			if (!c.contains(e)) {
				modified = modified | remove(e);
			}
		}

		return modified;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}

		if (obj instanceof MultiSet) {
			final MultiSet that = (MultiSet) obj;

			if (this.size() == that.size()) {
				boolean equals = true;

				for (E e : this) {
					if (this.count(e) != that.count(e)) {
						equals = false;
						break;
					}
				}

				return equals;
			}
		}


		return false;
	}

	@Override
	public int hashCode() {

		// not good solution but still better than nothing.
		// Problem: set doesn't require any particular order of it's elements, for equals method it is not significant information
		// however hashCode method depends on each implementation of multiset and use the order of elements returned by iterator
		// Solution (used): get all the hash codes of all elements in the multiset, sort them and then sum ()
		// Solution (not used): demand from the subclass specific order of it's elements

		final List hashCodes = new ArrayList(this.size());
		for (E e : this) {
			hashCodes.add(e == null ? 0 : e.hashCode());
		}

		Collections.sort(hashCodes);

		int result = 1;

		for (Integer hashCode : hashCodes) {
			result = 31 * result + hashCode;
		}

		return result;
	}
}