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/*
 * Copyright (C) 2016 HaiYang Li
 *
 * 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.landawn.abacus.util.stream;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.Callable;

import com.landawn.abacus.util.CompletableFuture;
import com.landawn.abacus.util.IndexedInt;
import com.landawn.abacus.util.IntIterator;
import com.landawn.abacus.util.IntList;
import com.landawn.abacus.util.IntSummaryStatistics;
import com.landawn.abacus.util.LongMultiset;
import com.landawn.abacus.util.Multimap;
import com.landawn.abacus.util.Multiset;
import com.landawn.abacus.util.MutableBoolean;
import com.landawn.abacus.util.MutableLong;
import com.landawn.abacus.util.N;
import com.landawn.abacus.util.Nth;
import com.landawn.abacus.util.NullabLe;
import com.landawn.abacus.util.OptionalDouble;
import com.landawn.abacus.util.OptionalInt;
import com.landawn.abacus.util.Holder;
import com.landawn.abacus.util.Pair;
import com.landawn.abacus.util.function.BiConsumer;
import com.landawn.abacus.util.function.BiFunction;
import com.landawn.abacus.util.function.BinaryOperator;
import com.landawn.abacus.util.function.Consumer;
import com.landawn.abacus.util.function.Function;
import com.landawn.abacus.util.function.IntBiFunction;
import com.landawn.abacus.util.function.IntBinaryOperator;
import com.landawn.abacus.util.function.IntConsumer;
import com.landawn.abacus.util.function.IntFunction;
import com.landawn.abacus.util.function.IntPredicate;
import com.landawn.abacus.util.function.IntToByteFunction;
import com.landawn.abacus.util.function.IntToCharFunction;
import com.landawn.abacus.util.function.IntToDoubleFunction;
import com.landawn.abacus.util.function.IntToFloatFunction;
import com.landawn.abacus.util.function.IntToLongFunction;
import com.landawn.abacus.util.function.IntToShortFunction;
import com.landawn.abacus.util.function.IntTriFunction;
import com.landawn.abacus.util.function.IntUnaryOperator;
import com.landawn.abacus.util.function.ObjIntConsumer;
import com.landawn.abacus.util.function.Predicate;
import com.landawn.abacus.util.function.Supplier;
import com.landawn.abacus.util.function.ToByteFunction;
import com.landawn.abacus.util.function.ToCharFunction;
import com.landawn.abacus.util.function.ToDoubleFunction;
import com.landawn.abacus.util.function.ToFloatFunction;
import com.landawn.abacus.util.function.ToIntFunction;
import com.landawn.abacus.util.function.ToLongFunction;
import com.landawn.abacus.util.function.ToShortFunction;

/**
 * This class is a sequential, stateful and immutable stream implementation.
 *
 * @since 0.8
 * 
 * @author Haiyang Li
 */
final class ParallelIteratorIntStream extends IteratorIntStream {
    private final int maxThreadNum;
    private final Splitor splitor;
    private volatile IteratorIntStream sequential;
    private volatile Stream boxed;

    ParallelIteratorIntStream(final IntIterator values, final Collection closeHandlers, final boolean sorted, final int maxThreadNum,
            final Splitor splitor) {
        super(values, closeHandlers, sorted);

        this.maxThreadNum = N.min(maxThreadNum, MAX_THREAD_NUM_PER_OPERATION);
        this.splitor = splitor == null ? DEFAULT_SPLITOR : splitor;
    }

    ParallelIteratorIntStream(final IntStream stream, final Set closeHandlers, final boolean sorted, final int maxThreadNum, final Splitor splitor) {
        this(stream.exIterator(), mergeCloseHandlers(stream, closeHandlers), sorted, maxThreadNum, splitor);
    }

    ParallelIteratorIntStream(final Stream stream, final Set closeHandlers, final boolean sorted, final int maxThreadNum,
            final Splitor splitor) {
        this(intIterator(stream.exIterator()), mergeCloseHandlers(stream, closeHandlers), sorted, maxThreadNum, splitor);
    }

    @Override
    public IntStream filter(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().filter(predicate).exIterator(), closeHandlers, sorted, maxThreadNum, splitor);
        }

        final Stream stream = boxed().filter(new Predicate() {
            @Override
            public boolean test(Integer value) {
                return predicate.test(value);
            }
        });

        return new ParallelIteratorIntStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream takeWhile(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().takeWhile(predicate).exIterator(), closeHandlers, sorted, maxThreadNum, splitor);
        }

        final Stream stream = boxed().takeWhile(new Predicate() {
            @Override
            public boolean test(Integer value) {
                return predicate.test(value);
            }
        });

        return new ParallelIteratorIntStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream dropWhile(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().dropWhile(predicate).exIterator(), closeHandlers, sorted, maxThreadNum, splitor);
        }

        final Stream stream = boxed().dropWhile(new Predicate() {
            @Override
            public boolean test(Integer value) {
                return predicate.test(value);
            }
        });

        return new ParallelIteratorIntStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream map(final IntUnaryOperator mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().map(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final IntStream stream = boxed().mapToInt(new ToIntFunction() {
            @Override
            public int applyAsInt(Integer value) {
                return mapper.applyAsInt(value);
            }
        });

        return new ParallelIteratorIntStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public CharStream mapToChar(final IntToCharFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorCharStream(sequential().mapToChar(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final CharStream stream = boxed().mapToChar(new ToCharFunction() {
            @Override
            public char applyAsChar(Integer value) {
                return mapper.applyAsChar(value);
            }
        });

        return new ParallelIteratorCharStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public ByteStream mapToByte(final IntToByteFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorByteStream(sequential().mapToByte(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final ByteStream stream = boxed().mapToByte(new ToByteFunction() {
            @Override
            public byte applyAsByte(Integer value) {
                return mapper.applyAsByte(value);
            }
        });

        return new ParallelIteratorByteStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public ShortStream mapToShort(final IntToShortFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorShortStream(sequential().mapToShort(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final ShortStream stream = boxed().mapToShort(new ToShortFunction() {
            @Override
            public short applyAsShort(Integer value) {
                return mapper.applyAsShort(value);
            }
        });

        return new ParallelIteratorShortStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public LongStream mapToLong(final IntToLongFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorLongStream(sequential().mapToLong(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final LongStream stream = boxed().mapToLong(new ToLongFunction() {
            @Override
            public long applyAsLong(Integer value) {
                return mapper.applyAsLong(value);
            }
        });

        return new ParallelIteratorLongStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public FloatStream mapToFloat(final IntToFloatFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorFloatStream(sequential().mapToFloat(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final FloatStream stream = boxed().mapToFloat(new ToFloatFunction() {
            @Override
            public float applyAsFloat(Integer value) {
                return mapper.applyAsFloat(value);
            }
        });

        return new ParallelIteratorFloatStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public DoubleStream mapToDouble(final IntToDoubleFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorDoubleStream(sequential().mapToDouble(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final DoubleStream stream = boxed().mapToDouble(new ToDoubleFunction() {
            @Override
            public double applyAsDouble(Integer value) {
                return mapper.applyAsDouble(value);
            }
        });

        return new ParallelIteratorDoubleStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public  Stream mapToObj(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorStream<>(sequential().mapToObj(mapper).iterator(), closeHandlers, false, null, maxThreadNum, splitor);
        }

        return boxed().map(new Function() {
            @Override
            public U apply(Integer value) {
                return mapper.apply(value);
            }
        });
    }

    @Override
    public IntStream flatMap(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().flatMap(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final IntStream stream = boxed().flatMapToInt(new Function() {
            @Override
            public IntStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorIntStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public CharStream flatMapToChar(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorCharStream(sequential().flatMapToChar(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final CharStream stream = boxed().flatMapToChar(new Function() {
            @Override
            public CharStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorCharStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public ByteStream flatMapToByte(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorByteStream(sequential().flatMapToByte(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final ByteStream stream = boxed().flatMapToByte(new Function() {
            @Override
            public ByteStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorByteStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public ShortStream flatMapToShort(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorShortStream(sequential().flatMapToShort(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final ShortStream stream = boxed().flatMapToShort(new Function() {
            @Override
            public ShortStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorShortStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public LongStream flatMapToLong(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorLongStream(sequential().flatMapToLong(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final LongStream stream = boxed().flatMapToLong(new Function() {
            @Override
            public LongStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorLongStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public FloatStream flatMapToFloat(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorFloatStream(sequential().flatMapToFloat(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final FloatStream stream = boxed().flatMapToFloat(new Function() {
            @Override
            public FloatStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorFloatStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public DoubleStream flatMapToDouble(final IntFunction mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorDoubleStream(sequential().flatMapToDouble(mapper).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final DoubleStream stream = boxed().flatMapToDouble(new Function() {
            @Override
            public DoubleStream apply(Integer value) {
                return mapper.apply(value);
            }
        });

        return new ParallelIteratorDoubleStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public  Stream flatMapToObj(final IntFunction> mapper) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorStream<>(sequential().flatMapToObj(mapper).iterator(), closeHandlers, false, null, maxThreadNum, splitor);
        }

        return boxed().flatMap(new Function>() {
            @Override
            public Stream apply(Integer value) {
                return mapper.apply(value);
            }
        });
    }

    @Override
    public Stream split(final int size) {
        return new ParallelIteratorStream<>(sequential().split(size).iterator(), closeHandlers, false, null, maxThreadNum, splitor);
    }

    @Override
    public Stream splitToList(final int size) {
        return new ParallelIteratorStream<>(sequential().splitToList(size).iterator(), closeHandlers, false, null, maxThreadNum, splitor);
    }

    @Override
    public  Stream split(final U identity, final BiFunction predicate,
            final Consumer identityUpdate) {
        return new ParallelIteratorStream<>(sequential().split(identity, predicate, identityUpdate).iterator(), closeHandlers, false, null, maxThreadNum,
                splitor);
    }

    @Override
    public  Stream splitToList(final U identity, final BiFunction predicate,
            final Consumer identityUpdate) {
        return new ParallelIteratorStream<>(sequential().splitToList(identity, predicate, identityUpdate).iterator(), closeHandlers, false, null, maxThreadNum,
                splitor);
    }

    @Override
    public Stream splitBy(final IntPredicate where) {
        N.requireNonNull(where);

        final List testedElements = new ArrayList<>();

        final NullabLe first = indexed().findFirst(new Predicate() {
            @Override
            public boolean test(IndexedInt indexed) {
                synchronized (testedElements) {
                    testedElements.add(indexed);
                }

                return !where.test(indexed.value());
            }
        });

        N.sort(testedElements, INDEXED_INT_COMPARATOR);

        final int n = first.isPresent() ? (int) first.get().index() : testedElements.size();

        final IntList list1 = new IntList(n);
        final IntList list2 = new IntList(testedElements.size() - n);

        for (int i = 0; i < n; i++) {
            list1.add(testedElements.get(i).value());
        }

        for (int i = n, size = testedElements.size(); i < size; i++) {
            list2.add(testedElements.get(i).value());
        }

        final IntStream[] a = new IntStream[2];
        a[0] = new ArrayIntStream(list1.array(), null, sorted);
        a[1] = new IteratorIntStream(elements, null, sorted);

        if (N.notNullOrEmpty(list2)) {
            if (sorted) {
                a[1] = new IteratorIntStream(a[1].prepend(list2.stream()).exIterator(), null, sorted);
            } else {
                a[1] = a[1].prepend(list2.stream());
            }
        }

        return new ParallelArrayStream<>(a, 0, a.length, closeHandlers, false, null, maxThreadNum, splitor);
    }

    @Override
    public Stream sliding(final int windowSize, final int increment) {
        return new ParallelIteratorStream<>(sequential().sliding(windowSize, increment).iterator(), closeHandlers, false, null, maxThreadNum, splitor);
    }

    @Override
    public Stream slidingToList(final int windowSize, final int increment) {
        return new ParallelIteratorStream<>(sequential().slidingToList(windowSize, increment).iterator(), closeHandlers, false, null, maxThreadNum, splitor);
    }

    @Override
    public IntStream top(int n) {
        return top(n, INT_COMPARATOR);
    }

    @Override
    public IntStream top(int n, Comparator comparator) {
        return new ParallelIteratorIntStream(this.sequential().top(n, comparator).exIterator(), closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public IntStream sorted() {
        if (sorted) {
            return this;
        }

        return new ParallelIteratorIntStream(new ExIntIterator() {
            int[] a = null;
            int toIndex = 0;
            int cursor = 0;

            @Override
            public boolean hasNext() {
                if (a == null) {
                    sort();
                }

                return cursor < toIndex;
            }

            @Override
            public int nextInt() {
                if (a == null) {
                    sort();
                }

                if (cursor >= toIndex) {
                    throw new NoSuchElementException();
                }

                return a[cursor++];
            }

            @Override
            public long count() {
                if (a == null) {
                    sort();
                }

                return toIndex - cursor;
            }

            @Override
            public void skip(long n) {
                if (a == null) {
                    sort();
                }

                cursor = n < toIndex - cursor ? cursor + (int) n : toIndex;
            }

            @Override
            public int[] toArray() {
                if (a == null) {
                    sort();
                }

                if (cursor == 0) {
                    return a;
                } else {
                    return N.copyOfRange(a, cursor, toIndex);
                }
            }

            private void sort() {
                a = elements.toArray();
                toIndex = a.length;

                N.parallelSort(a);
            }
        }, closeHandlers, true, maxThreadNum, splitor);
    }

    @Override
    public IntStream peek(final IntConsumer action) {
        if (maxThreadNum <= 1) {
            return new ParallelIteratorIntStream(sequential().peek(action).exIterator(), closeHandlers, false, maxThreadNum, splitor);
        }

        final IntStream stream = boxed().peek(new Consumer() {
            @Override
            public void accept(Integer t) {
                action.accept(t);
            }
        }).sequential().mapToInt(ToIntFunction.UNBOX);

        return new ParallelIteratorIntStream(stream, closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream limit(final long maxSize) {
        if (maxSize < 0) {
            throw new IllegalArgumentException("'maxSize' can't be negative: " + maxSize);
        }

        return new ParallelIteratorIntStream(new ExIntIterator() {
            private long cnt = 0;

            @Override
            public boolean hasNext() {
                return cnt < maxSize && elements.hasNext();
            }

            @Override
            public int nextInt() {
                if (cnt >= maxSize) {
                    throw new NoSuchElementException();
                }

                cnt++;
                return elements.nextInt();
            }

            @Override
            public void skip(long n) {
                elements.skip(n);
            }
        }, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public IntStream skip(final long n) {
        if (n < 0) {
            throw new IllegalArgumentException("The skipped number can't be negative: " + n);
        } else if (n == 0) {
            return this;
        }

        return new ParallelIteratorIntStream(new ExIntIterator() {
            private boolean skipped = false;

            @Override
            public boolean hasNext() {
                if (skipped == false) {
                    elements.skip(n);
                    skipped = true;
                }

                return elements.hasNext();
            }

            @Override
            public int nextInt() {
                if (skipped == false) {
                    elements.skip(n);
                    skipped = true;
                }

                return elements.nextInt();
            }

            @Override
            public long count() {
                if (skipped == false) {
                    elements.skip(n);
                    skipped = true;
                }

                return elements.count();
            }

            @Override
            public void skip(long n2) {
                if (skipped == false) {
                    elements.skip(n);
                    skipped = true;
                }

                elements.skip(n2);
            }

            @Override
            public int[] toArray() {
                if (skipped == false) {
                    elements.skip(n);
                    skipped = true;
                }

                return elements.toArray();
            }
        }, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public void forEach(final IntConsumer action) {
        if (maxThreadNum <= 1) {
            sequential().forEach(action);
            return;
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    int next = 0;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            action.accept(next);
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);
    }

    @Override
    public int[] toArray() {
        return elements.toArray();
    }

    @Override
    public IntList toIntList() {
        return IntList.of(toArray());
    }

    @Override
    public List toList() {
        final List result = new ArrayList<>();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public > R toList(Supplier supplier) {
        final R result = supplier.get();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public Set toSet() {
        final Set result = new HashSet<>();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public > R toSet(Supplier supplier) {
        final R result = supplier.get();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public Multiset toMultiset() {
        final Multiset result = new Multiset<>();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public Multiset toMultiset(Supplier> supplier) {
        final Multiset result = supplier.get();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public LongMultiset toLongMultiset() {
        final LongMultiset result = new LongMultiset<>();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public LongMultiset toLongMultiset(Supplier> supplier) {
        final LongMultiset result = supplier.get();

        while (elements.hasNext()) {
            result.add(elements.nextInt());
        }

        return result;
    }

    @Override
    public > M toMap(final IntFunction keyExtractor, final IntFunction valueMapper,
            final BinaryOperator mergeFunction, final Supplier mapFactory) {
        if (maxThreadNum <= 1) {
            return sequential().toMap(keyExtractor, valueMapper, mergeFunction, mapFactory);
        }

        final Function keyExtractor2 = new Function() {
            @Override
            public K apply(Integer value) {
                return keyExtractor.apply(value);
            }
        };

        final Function valueMapper2 = new Function() {
            @Override
            public U apply(Integer value) {
                return valueMapper.apply(value);
            }
        };

        return boxed().toMap(keyExtractor2, valueMapper2, mergeFunction, mapFactory);
    }

    @Override
    public > M toMap(final IntFunction classifier, final Collector downstream,
            final Supplier mapFactory) {
        if (maxThreadNum <= 1) {
            return sequential().toMap(classifier, downstream, mapFactory);
        }

        final Function classifier2 = new Function() {
            @Override
            public K apply(Integer value) {
                return classifier.apply(value);
            }
        };

        return boxed().toMap(classifier2, downstream, mapFactory);
    }

    @Override
    public > Multimap toMultimap(final IntFunction keyExtractor, final IntFunction valueMapper,
            final Supplier> mapFactory) {
        if (maxThreadNum <= 1) {
            return sequential().toMultimap(keyExtractor, valueMapper, mapFactory);
        }

        final Function keyExtractor2 = new Function() {
            @Override
            public K apply(Integer value) {
                return keyExtractor.apply(value);
            }
        };

        final Function valueMapper2 = new Function() {
            @Override
            public U apply(Integer value) {
                return valueMapper.apply(value);
            }
        };

        return boxed().toMultimap(keyExtractor2, valueMapper2, mapFactory);
    }

    @Override
    public int reduce(final int identity, final IntBinaryOperator op) {
        if (maxThreadNum <= 1) {
            return sequential().reduce(identity, op);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public Integer call() {
                    int result = identity;
                    int next = 0;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            result = op.applyAsInt(result, next);
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }

                    return result;
                }
            }));
        }

        if (eHolder.value() != null) {
            throw N.toRuntimeException(eHolder.value());
        }

        Integer result = null;

        try {
            for (CompletableFuture future : futureList) {
                if (result == null) {
                    result = future.get();
                } else {
                    result = op.applyAsInt(result, future.get());
                }
            }
        } catch (Exception e) {
            throw N.toRuntimeException(e);
        }

        return result == null ? identity : result;
    }

    @Override
    public OptionalInt reduce(final IntBinaryOperator accumulator) {
        if (maxThreadNum <= 1) {
            return sequential().reduce(accumulator);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public Integer call() {
                    int result = 0;

                    synchronized (elements) {
                        if (elements.hasNext()) {
                            result = elements.nextInt();
                        } else {
                            return null;
                        }
                    }

                    int next = 0;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            result = accumulator.applyAsInt(result, next);
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }

                    return result;
                }
            }));
        }

        if (eHolder.value() != null) {
            throw N.toRuntimeException(eHolder.value());
        }

        Integer result = null;

        try {
            for (CompletableFuture future : futureList) {
                final Integer tmp = future.get();

                if (tmp == null) {
                    continue;
                } else if (result == null) {
                    result = tmp;
                } else {
                    result = accumulator.applyAsInt(result, tmp);
                }
            }
        } catch (Exception e) {
            throw N.toRuntimeException(e);
        }

        return result == null ? OptionalInt.empty() : OptionalInt.of(result);
    }

    @Override
    public  R collect(final Supplier supplier, final ObjIntConsumer accumulator, final BiConsumer combiner) {
        if (maxThreadNum <= 1) {
            return sequential().collect(supplier, accumulator, combiner);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Callable() {
                @Override
                public R call() {
                    final R container = supplier.get();
                    int next = 0;

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            accumulator.accept(container, next);
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }

                    return container;
                }
            }));
        }

        if (eHolder.value() != null) {
            throw N.toRuntimeException(eHolder.value());
        }

        R container = (R) NONE;

        try {
            for (CompletableFuture future : futureList) {
                if (container == NONE) {
                    container = future.get();
                } else {
                    combiner.accept(container, future.get());
                }
            }
        } catch (Exception e) {
            throw N.toRuntimeException(e);
        }

        return container == NONE ? supplier.get() : container;
    }

    @Override
    public OptionalInt head() {
        if (head == null) {
            head = elements.hasNext() ? OptionalInt.of(elements.nextInt()) : OptionalInt.empty();
            tail = new ParallelIteratorIntStream(elements, closeHandlers, sorted, maxThreadNum, splitor);
        }

        return head;
    }

    @Override
    public IntStream tail() {
        if (tail == null) {
            head = elements.hasNext() ? OptionalInt.of(elements.nextInt()) : OptionalInt.empty();
            tail = new ParallelIteratorIntStream(elements, closeHandlers, sorted, maxThreadNum, splitor);
        }

        return tail;
    }

    @Override
    public IntStream head2() {
        if (head2 == null) {
            final int[] a = elements.toArray();
            head2 = new ParallelArrayIntStream(a, 0, a.length == 0 ? 0 : a.length - 1, closeHandlers, sorted, maxThreadNum, splitor);
            tail2 = a.length == 0 ? OptionalInt.empty() : OptionalInt.of(a[a.length - 1]);
        }

        return head2;
    }

    @Override
    public OptionalInt tail2() {
        if (tail2 == null) {
            final int[] a = elements.toArray();
            head2 = new ParallelArrayIntStream(a, 0, a.length == 0 ? 0 : a.length - 1, closeHandlers, sorted, maxThreadNum, splitor);
            tail2 = a.length == 0 ? OptionalInt.empty() : OptionalInt.of(a[a.length - 1]);
        }

        return tail2;
    }

    @Override
    public OptionalInt min() {
        if (elements.hasNext() == false) {
            return OptionalInt.empty();
        } else if (sorted) {
            return OptionalInt.of(elements.nextInt());
        }

        int candidate = elements.nextInt();
        int next = 0;

        while (elements.hasNext()) {
            next = elements.nextInt();

            if (N.compare(next, candidate) < 0) {
                candidate = next;
            }
        }

        return OptionalInt.of(candidate);
    }

    @Override
    public OptionalInt max() {
        if (elements.hasNext() == false) {
            return OptionalInt.empty();
        } else if (sorted) {
            int next = 0;

            while (elements.hasNext()) {
                next = elements.nextInt();
            }

            return OptionalInt.of(next);
        }

        int candidate = elements.nextInt();
        int next = 0;

        while (elements.hasNext()) {
            next = elements.nextInt();

            if (N.compare(next, candidate) > 0) {
                candidate = next;
            }
        }

        return OptionalInt.of(candidate);
    }

    @Override
    public OptionalInt kthLargest(int k) {
        N.checkArgument(k > 0, "'k' must be bigger than 0");

        if (elements.hasNext() == false) {
            return OptionalInt.empty();
        }

        final NullabLe optional = boxed().kthLargest(k, INT_COMPARATOR);

        return optional.isPresent() ? OptionalInt.of(optional.get()) : OptionalInt.empty();
    }

    @Override
    public long sum() {
        long result = 0;

        while (elements.hasNext()) {
            result += elements.nextInt();
        }

        return result;
    }

    @Override
    public OptionalDouble average() {
        if (elements.hasNext() == false) {
            return OptionalDouble.empty();
        }

        return sequential().average();
    }

    @Override
    public long count() {
        return elements.count();
    }

    @Override
    public IntSummaryStatistics summarize() {
        final IntSummaryStatistics result = new IntSummaryStatistics();

        while (elements.hasNext()) {
            result.accept(elements.nextInt());
        }

        return result;
    }

    @Override
    public boolean anyMatch(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return sequential().anyMatch(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final MutableBoolean result = MutableBoolean.of(false);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    int next = 0;

                    try {
                        while (result.isFalse() && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                result.setTrue();
                                break;
                            }
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);

        return result.value();
    }

    @Override
    public boolean allMatch(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return sequential().allMatch(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final MutableBoolean result = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    int next = 0;

                    try {
                        while (result.isTrue() && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next) == false) {
                                result.setFalse();
                                break;
                            }
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);

        return result.value();
    }

    @Override
    public boolean noneMatch(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return sequential().noneMatch(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final MutableBoolean result = MutableBoolean.of(true);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    int next = 0;

                    try {
                        while (result.isTrue() && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                result.setFalse();
                                break;
                            }
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);

        return result.value();
    }

    @Override
    public OptionalInt findFirst(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return sequential().findFirst(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder> resultHolder = new Holder<>();
        final MutableLong index = MutableLong.of(0);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    final Pair pair = new Pair<>();

                    try {
                        while (resultHolder.value() == null && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    pair.left = index.getAndIncrement();
                                    pair.right = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(pair.right)) {
                                synchronized (resultHolder) {
                                    if (resultHolder.value() == null || pair.left < resultHolder.value().left) {
                                        resultHolder.setValue(pair.copy());
                                    }
                                }

                                break;
                            }
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);

        return resultHolder.value() == null ? OptionalInt.empty() : OptionalInt.of(resultHolder.value().right);
    }

    @Override
    public OptionalInt findLast(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return sequential().findLast(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder> resultHolder = new Holder<>();
        final MutableLong index = MutableLong.of(0);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    final Pair pair = new Pair<>();

                    try {
                        while (eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    pair.left = index.getAndIncrement();
                                    pair.right = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(pair.right)) {
                                synchronized (resultHolder) {
                                    if (resultHolder.value() == null || pair.left > resultHolder.value().left) {
                                        resultHolder.setValue(pair.copy());
                                    }
                                }
                            }
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);

        return resultHolder.value() == null ? OptionalInt.empty() : OptionalInt.of(resultHolder.value().right);
    }

    @Override
    public OptionalInt findAny(final IntPredicate predicate) {
        if (maxThreadNum <= 1) {
            return sequential().findAny(predicate);
        }

        final List> futureList = new ArrayList<>(maxThreadNum);
        final Holder eHolder = new Holder<>();
        final Holder resultHolder = Holder.of(NONE);

        for (int i = 0; i < maxThreadNum; i++) {
            futureList.add(asyncExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    int next = 0;

                    try {
                        while (resultHolder.value() == NONE && eHolder.value() == null) {
                            synchronized (elements) {
                                if (elements.hasNext()) {
                                    next = elements.nextInt();
                                } else {
                                    break;
                                }
                            }

                            if (predicate.test(next)) {
                                synchronized (resultHolder) {
                                    if (resultHolder.value() == NONE) {
                                        resultHolder.setValue(next);
                                    }
                                }

                                break;
                            }
                        }
                    } catch (Throwable e) {
                        setError(eHolder, e);
                    }
                }
            }));
        }

        complete(futureList, eHolder);

        return resultHolder.value() == NONE ? OptionalInt.empty() : OptionalInt.of((Integer) resultHolder.value());
    }

    @Override
    public LongStream asLongStream() {
        return new ParallelIteratorLongStream(new ExLongIterator() {
            @Override
            public boolean hasNext() {
                return elements.hasNext();
            }

            @Override
            public long nextLong() {
                return elements.nextInt();
            }

            @Override
            public long count() {
                return elements.count();
            }

            @Override
            public void skip(long n) {
                elements.skip(n);
            }
        }, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public FloatStream asFloatStream() {
        return new ParallelIteratorFloatStream(new ExFloatIterator() {
            @Override
            public boolean hasNext() {
                return elements.hasNext();
            }

            @Override
            public float nextFloat() {
                return elements.nextInt();
            }

            @Override
            public long count() {
                return elements.count();
            }

            @Override
            public void skip(long n) {
                elements.skip(n);
            }
        }, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public DoubleStream asDoubleStream() {
        return new ParallelIteratorDoubleStream(new ExDoubleIterator() {
            @Override
            public boolean hasNext() {
                return elements.hasNext();
            }

            @Override
            public double nextDouble() {
                return elements.nextInt();
            }

            @Override
            public long count() {
                return elements.count();
            }

            @Override
            public void skip(long n) {
                elements.skip(n);
            }
        }, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public Stream boxed() {
        Stream tmp = boxed;

        if (tmp == null) {
            tmp = new ParallelIteratorStream<>(iterator(), closeHandlers, sorted, sorted ? INT_COMPARATOR : null, maxThreadNum, splitor);
            boxed = tmp;
        }

        return tmp;
    }

    @Override
    public IntStream append(IntStream stream) {
        return new ParallelIteratorIntStream(IntStream.concat(this, stream), closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream prepend(IntStream stream) {
        return new ParallelIteratorIntStream(IntStream.concat(stream, this), closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream merge(final IntStream b, final IntBiFunction nextSelector) {
        return new ParallelIteratorIntStream(IntStream.merge(this, b, nextSelector), closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream zipWith(IntStream b, IntBiFunction zipFunction) {
        return new ParallelIteratorIntStream(IntStream.zip(this, b, zipFunction), closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream zipWith(IntStream b, IntStream c, IntTriFunction zipFunction) {
        return new ParallelIteratorIntStream(IntStream.zip(this, b, c, zipFunction), closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream zipWith(IntStream b, int valueForNoneA, int valueForNoneB, IntBiFunction zipFunction) {
        return new ParallelIteratorIntStream(IntStream.zip(this, b, valueForNoneA, valueForNoneB, zipFunction), closeHandlers, false, maxThreadNum, splitor);
    }

    @Override
    public IntStream zipWith(IntStream b, IntStream c, int valueForNoneA, int valueForNoneB, int valueForNoneC, IntTriFunction zipFunction) {
        return new ParallelIteratorIntStream(IntStream.zip(this, b, c, valueForNoneA, valueForNoneB, valueForNoneC, zipFunction), closeHandlers, false,
                maxThreadNum, splitor);
    }

    @Override
    public boolean isParallel() {
        return true;
    }

    @Override
    public IntStream sequential() {
        IteratorIntStream tmp = sequential;

        if (tmp == null) {
            tmp = new IteratorIntStream(elements, closeHandlers, sorted);
            sequential = tmp;
        }

        return tmp;
    }

    @Override
    public IntStream parallel(int maxThreadNum, Splitor splitor) {
        if (maxThreadNum < 1 || maxThreadNum > MAX_THREAD_NUM_PER_OPERATION) {
            throw new IllegalArgumentException("'maxThreadNum' must not less than 1 or exceeded: " + MAX_THREAD_NUM_PER_OPERATION);
        }

        if (this.maxThreadNum == maxThreadNum && this.splitor == splitor) {
            return this;
        }

        return new ParallelIteratorIntStream(elements, closeHandlers, sorted, maxThreadNum, splitor);
    }

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

    @Override
    public IntStream maxThreadNum(int maxThreadNum) {
        if (maxThreadNum < 1 || maxThreadNum > MAX_THREAD_NUM_PER_OPERATION) {
            throw new IllegalArgumentException("'maxThreadNum' must not less than 1 or exceeded: " + MAX_THREAD_NUM_PER_OPERATION);
        }

        if (this.maxThreadNum == maxThreadNum) {
            return this;
        }

        return new ParallelIteratorIntStream(elements, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public BaseStream.Splitor splitor() {
        return splitor;
    }

    @Override
    public IntStream splitor(BaseStream.Splitor splitor) {
        if (this.splitor == splitor) {
            return this;
        }

        return new ParallelIteratorIntStream(elements, closeHandlers, sorted, maxThreadNum, splitor);
    }

    @Override
    public IntStream onClose(Runnable closeHandler) {
        final Set newCloseHandlers = new AbstractStream.LocalLinkedHashSet<>(N.isNullOrEmpty(this.closeHandlers) ? 1 : this.closeHandlers.size() + 1);

        if (N.notNullOrEmpty(this.closeHandlers)) {
            newCloseHandlers.addAll(this.closeHandlers);
        }

        newCloseHandlers.add(closeHandler);

        return new ParallelIteratorIntStream(elements, newCloseHandlers, sorted, maxThreadNum, splitor);
    }
}