WeightedShuffler.java

/*
 * Copyright 2015 Lukas Tenbrink
 *
 *    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 ivorius.ivtoolkit.random;

import java.util.*;

public class WeightedShuffler
{
    public static <T extends WeightedSelector.Item> void shuffle(Random rand, List<T> items, double totalWeight)
    {
        List<WeightedSelector.SimpleItem<T>> wrapped = new ArrayList<>();

        for (T t : items)
            wrapped.add(WeightedSelector.SimpleItem.of(rand.nextDouble() * t.getWeight(), t));

        Collections.sort(wrapped, new Comparator<WeightedSelector.SimpleItem<T>>()
        {
            @Override
            public int compare(WeightedSelector.SimpleItem<T> o1, WeightedSelector.SimpleItem<T> o2)
            {
                return o1.item.getWeight() > o2.item.getWeight()
                        ? Double.compare(o1.getWeight(), o2.item.getWeight())
                        : Double.compare(o2.getWeight(), o1.item.getWeight());
            }
        });

        items.clear();
        for (WeightedSelector.SimpleItem<T> simpleItem : wrapped)
            items.add(simpleItem.item);
    }
}