/*
 *  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.tools.ant.types.resources;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.types.Resource;
import org.apache.tools.ant.types.ResourceCollection;

/**
 * ResourceCollection representing the difference between
 * two or more nested ResourceCollections.
 * @since Ant 1.7
 */
public class Difference extends BaseResourceCollectionContainer {

    /**
     * Calculate the difference of the nested ResourceCollections.
     * @return a Collection of Resources.
     */
    @Override
    protected Collection<Resource> getCollection() {
        List<ResourceCollection> rcs = getResourceCollections();
        int size = rcs.size();
        if (size < 2) {
            throw new BuildException(
                "The difference of %d resource %s is undefined.", size,
                size == 1 ? "collection" : "collections");
        }
        Set<Resource> hs = new HashSet<>();
        List<Resource> al = new ArrayList<>();
        for (ResourceCollection rc : rcs) {
            for (Resource r : rc) {
                if (hs.add(r)) {
                    al.add(r);
                } else {
                    al.remove(r);
                }
            }
        }
        return al;
    }

}