org.paumard.spliterators.RollingSpliterator Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of streams-utils Show documentation
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.
There is a newer version: 2.1.1
Show newest version
/*
 * 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.concurrent.atomic.AtomicInteger;
import java.util.function.Consumer;
import java.util.stream.Stream;

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

    private final int grouping;
    private final Spliterator spliterator;
    private final Object[] buffer; // we cant create arrays of E
    private final AtomicInteger bufferWriteIndex = new AtomicInteger(0);
    private final AtomicInteger bufferReadIndex = new AtomicInteger(0);
    private boolean lastBufferSent = false;

    public static  RollingSpliterator of(Spliterator spliterator, int grouping) {
        Objects.requireNonNull(spliterator);
        if (grouping < 2) {
            throw new IllegalArgumentException("Why would you be creating a rolling spliterator with a grouping factor of less than 2?");
        }
        if ((spliterator.characteristics() & Spliterator.ORDERED) == 0) {
            throw new IllegalArgumentException("Why would you create a rolling spliterator on a non-ordered spliterator?");
        }

        return new RollingSpliterator<>(spliterator, grouping);
    }

    private RollingSpliterator(Spliterator spliterator, int grouping) {
        this.spliterator = spliterator;
        this.grouping = grouping;
        this.buffer = new Object[grouping + 1];
    }

    @Override
    public boolean tryAdvance(Consumer> action) {
        boolean hasMore = true;

        if ((bufferWriteIndex.get() == bufferReadIndex.get()) && hasMore) {
            for (int i = 0; i < grouping; i++) {
                if (!advance(this.spliterator)) {
                    hasMore = false;
                }
            }
        }
        if (!advance(spliterator)) {
            hasMore = false;
        }

        if (hasMore) {
            Stream subStream = buildSubstream();
            action.accept(subStream);
            return true;
        } else if (!lastBufferSent) {
            Stream subStream = buildSubstream();
            action.accept(subStream);
            lastBufferSent = true;
            return true;
        } else {
            return false;
        }
    }

    private boolean advance(Spliterator spliterator) {
        return spliterator.tryAdvance(
                element -> {
                    buffer[bufferWriteIndex.get() % buffer.length] = element;
                    bufferWriteIndex.incrementAndGet();
                });
    }

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

    @SuppressWarnings("unchecked")
    private Stream buildSubstream() {

        Stream.Builder subBuilder = Stream.builder();
        for (int i = 0; i < grouping; i++) {
            subBuilder.add((E) buffer[(i + bufferReadIndex.get()) % buffer.length]);
        }
        bufferReadIndex.incrementAndGet();
        return subBuilder.build();
    }

    @Override
    public long estimateSize() {
        long estimateSize = spliterator.estimateSize();
        return estimateSize == Long.MAX_VALUE ? Long.MAX_VALUE : estimateSize - grouping;
    }

    @Override
    public int characteristics() {
        // this spliterator is already ordered
        return spliterator.characteristics() & ~Spliterator.SORTED;
    }
}