/**
 *
 * Copyright (c) 2006-2017, Speedment, Inc. 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.
 */
package com.speedment.runtime.core.internal.stream.parallel;

import java.util.Arrays;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Spliterator;
import java.util.function.Consumer;

import static java.util.Objects.requireNonNull;

/**
 *
 * @author pemi
 * @param <T> type of {@link Spliterator} to implement
 */
public final class ConfigurableIteratorSpliteratorImpl<T> implements Spliterator<T> {

    static final int MAX_BATCH = 1 << 25;
    private final Iterator<? extends T> iterator;
    private final int[] batchSizes;
    private final int characteristics;
    private int batchSizeIndex;
    private long sizeEstimate;

    /**
     * Creates a {@link Spliterator} using the given iterator for traversal, and
     * reporting the given initial size and characteristics.
     *
     * @param iterator the iterator for the source
     * @param size the number of elements in the source
     * @param characteristics properties of this {@link Spliterator}'s source or
     * elements.
     * @param batchSizes the batch sizes to use for pseudo parallelism
     */
    public ConfigurableIteratorSpliteratorImpl(Iterator<? extends T> iterator, long size, int characteristics, int[] batchSizes) {
        this.iterator = iterator;
        this.sizeEstimate = size;
        this.characteristics = (characteristics & Spliterator.CONCURRENT) == 0
            ? characteristics | Spliterator.SIZED | Spliterator.SUBSIZED
            : characteristics;
        this.batchSizes = Arrays.copyOf(batchSizes, batchSizes.length);
    }

    /**
     * Creates a {@link Spliterator} using the given iterator for traversal, and
     * reporting the given characteristics. The size is unknown.
     *
     * @param iterator the iterator for the source
     * @param characteristics properties of this {@link Spliterator}'s source or
     * elements.
     * @param batchSizes the batch sizes to use for pseudo parallelism
     */
    public ConfigurableIteratorSpliteratorImpl(Iterator<? extends T> iterator, int characteristics, int[] batchSizes) {
        this.iterator = iterator;
        this.sizeEstimate = Long.MAX_VALUE;
        this.characteristics = characteristics & ~(Spliterator.SIZED | Spliterator.SUBSIZED);
        this.batchSizes = Arrays.copyOf(batchSizes, batchSizes.length);
    }

    protected int nextBatchSize() {
        if (batchSizeIndex >= batchSizes.length) {
            return batchSizes[batchSizes.length - 1];
        } else {
            return batchSizes[batchSizeIndex++];
        }
    }

    @Override
    public Spliterator<T> trySplit() {
        if (sizeEstimate > 1 && iterator.hasNext()) {
            int batchSize = nextBatchSize();
            if (batchSize > sizeEstimate) {
                batchSize = (int) sizeEstimate;
            }
            if (batchSize > MAX_BATCH) {
                batchSize = MAX_BATCH;
            }
            if (batchSize == 1) {
                final T item = iterator.next();
                if (sizeEstimate != Long.MAX_VALUE) {
                    sizeEstimate--;
                }
                return new SingletonSpliterator<>(item, characteristics);
            } else {
                final Object[] array = new Object[batchSize];
                int noRead = 0;
                do {
                    array[noRead] = iterator.next();
                } while (++noRead < batchSize && iterator.hasNext());
                if (sizeEstimate != Long.MAX_VALUE) {
                    sizeEstimate -= noRead;
                }

                return new ArraySpliterator<>(array, 0, noRead, characteristics);
            }
        }
        return null;
    }

    @Override
    public void forEachRemaining(Consumer<? super T> action) {
        iterator.forEachRemaining(requireNonNull(action));
    }

    @Override
    public boolean tryAdvance(Consumer<? super T> action) {
        requireNonNull(action);
        if (iterator.hasNext()) {
            action.accept(iterator.next());
            return true;
        }
        return false;
    }

    @Override
    public long estimateSize() {
        return sizeEstimate;
    }

    @Override
    public int characteristics() {
        return characteristics;
    }

    @Override
    public Comparator<? super T> getComparator() {
        if (hasCharacteristics(Spliterator.SORTED)) {
            return null;
        }
        throw new IllegalStateException();
    }
}