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/*
 * Copyright (c) 2013-2018 Cinchapi Inc.
 *
 * 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.
 */
package com.cinchapi.common.collect;

import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import com.google.common.collect.Iterables;
import com.google.common.collect.LinkedHashMultimap;
import com.google.common.collect.Multimap;

/**
 * Utility functions for {@link Multimap}s.
 *
 * @author Jeff Nelson
 */
public final class Multimaps {

    /**
     * Return a {@link Map} that contains the data in the {@code multimap}.
     * 
     * This method is similar to {@link Multimap#asMap()} except it will flatten
     * a value collection into a single value if the collection only contains
     * one item.
     * 
     * 
     * @param multimap
     * @return a {@link Map} with the data in the {@code multimap}
     */
    public static  Map asMapWithSingleValueWherePossible(
            Multimap multimap) {
        return multimap.asMap().entrySet().stream()
                .collect(
                        LinkedHashMap::new, (map, entry) -> map
                                .put(entry.getKey(), flatten(entry.getValue())),
                        Map::putAll);
    }

    /**
     * Return a {@link Multimap} that wraps the data in the provided
     * {@code map}.
     * 
     * NOTE: This does not create a view that reads through to
     * the original {@code map} so subsequent changes will not be reflected in
     * the returned {@link Multimap} and vice-versa.
     * 
     * 
     * @param map
     * @return the {@link Multimap}
     */
    public static  Multimap from(Map> map) {
        Multimap mmap = LinkedHashMultimap.create();
        for (Entry> entry : map.entrySet()) {
            mmap.putAll(entry.getKey(), entry.getValue());
        }
        return mmap;
    }

    /**
     * Flatten, if possible, the {@link Collection} {@code value} into a single
     * {@link Object}.
     * 
     * @param value
     * @return the "flattened" object
     */
    private static Object flatten(Collection