/*
 * 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.Spliterator;
import java.util.function.BooleanSupplier;
import java.util.function.Consumer;
import java.util.function.DoubleConsumer;
import java.util.function.IntConsumer;
import java.util.function.LongConsumer;
import java.util.function.Supplier;

/**
 * Spliterator implementations for wrapping and delegating spliterators, used
 * in the implementation of the {@link Stream#spliterator()} method.
 *
 * @since 1.8
 */
class StreamSpliterators {

    /**
     * Abstract wrapping spliterator that binds to the spliterator of a
     * pipeline helper on first operation.
     *
     * <p>This spliterator is not late-binding and will bind to the source
     * spliterator when first operated on.
     *
     * <p>A wrapping spliterator produced from a sequential stream
     * cannot be split if there are stateful operations present.
     */
    private static abstract class AbstractWrappingSpliterator<P_IN, P_OUT,
                                                              T_BUFFER extends AbstractSpinedBuffer>
            implements Spliterator<P_OUT> {

        // @@@ Detect if stateful operations are present or not
        //     If not then can split otherwise cannot

        /** True if this spliterator supports splitting */
        final boolean isParallel;

        final PipelineHelper<P_OUT> ph;

        /**
         * Supplier for the source spliterator.  Client provides either a
         * spliterator or a supplier.
         */
        private Supplier<Spliterator<P_IN>> spliteratorSupplier;

        /**
         * Source spliterator.  Either provided from client or obtained from
         * supplier.
         */
        Spliterator<P_IN> spliterator;

        /**
         * Sink chain for the downstream stages of the pipeline, ultimately
         * leading to the buffer. Used during partial traversal.
         */
        Sink<P_IN> bufferSink;

        /**
         * A function that advances one element of the spliterator, pushing
         * it to bufferSink.  Returns whether any elements were processed.
         * Used during partial traversal.
         */
        BooleanSupplier pusher;

        /** Next element to consume from the buffer, used during partial traversal */
        long nextToConsume;

        /** Buffer into which elements are pushed.  Used during partial traversal. */
        T_BUFFER buffer;

        /**
         * True if full traversal has occurred (with possible cancelation).
         * If doing a partial traversal, there may be still elements in buffer.
         */
        boolean finished;

        /** Construct an AbstractWrappingSpliterator from a
         * {@code Supplier<Spliterator>}. */
        AbstractWrappingSpliterator(PipelineHelper<P_OUT> ph,
                                    Supplier<Spliterator<P_IN>> spliteratorSupplier,
                                    boolean parallel) {
            this.ph = ph;
            this.spliteratorSupplier = spliteratorSupplier;
            this.spliterator = null;
            this.isParallel = parallel;
        }

        /** Construct an AbstractWrappingSpliterator from a
         * {@code Spliterator}. */
        AbstractWrappingSpliterator(PipelineHelper<P_OUT> ph,
                                    Spliterator<P_IN> spliterator,
                                    boolean parallel) {
            this.ph = ph;
            this.spliteratorSupplier = null;
            this.spliterator = spliterator;
            this.isParallel = parallel;
        }

        /** Called before advancing to set up spliterator, if needed */
        final void init() {
            if (spliterator == null) {
                spliterator = spliteratorSupplier.get();
                spliteratorSupplier = null;
            }
        }

        /**
         * Get an element from the source, pushing it into the sink chain,
         * setting up the buffer if needed
         * @return whether there are elements to consume from the buffer
         */
        final boolean doAdvance() {
            if (buffer == null) {
                if (finished)
                    return false;

                init();
                initPartialTraversalState();
                nextToConsume = 0;
                bufferSink.begin(spliterator.getExactSizeIfKnown());
                return fillBuffer();
            }
            else {
                ++nextToConsume;
                boolean hasNext = nextToConsume < buffer.count();
                if (!hasNext) {
                    nextToConsume = 0;
                    buffer.clear();
                    hasNext = fillBuffer();
                }
                return hasNext;
            }
        }

        /**
         * Invokes the shape-specific constructor with the provided arguments
         * and returns the result
         */
        abstract AbstractWrappingSpliterator<P_IN, P_OUT, ?> wrap(Spliterator<P_IN> s);

        /**
         * Initializes buffer, sink chain, and pusher for a shape-specific
         * implementation
         */
        abstract void initPartialTraversalState();

        @Override
        public Spliterator<P_OUT> trySplit() {
            if (isParallel && !finished) {
                init();

                Spliterator<P_IN> split = spliterator.trySplit();
                return (split == null) ? null : wrap(split);
            }
            else
                return null;
        }

        /**
         * If the buffer is empty, push elements into the sink chain until
         * the source is empty or cancellation is requested.
         * @return whether there are elements to consume from the buffer
         */
        private boolean fillBuffer() {
            while (buffer.count() == 0) {
                if (bufferSink.cancellationRequested() || !pusher.getAsBoolean()) {
                    if (finished)
                        return false;
                    else {
                        bufferSink.end(); // might trigger more elements
                        finished = true;
                    }
                }
            }
            return true;
        }

        @Override
        public final long estimateSize() {
            init();
            return StreamOpFlag.SIZED.isKnown(ph.getStreamAndOpFlags())
                   ? spliterator.estimateSize()
                   : Long.MAX_VALUE;
        }

        @Override
        public final long getExactSizeIfKnown() {
            init();
            return StreamOpFlag.SIZED.isKnown(ph.getStreamAndOpFlags())
                   ? spliterator.getExactSizeIfKnown()
                   : -1;
        }

        @Override
        public final int characteristics() {
            init();

            // Get the characteristics from the pipeline
            int c = StreamOpFlag.toCharacteristics(StreamOpFlag.toStreamFlags(ph.getStreamAndOpFlags()));

            // Mask off the size and uniform characteristics and replace with
            // those of the spliterator
            // Note that a non-uniform spliterator can change from something
            // with an exact size to an estimate for a sub-split, for example
            // with HashSet where the size is known at the top level spliterator
            // but for sub-splits only an estimate is known
            if ((c & Spliterator.SIZED) != 0) {
                c &= ~(Spliterator.SIZED | Spliterator.SUBSIZED);
                c |= (spliterator.characteristics() & Spliterator.SIZED & Spliterator.SUBSIZED);
            }

            return c;
        }

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

        @Override
        public final String toString() {
            return String.format("%s[%s]", getClass().getName(), spliterator);
        }
    }

    static final class WrappingSpliterator<P_IN, P_OUT>
            extends AbstractWrappingSpliterator<P_IN, P_OUT, SpinedBuffer<P_OUT>> {

        WrappingSpliterator(PipelineHelper<P_OUT> ph,
                            Supplier<Spliterator<P_IN>> supplier,
                            boolean parallel) {
            super(ph, supplier, parallel);
        }

        WrappingSpliterator(PipelineHelper<P_OUT> ph,
                            Spliterator<P_IN> spliterator,
                            boolean parallel) {
            super(ph, spliterator, parallel);
        }

        @Override
        WrappingSpliterator<P_IN, P_OUT> wrap(Spliterator<P_IN> s) {
            return new WrappingSpliterator<>(ph, s, isParallel);
        }

        @Override
        void initPartialTraversalState() {
            SpinedBuffer<P_OUT> b = new SpinedBuffer<>();
            buffer = b;
            bufferSink = ph.wrapSink(b::accept);
            pusher = () -> spliterator.tryAdvance(bufferSink);
        }

        @Override
        public boolean tryAdvance(Consumer<? super P_OUT> consumer) {
            boolean hasNext = doAdvance();
            if (hasNext)
                consumer.accept(buffer.get(nextToConsume));
            return hasNext;
        }

        @Override
        public void forEachRemaining(Consumer<? super P_OUT> consumer) {
            if (buffer == null && !finished) {
                init();

                ph.wrapAndCopyInto((Sink<P_OUT>) consumer::accept, spliterator);
                finished = true;
            }
            else {
                while (tryAdvance(consumer)) { }
            }
        }
    }

    static final class IntWrappingSpliterator<P_IN>
            extends AbstractWrappingSpliterator<P_IN, Integer, SpinedBuffer.OfInt>
            implements Spliterator.OfInt {

        IntWrappingSpliterator(PipelineHelper<Integer> ph,
                               Supplier<Spliterator<P_IN>> supplier,
                               boolean parallel) {
            super(ph, supplier, parallel);
        }

        IntWrappingSpliterator(PipelineHelper<Integer> ph,
                               Spliterator<P_IN> spliterator,
                               boolean parallel) {
            super(ph, spliterator, parallel);
        }

        @Override
        AbstractWrappingSpliterator<P_IN, Integer, ?> wrap(Spliterator<P_IN> s) {
            return new IntWrappingSpliterator<>(ph, s, isParallel);
        }

        @Override
        void initPartialTraversalState() {
            SpinedBuffer.OfInt b = new SpinedBuffer.OfInt();
            buffer = b;
            bufferSink = ph.wrapSink((Sink.OfInt) b::accept);
            pusher = () -> spliterator.tryAdvance(bufferSink);
        }

        @Override
        public Spliterator.OfInt trySplit() {
            return (Spliterator.OfInt) super.trySplit();
        }

        @Override
        public boolean tryAdvance(IntConsumer consumer) {
            boolean hasNext = doAdvance();
            if (hasNext)
                consumer.accept(buffer.get(nextToConsume));
            return hasNext;
        }

        @Override
        public void forEachRemaining(IntConsumer consumer) {
            if (buffer == null && !finished) {
                init();

                ph.wrapAndCopyInto((Sink.OfInt) consumer::accept, spliterator);
                finished = true;
            }
            else {
                while (tryAdvance(consumer)) { }
            }
        }
    }

    static final class LongWrappingSpliterator<P_IN>
            extends AbstractWrappingSpliterator<P_IN, Long, SpinedBuffer.OfLong>
            implements Spliterator.OfLong {

        LongWrappingSpliterator(PipelineHelper<Long> ph,
                                Supplier<Spliterator<P_IN>> supplier,
                                boolean parallel) {
            super(ph, supplier, parallel);
        }

        LongWrappingSpliterator(PipelineHelper<Long> ph,
                                Spliterator<P_IN> spliterator,
                                boolean parallel) {
            super(ph, spliterator, parallel);
        }

        @Override
        AbstractWrappingSpliterator<P_IN, Long, ?> wrap(Spliterator<P_IN> s) {
            return new LongWrappingSpliterator<>(ph, s, isParallel);
        }

        @Override
        void initPartialTraversalState() {
            SpinedBuffer.OfLong b = new SpinedBuffer.OfLong();
            buffer = b;
            bufferSink = ph.wrapSink((Sink.OfLong) b::accept);
            pusher = () -> spliterator.tryAdvance(bufferSink);
        }

        @Override
        public Spliterator.OfLong trySplit() {
            return (Spliterator.OfLong) super.trySplit();
        }

        @Override
        public boolean tryAdvance(LongConsumer consumer) {
            boolean hasNext = doAdvance();
            if (hasNext)
                consumer.accept(buffer.get(nextToConsume));
            return hasNext;
        }

        @Override
        public void forEachRemaining(LongConsumer consumer) {
            if (buffer == null && !finished) {
                init();

                ph.wrapAndCopyInto((Sink.OfLong) consumer::accept, spliterator);
                finished = true;
            }
            else {
                while (tryAdvance(consumer)) { }
            }
        }
    }

    static final class DoubleWrappingSpliterator<P_IN>
            extends AbstractWrappingSpliterator<P_IN, Double, SpinedBuffer.OfDouble>
            implements Spliterator.OfDouble {

        DoubleWrappingSpliterator(PipelineHelper<Double> ph,
                                  Supplier<Spliterator<P_IN>> supplier,
                                  boolean parallel) {
            super(ph, supplier, parallel);
        }

        DoubleWrappingSpliterator(PipelineHelper<Double> ph,
                                  Spliterator<P_IN> spliterator,
                                  boolean parallel) {
            super(ph, spliterator, parallel);
        }

        @Override
        AbstractWrappingSpliterator<P_IN, Double, ?> wrap(Spliterator<P_IN> s) {
            return new DoubleWrappingSpliterator<>(ph, s, isParallel);
        }

        @Override
        void initPartialTraversalState() {
            SpinedBuffer.OfDouble b = new SpinedBuffer.OfDouble();
            buffer = b;
            bufferSink = ph.wrapSink((Sink.OfDouble) b::accept);
            pusher = () -> spliterator.tryAdvance(bufferSink);
        }

        @Override
        public Spliterator.OfDouble trySplit() {
            return (Spliterator.OfDouble) super.trySplit();
        }

        @Override
        public boolean tryAdvance(DoubleConsumer consumer) {
            boolean hasNext = doAdvance();
            if (hasNext)
                consumer.accept(buffer.get(nextToConsume));
            return hasNext;
        }

        @Override
        public void forEachRemaining(DoubleConsumer consumer) {
            if (buffer == null && !finished) {
                init();

                ph.wrapAndCopyInto((Sink.OfDouble) consumer::accept, spliterator);
                finished = true;
            }
            else {
                while (tryAdvance(consumer)) { }
            }
        }
    }

    /**
     * Spliterator implementation that delegates to an underlying spliterator,
     * acquiring the spliterator from a {@code Supplier<Spliterator>} on the
     * first call to any spliterator method.
     * @param <T>
     */
    static class DelegatingSpliterator<T> implements Spliterator<T> {
        private final Supplier<Spliterator<T>> supplier;

        private Spliterator<T> s;

        @SuppressWarnings("unchecked")
        DelegatingSpliterator(Supplier<? extends Spliterator<T>> supplier) {
            this.supplier = (Supplier<Spliterator<T>>) supplier;
        }

        Spliterator<T> get() {
            if (s == null) {
                s = supplier.get();
            }
            return s;
        }

        @Override
        public Spliterator<T> trySplit() {
            return get().trySplit();
        }

        @Override
        public boolean tryAdvance(Consumer<? super T> consumer) {
            return get().tryAdvance(consumer);
        }

        @Override
        public void forEachRemaining(Consumer<? super T> consumer) {
            get().forEachRemaining(consumer);
        }

        @Override
        public long estimateSize() {
            return get().estimateSize();
        }

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

        @Override
        public Comparator<? super T> getComparator() {
            return get().getComparator();
        }

        @Override
        public long getExactSizeIfKnown() {
            return get().getExactSizeIfKnown();
        }

        @Override
        public String toString() {
            return getClass().getName() + "[" + get() + "]";
        }

        static final class OfInt extends DelegatingSpliterator<Integer> implements Spliterator.OfInt {
            private Spliterator.OfInt s;

            OfInt(Supplier<Spliterator.OfInt> supplier) {
                super(supplier);
            }

            @Override
            Spliterator.OfInt get() {
                if (s == null) {
                    s = (Spliterator.OfInt) super.get();
                }
                return s;
            }

            @Override
            public Spliterator.OfInt trySplit() {
                return get().trySplit();
            }

            @Override
            public boolean tryAdvance(IntConsumer consumer) {
                return get().tryAdvance(consumer);
            }

            @Override
            public void forEachRemaining(IntConsumer consumer) {
                get().forEachRemaining(consumer);
            }
        }

        static final class OfLong extends DelegatingSpliterator<Long> implements Spliterator.OfLong {
            private Spliterator.OfLong s;

            OfLong(Supplier<Spliterator.OfLong> supplier) {
                super(supplier);
            }

            @Override
            Spliterator.OfLong get() {
                if (s == null) {
                    s = (Spliterator.OfLong) super.get();
                }
                return s;
            }

            @Override
            public Spliterator.OfLong trySplit() {
                return get().trySplit();
            }

            @Override
            public boolean tryAdvance(LongConsumer consumer) {
                return get().tryAdvance(consumer);
            }

            @Override
            public void forEachRemaining(LongConsumer consumer) {
                get().forEachRemaining(consumer);
            }
        }

        static final class OfDouble extends DelegatingSpliterator<Double> implements Spliterator.OfDouble {
            private Spliterator.OfDouble s;

            OfDouble(Supplier<Spliterator.OfDouble> supplier) {
                super(supplier);
            }

            @Override
            Spliterator.OfDouble get() {
                if (s == null) {
                    s = (Spliterator.OfDouble) super.get();
                }
                return s;
            }

            @Override
            public Spliterator.OfDouble trySplit() {
                return get().trySplit();
            }

            @Override
            public boolean tryAdvance(DoubleConsumer consumer) {
                return get().tryAdvance(consumer);
            }

            @Override
            public void forEachRemaining(DoubleConsumer consumer) {
                get().forEachRemaining(consumer);
            }
        }
    }
}