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/*
 * Copyright 2017-2019 Crown Copyright
 *
 * 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 uk.gov.gchq.gaffer.commonutil.stream;

import uk.gov.gchq.gaffer.commonutil.CloseableUtil;
import uk.gov.gchq.gaffer.commonutil.iterable.StreamIterable;
import uk.gov.gchq.gaffer.commonutil.iterable.StreamIterator;

import java.util.Iterator;
import java.util.Spliterators;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * Utility class to help with the usage of the Java 8 Streams API in Gaffer.
 */
public final class Streams {

    /**
     * Convert an {@link java.lang.Iterable} to a {@link java.util.stream.Stream}
     * The stream returned must be closed.
     *
     * @param iterable the input iterable
     * @param       the type of object stored in the iterable
     * @return a stream containing the contents of the iterable
     */
    public static  Stream toStream(final Iterable iterable) {
        if (iterable instanceof StreamIterable) {
            return ((StreamIterable) iterable).getStream();
        }

        return StreamSupport.stream(iterable.spliterator(), false)
                .onClose(() -> CloseableUtil.close(iterable));
    }

    /**
     * Convert an array to a {@link java.util.stream.Stream}.
     *
     * @param array the input array
     * @param    the type of object stored in the array
     * @return a stream containing the contents of the array
     */
    public static  Stream toStream(final T[] array) {
        return StreamSupport.stream(Spliterators.spliterator(array, 0), false);
    }

    /**
     * Convert an {@link java.util.Iterator} to a {@link java.util.stream.Stream}
     * The stream returned must be closed.
     *
     * @param iterator the input iterator
     * @param       the type of object stored in the iterator
     * @return a stream containing the contents of the iterator
     */
    public static  Stream toStream(final Iterator iterator) {
        if (iterator instanceof StreamIterator) {
            return ((StreamIterator) iterator).getStream();
        }

        final Iterable iterable = () -> iterator;
        return StreamSupport.stream(iterable.spliterator(), false)
                .onClose(() -> CloseableUtil.close(iterator));
    }

    /**
     * Convert an {@link java.lang.Iterable} to a {@link java.util.stream.Stream}
     * The stream returned must be closed.
     *
     * @param iterable the input iterable
     * @param       the type of object stored in the iterable
     * @return a stream containing the contents of the iterable
     */
    public static  Stream toParallelStream(final Iterable iterable) {
        if (iterable instanceof StreamIterable) {
            return ((StreamIterable) iterable).getStream().parallel();
        }

        return StreamSupport.stream(iterable.spliterator(), true)
                .onClose(() -> CloseableUtil.close(iterable));
    }

    /**
     * Convert an {@link java.util.Iterator} to a {@link java.util.stream.Stream}
     * The stream returned must be closed.
     *
     * @param iterator the input iterator
     * @param       the type of object stored in the iterator
     * @return a stream containing the contents of the iterator
     */
    public static  Stream toParallelStream(final Iterator iterator) {
        if (iterator instanceof StreamIterator) {
            return ((StreamIterator) iterator).getStream().parallel();
        }

        final Iterable iterable = () -> iterator;
        return StreamSupport.stream(iterable.spliterator(), true)
                .onClose(() -> CloseableUtil.close(iterator));
    }

    /**
     * Convert an array to a {@link java.util.stream.Stream}.
     *
     * @param array the input array
     * @param    the type of object stored in the array
     * @return a stream containing the contents of the array
     */
    public static  Stream toParallelStream(final T[] array) {
        return StreamSupport.stream(Spliterators.spliterator(array, 0), true);
    }

    private Streams() {
        // Private constructor to prevent instantiation
    }
}