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

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 * 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

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 *

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package java.util.stream;

import java.util.Optional;

import java.util.OptionalDouble;

import java.util.OptionalInt;

import java.util.OptionalLong;

import java.util.Spliterator;

import java.util.concurrent.CountedCompleter;

import java.util.function.Predicate;

import java.util.function.Supplier;

/**

 * Factory for instances of a short-circuiting {@code TerminalOp} that searches

 * for an element in a stream pipeline, and terminates when it finds one.

 * Supported variants include find-first (find the first element in the

 * encounter order) and find-any (find any element, may not be the first in

 * encounter order.)

 *

 * @since 1.8

 */

final class FindOps {

    private FindOps() { }

    /**

     * Constructs a {@code TerminalOp} for streams of objects.

     *

     * @param <T> the type of elements of the stream

     * @param mustFindFirst whether the {@code TerminalOp} must produce the

     *        first element in the encounter order

     * @return a {@code TerminalOp} implementing the find operation

     */

    public static <T> TerminalOp<T, Optional<T>> makeRef(boolean mustFindFirst) {

        return new FindOp<>(mustFindFirst, StreamShape.REFERENCE, Optional.empty(),

                            Optional::isPresent, FindSink.OfRef::new);

    }

    /**

     * Constructs a {@code TerminalOp} for streams of ints.

     *

     * @param mustFindFirst whether the {@code TerminalOp} must produce the

     *        first element in the encounter order

     * @return a {@code TerminalOp} implementing the find operation

     */

    public static TerminalOp<Integer, OptionalInt> makeInt(boolean mustFindFirst) {

        return new FindOp<>(mustFindFirst, StreamShape.INT_VALUE, OptionalInt.empty(),

                            OptionalInt::isPresent, FindSink.OfInt::new);

    }

    /**

     * Constructs a {@code TerminalOp} for streams of longs.

     *

     * @param mustFindFirst whether the {@code TerminalOp} must produce the

     *        first element in the encounter order

     * @return a {@code TerminalOp} implementing the find operation

     */

    public static TerminalOp<Long, OptionalLong> makeLong(boolean mustFindFirst) {

        return new FindOp<>(mustFindFirst, StreamShape.LONG_VALUE, OptionalLong.empty(),

                            OptionalLong::isPresent, FindSink.OfLong::new);

    }

    /**

     * Constructs a {@code FindOp} for streams of doubles.

     *

     * @param mustFindFirst whether the {@code TerminalOp} must produce the

     *        first element in the encounter order

     * @return a {@code TerminalOp} implementing the find operation

     */

    public static TerminalOp<Double, OptionalDouble> makeDouble(boolean mustFindFirst) {

        return new FindOp<>(mustFindFirst, StreamShape.DOUBLE_VALUE, OptionalDouble.empty(),

                            OptionalDouble::isPresent, FindSink.OfDouble::new);

    }

    /**

     * A short-circuiting {@code TerminalOp} that searches for an element in a

     * stream pipeline, and terminates when it finds one.  Implements both

     * find-first (find the first element in the encounter order) and find-any

     * (find any element, may not be the first in encounter order.)

     *

     * @param <T> the output type of the stream pipeline

     * @param <O> the result type of the find operation, typically an optional

     *        type

     */

    private static final class FindOp<T, O> implements TerminalOp<T, O> {

        private final StreamShape shape;

        final boolean mustFindFirst;

        final O emptyValue;

        final Predicate<O> presentPredicate;

        final Supplier<TerminalSink<T, O>> sinkSupplier;

        /**

         * Constructs a {@code FindOp}.

         *

         * @param mustFindFirst if true, must find the first element in

         *        encounter order, otherwise can find any element

         * @param shape stream shape of elements to search

         * @param emptyValue result value corresponding to "found nothing"

         * @param presentPredicate {@code Predicate} on result value

         *        corresponding to "found something"

         * @param sinkSupplier supplier for a {@code TerminalSink} implementing

         *        the matching functionality

         */

        FindOp(boolean mustFindFirst,

                       StreamShape shape,

                       O emptyValue,

                       Predicate<O> presentPredicate,

                       Supplier<TerminalSink<T, O>> sinkSupplier) {

            this.mustFindFirst = mustFindFirst;

            this.shape = shape;

            this.emptyValue = emptyValue;

            this.presentPredicate = presentPredicate;

            this.sinkSupplier = sinkSupplier;

        }

        @Override

        public int getOpFlags() {

            return StreamOpFlag.IS_SHORT_CIRCUIT | (mustFindFirst ? 0 : StreamOpFlag.NOT_ORDERED);

        }

        @Override

        public StreamShape inputShape() {

            return shape;

        }

        @Override

        public <S> O evaluateSequential(PipelineHelper<T> helper,

                                        Spliterator<S> spliterator) {

            O result = helper.wrapAndCopyInto(sinkSupplier.get(), spliterator).get();

            return result != null ? result : emptyValue;

        }

        @Override

        public <P_IN> O evaluateParallel(PipelineHelper<T> helper,

                                         Spliterator<P_IN> spliterator) {

            return new FindTask<>(this, helper, spliterator).invoke();

        }

    }

    /**

     * Implementation of @{code TerminalSink} that implements the find

     * functionality, requesting cancellation when something has been found

     *

     * @param <T> The type of input element

     * @param <O> The result type, typically an optional type

     */

    private static abstract class FindSink<T, O> implements TerminalSink<T, O> {

        boolean hasValue;

        T value;

        FindSink() {} // Avoid creation of special accessor

        @Override

        public void accept(T value) {

            if (!hasValue) {

                hasValue = true;

                this.value = value;

            }

        }

        @Override

        public boolean cancellationRequested() {

            return hasValue;

        }

        /** Specialization of {@code FindSink} for reference streams */

        static final class OfRef<T> extends FindSink<T, Optional<T>> {

            @Override

            public Optional<T> get() {

                return hasValue ? Optional.of(value) : null;

            }

        }

        /** Specialization of {@code FindSink} for int streams */

        static final class OfInt extends FindSink<Integer, OptionalInt>

                implements Sink.OfInt {

            @Override

            public void accept(int value) {

                // Boxing is OK here, since few values will actually flow into the sink

                accept((Integer) value);

            }

            @Override

            public OptionalInt get() {

                return hasValue ? OptionalInt.of(value) : null;

            }

        }

        /** Specialization of {@code FindSink} for long streams */

        static final class OfLong extends FindSink<Long, OptionalLong>

                implements Sink.OfLong {

            @Override

            public void accept(long value) {

                // Boxing is OK here, since few values will actually flow into the sink

                accept((Long) value);

            }

            @Override

            public OptionalLong get() {

                return hasValue ? OptionalLong.of(value) : null;

            }

        }

        /** Specialization of {@code FindSink} for double streams */

        static final class OfDouble extends FindSink<Double, OptionalDouble>

                implements Sink.OfDouble {

            @Override

            public void accept(double value) {

                // Boxing is OK here, since few values will actually flow into the sink

                accept((Double) value);

            }

            @Override

            public OptionalDouble get() {

                return hasValue ? OptionalDouble.of(value) : null;

            }

        }

    }

    /**

     * {@code ForkJoinTask} implementing parallel short-circuiting search

     * @param <P_IN> Input element type to the stream pipeline

     * @param <P_OUT> Output element type from the stream pipeline

     * @param <O> Result type from the find operation

     */

    @SuppressWarnings("serial")

    private static final class FindTask<P_IN, P_OUT, O>

            extends AbstractShortCircuitTask<P_IN, P_OUT, O, FindTask<P_IN, P_OUT, O>> {

        private final FindOp<P_OUT, O> op;

        FindTask(FindOp<P_OUT, O> op,

                 PipelineHelper<P_OUT> helper,

                 Spliterator<P_IN> spliterator) {

            super(helper, spliterator);

            this.op = op;

        }

        FindTask(FindTask<P_IN, P_OUT, O> parent, Spliterator<P_IN> spliterator) {

            super(parent, spliterator);

            this.op = parent.op;

        }

        @Override

        protected FindTask<P_IN, P_OUT, O> makeChild(Spliterator<P_IN> spliterator) {

            return new FindTask<>(this, spliterator);

        }

        @Override

        protected O getEmptyResult() {

            return op.emptyValue;

        }

        private void foundResult(O answer) {

            if (isLeftmostNode())

                shortCircuit(answer);

            else

                cancelLaterNodes();

        }

        @Override

        protected O doLeaf() {

            O result = helper.wrapAndCopyInto(op.sinkSupplier.get(), spliterator).get();

            if (!op.mustFindFirst) {

                if (result != null)

                    shortCircuit(result);

                return null;

            }

            else {

                if (result != null) {

                    foundResult(result);

                    return result;

                }

                else

                    return null;

            }

        }

        @Override

        public void onCompletion(CountedCompleter<?> caller) {

            if (op.mustFindFirst) {

                    for (FindTask<P_IN, P_OUT, O> child = leftChild, p = null; child != p;

                         p = child, child = rightChild) {

                    O result = child.getLocalResult();

                    if (result != null && op.presentPredicate.test(result)) {

                        setLocalResult(result);

                        foundResult(result);

                        break;

                    }

                }

            }

            super.onCompletion(caller);

        }

    }

}