/*-
 * ============LICENSE_START=======================================================
 * VID
 * ================================================================================
 * Copyright (C) 2017 AT&T Intellectual Property. All rights reserved.
 * Modifications Copyright (C) 2018 Nokia. All rights reserved.
 * ================================================================================
 * 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.
 * ============LICENSE_END=========================================================
 */

package org.onap.vid.utils;

import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;


public class Intersection {
    private Intersection() {
    }

    /**
     * Returns intersection of given lists. Treats those lists as sets, ignores repetitions.
     */
    public static <T> List<T> of(Collection<List<T>> lists) {
        return lists
                .stream()
                .map(elements -> (Set<T>) Sets.newHashSet(elements))
                .reduce(Sets::intersection)
                .map(set -> (List<T>) Lists.newArrayList(set))
                .orElse(Collections.emptyList());
    }
}