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Streams Utils is a set of operations written on Java 8 Streams. It allows several basic operations that are not available in the the Java 8, and that have proven to be very useful in some cases.

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/*
 * Copyright (C) 2015 José Paumard
 *
 * 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 org.paumard.spliterators;

import org.paumard.streams.StreamsUtils;

import java.util.Objects;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.stream.IntStream;

/**
 * See the documentation and patterns to be used in this class in the {@link StreamsUtils} factory class.
 *
 * Created by José
 */
public class RepeatingSpliterator implements Spliterator {

    private final int repeating;
    private int currentRepeat = 0;
    private boolean moveToNext = true;
    private final Spliterator spliterator;
    private E currentValue;

    public static  RepeatingSpliterator of(Spliterator spliterator, int repeating) {
        Objects.requireNonNull(spliterator);
        if (repeating <= 1) {
            throw new IllegalArgumentException (("Why would you build a repeating spliterator with a repeating factor of less than 2?"));
        }
        if ((spliterator.characteristics() & Spliterator.SIZED) == 0) {
            throw new IllegalArgumentException (("Why would you try to repeat a non-SIZED spliterator?"));
        }

        return new RepeatingSpliterator<>(spliterator, repeating);
    }

    private RepeatingSpliterator(Spliterator spliterator, int repeating) {
        this.spliterator = spliterator;
        this.repeating = repeating;
    }

    @Override
    public boolean tryAdvance(Consumer action) {
        boolean hasMore = false;
        if (moveToNext) {
            hasMore = spliterator.tryAdvance(e -> {
                this.currentValue = e;
                action.accept(e);
            });
            moveToNext = false;
            currentRepeat = 1;
        } else {
            if (currentRepeat < repeating) {
                action.accept(currentValue);
                currentRepeat++;
                moveToNext = true;
                hasMore = true;
            }
        }
        return hasMore;
    }

    @Override
    public Spliterator trySplit() {
        Spliterator splitSpliterator = spliterator.trySplit();
        return splitSpliterator == null ? null : new RepeatingSpliterator<>(splitSpliterator, repeating);
    }

    @Override
    public long estimateSize() {
        long estimateSize = spliterator.estimateSize();
        return (estimateSize == Long.MAX_VALUE) || (estimateSize*repeating < estimateSize) ? Long.MAX_VALUE : estimateSize*repeating;
    }

    @Override
    public int characteristics() {
        return this.spliterator.characteristics() & ~Spliterator.SORTED | Spliterator.ORDERED;
    }
}