/*

 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.util.stream;

import java.util.Comparator;

import java.util.Iterator;

import java.util.Objects;

import java.util.Spliterator;

import java.util.Spliterators;

import java.util.function.BiFunction;

import java.util.function.Consumer;

import java.util.function.DoubleConsumer;

import java.util.function.IntConsumer;

import java.util.function.LongConsumer;

/**

 * Utility methods for operating on and creating streams.

 *

 * <p>Unless otherwise stated, streams are created as sequential streams.  A

 * sequential stream can be transformed into a parallel stream by calling the

 * {@code parallel()} method on the created stream.

 *

 * @since 1.8

 */

class Streams {

    private Streams() {

        throw new Error("no instances");

    }

    /**

     * An object instance representing no value, that cannot be an actual

     * data element of a stream.  Used when processing streams that can contain

     * {@code null} elements to distinguish between a {@code null} value and no

     * value.

     */

    static final Object NONE = new Object();

    /**

     * An {@code int} range spliterator.

     */

    static final class RangeIntSpliterator implements Spliterator.OfInt {

        private int from;

        private final int upTo;

        private final int step;

        RangeIntSpliterator(int from, int upTo, int step) {

            this.from = from;

            this.upTo = upTo;

            this.step = step;

        }

        @Override

        public boolean tryAdvance(IntConsumer consumer) {

            boolean hasNext = from < upTo;

            if (hasNext) {

                consumer.accept(from);

                from += step;

            }

            return hasNext;

        }

        @Override

        public void forEachRemaining(IntConsumer consumer) {

            int hUpTo = upTo;

            int hStep = step; // hoist accesses and checks from loop

            for (int i = from; i < hUpTo; i += hStep)

                consumer.accept(i);

            from = upTo;

        }

        @Override

        public long estimateSize() {

            int d = upTo - from;

            return (d / step) + ((d % step == 0) ? 0 : 1);

        }

        @Override

        public int characteristics() {

            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |

                   Spliterator.IMMUTABLE | Spliterator.NONNULL |

                   Spliterator.DISTINCT | Spliterator.SORTED;

        }

        @Override

        public Comparator<? super Integer> getComparator() {

            return null;

        }

        @Override

        public Spliterator.OfInt trySplit() {

            return estimateSize() <= 1

                   ? null

                   : new RangeIntSpliterator(from, from = from + midPoint(), step);

        }

        private int midPoint() {

            // Size is known to be >= 2

            int bisection = (upTo - from) / 2;

            // If bisection > step then round down to nearest multiple of step

            // otherwise round up to step

            return bisection > step ? bisection - bisection % step : step;

        }

    }

    /**

     * A {@code long} range spliterator.

     */

    static final class RangeLongSpliterator implements Spliterator.OfLong {

        private long from;

        private final long upTo;

        private final long step;

        RangeLongSpliterator(long from, long upTo, long step) {

            this.from = from;

            this.upTo = upTo;

            this.step = step;

        }

        @Override

        public boolean tryAdvance(LongConsumer consumer) {

            boolean hasNext = from < upTo;

            if (hasNext) {

                consumer.accept(from);

                from += step;

            }

            return hasNext;

        }

        @Override

        public void forEachRemaining(LongConsumer consumer) {

            long hUpTo = upTo;

            long hStep = step; // hoist accesses and checks from loop

            for (long i = from; i < hUpTo; i += hStep)

                consumer.accept(i);

            from = upTo;

        }

        @Override

        public long estimateSize() {

            long d = upTo - from;

            return (d / step) + ((d % step == 0) ? 0 : 1);

        }

        @Override

        public int characteristics() {

            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |

                   Spliterator.IMMUTABLE | Spliterator.NONNULL |

                   Spliterator.DISTINCT | Spliterator.SORTED;

        }

        @Override

        public Comparator<? super Long> getComparator() {

            return null;

        }

        @Override

        public Spliterator.OfLong trySplit() {

            return estimateSize() <= 1

                   ? null

                   : new RangeLongSpliterator(from, from = from + midPoint(), step);

        }

        private long midPoint() {

            // Size is known to be >= 2

            long bisection = (upTo - from) / 2;

            // If bisection > step then round down to nearest multiple of step

            // otherwise round up to step

            return bisection > step ? bisection - bisection % step : step;

        }

    }

    /**

     * A {@code double} range spliterator.

     *

     * <p>The traversing and splitting logic is equivalent to that of

     * {@code RangeLongSpliterator} for increasing values with a {@code step} of

     * {@code 1}.

     *

     *  <p>A {@code double} value is calculated from the function

     * {@code start + i * step} where {@code i} is the absolute position of the

     * value when traversing an instance of this class that has not been split.

     * This ensures the same values are produced at the same absolute positions

     * regardless of how an instance of this class is split or traversed.

     */

    static final class RangeDoubleSpliterator implements Spliterator.OfDouble {

        private final double from;

        private final double upTo;

        private final double step;

        private long lFrom;

        private final long lUpTo;

        RangeDoubleSpliterator(double from, double upTo, double step, long lFrom, long lUpTo) {

            this.from = from;

            this.upTo = upTo;

            this.step = step;

            this.lFrom = lFrom;

            this.lUpTo = lUpTo;

        }

        @Override

        public boolean tryAdvance(DoubleConsumer consumer) {

            boolean hasNext = lFrom < lUpTo;

            if (hasNext) {

                consumer.accept(from + lFrom * step);

                lFrom++;

            }

            return hasNext;

        }

        @Override

        public void forEachRemaining(DoubleConsumer consumer) {

            double hOrigin = from;

            double hStep = step;

            long hLUpTo = lUpTo;

            long i = lFrom;

            for (; i < hLUpTo; i++) {

                consumer.accept(hOrigin + i * hStep);

            }

            lFrom = i;

        }

        @Override

        public long estimateSize() {

            return lUpTo - lFrom;

        }

        @Override

        public int characteristics() {

            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED |

                   Spliterator.IMMUTABLE | Spliterator.NONNULL |

                   Spliterator.DISTINCT | Spliterator.SORTED;

        }

        @Override

        public Comparator<? super Double> getComparator() {

            return null;

        }

        @Override

        public Spliterator.OfDouble trySplit() {

            return estimateSize() <= 1

                   ? null

                   : new RangeDoubleSpliterator(from, upTo, step, lFrom, lFrom = lFrom + midPoint());

        }

        private long midPoint() {

            // Size is known to be >= 2

            return (lUpTo - lFrom) / 2;

        }

    }

    private static abstract class AbstractStreamBuilderImpl<T, S extends Spliterator<T>> implements Spliterator<T> {

        // >= 0 when building, < 0 when built

        // -1 == no elements

        // -2 == one element, held by first

        // -3 == two or more elements, held by buffer

        int count;

        // Spliterator implementation for 0 or 1 element

        // count == -1 for no elements

        // count == -2 for one element held by first

        @Override

        public S trySplit() {

            return null;

        }

        @Override

        public long estimateSize() {

            return -count - 1;

        }

        @Override

        public int characteristics() {

            return Spliterator.SIZED | Spliterator.SUBSIZED |

                   Spliterator.ORDERED | Spliterator.IMMUTABLE;

        }

    }

    static final class StreamBuilderImpl<T>

            extends AbstractStreamBuilderImpl<T, Spliterator<T>>

            implements StreamBuilder<T> {

        // The first element in the stream

        // valid if count == 1

        T first;

        // The first and subsequent elements in the stream

        // non-null if count == 2

        SpinedBuffer<T> buffer;

        /**

         * Constructor for building a stream of 0 or more elements.

         */

        StreamBuilderImpl() { }

        /**

         * Constructor for a singleton stream.

         *

         * @param t the single element

         */

        StreamBuilderImpl(T t) {

            first = t;

            count = -2;

        }

        // StreamBuilder implementation

        @Override

        public void accept(T t) {

            if (count == 0) {

                first = t;

                count++;

            }

            else if (count > 0) {

                if (buffer == null) {

                    buffer = new SpinedBuffer<>();

                    buffer.accept(first);

                    count++;

                }

                buffer.accept(t);

            }

            else {

                throw new IllegalStateException();

            }

        }

        public StreamBuilder<T> add(T t) {

            accept(t);

            return this;

        }

        @Override

        public Stream<T> build() {

            int c = count;

            if (c >= 0) {

                // Switch count to negative value signalling the builder is built

                count = -count - 1;

                // Use this spliterator if 0 or 1 elements, otherwise use

                // the spliterator of the spined buffer

                return (c < 2) ? StreamSupport.stream(this) : StreamSupport.stream(buffer.spliterator());

            }

            throw new IllegalStateException();

        }

        // Spliterator implementation for 0 or 1 element

        // count == -1 for no elements

        // count == -2 for one element held by first

        @Override

        public boolean tryAdvance(Consumer<? super T> action) {

            if (count == -2) {

                action.accept(first);

                count = -1;

                return true;

            }

            else {

                return false;

            }

        }

        @Override

        public void forEachRemaining(Consumer<? super T> action) {

            if (count == -2) {

                action.accept(first);

                count = -1;

            }

        }

    }

    static final class IntStreamBuilderImpl

            extends AbstractStreamBuilderImpl<Integer, Spliterator.OfInt>

            implements StreamBuilder.OfInt, Spliterator.OfInt {

        // The first element in the stream

        // valid if count == 1

        int first;

        // The first and subsequent elements in the stream

        // non-null if count == 2

        SpinedBuffer.OfInt buffer;

        /**

         * Constructor for building a stream of 0 or more elements.

         */

        IntStreamBuilderImpl() { }

        /**

         * Constructor for a singleton stream.

         *

         * @param t the single element

         */

        IntStreamBuilderImpl(int t) {

            first = t;

            count = -2;

        }

        // StreamBuilder implementation

        @Override

        public void accept(int t) {

            if (count == 0) {

                first = t;

                count++;

            }

            else if (count > 0) {

                if (buffer == null) {

                    buffer = new SpinedBuffer.OfInt();

                    buffer.accept(first);

                    count++;

                }

                buffer.accept(t);

            }

            else {

                throw new IllegalStateException();

            }

        }

        @Override

        public IntStream build() {

            int c = count;

            if (c >= 0) {

                // Switch count to negative value signalling the builder is built

                count = -count - 1;

                // Use this spliterator if 0 or 1 elements, otherwise use

                // the spliterator of the spined buffer

                return (c < 2) ? StreamSupport.intStream(this) : StreamSupport.intStream(buffer.spliterator());

            }

            throw new IllegalStateException();

        }

        // Spliterator implementation for 0 or 1 element

        // count == -1 for no elements

        // count == -2 for one element held by first

        @Override

        public boolean tryAdvance(IntConsumer action) {

            if (count == -2) {

                action.accept(first);

                count = -1;

                return true;

            }

            else {

                return false;

            }

        }

        @Override

        public void forEachRemaining(IntConsumer action) {

            if (count == -2) {

                action.accept(first);

                count = -1;

            }

        }

    }

    static final class LongStreamBuilderImpl

            extends AbstractStreamBuilderImpl<Long, Spliterator.OfLong>

            implements StreamBuilder.OfLong, Spliterator.OfLong {

        // The first element in the stream

        // valid if count == 1

        long first;

        // The first and subsequent elements in the stream

        // non-null if count == 2

        SpinedBuffer.OfLong buffer;

        /**

         * Constructor for building a stream of 0 or more elements.

         */

        LongStreamBuilderImpl() { }

        /**

         * Constructor for a singleton stream.

         *

         * @param t the single element

         */

        LongStreamBuilderImpl(long t) {

            first = t;

            count = -2;

        }

        // StreamBuilder implementation

        @Override

        public void accept(long t) {

            if (count == 0) {

                first = t;

                count++;

            }

            else if (count > 0) {

                if (buffer == null) {

                    buffer = new SpinedBuffer.OfLong();

                    buffer.accept(first);

                    count++;

                }

                buffer.accept(t);

            }

            else {

                throw new IllegalStateException();

            }

        }