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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2023 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.s9api;

import net.sf.saxon.om.Item;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.s9api.streams.XdmStream;
import net.sf.saxon.trans.UncheckedXPathException;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.AxisIterator;
import net.sf.saxon.tree.iter.LookaheadIterator;
import net.sf.saxon.tree.iter.LookaheadIteratorImpl;
import net.sf.saxon.tree.iter.SingletonIterator;

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

/**
 * An iterator over an XPath sequence.
 * This class implements the standard Java Iterator interface.
 * Because the Iterator interface does not define any checked
 * exceptions, the hasNext() method of this iterator throws an unchecked
 * exception if a dynamic error occurs while evaluating the expression. Applications
 * wishing to control error handling should take care to catch this exception.
 */
public class XdmSequenceIterator implements Iterator {
    private final LookaheadIterator base;
    private boolean closed = false;

    protected XdmSequenceIterator(SequenceIterator base) {
        try {
            this.base = LookaheadIteratorImpl.makeLookaheadIterator(base);
        } catch (UncheckedXPathException uxe) {
            throw new SaxonApiUncheckedException(uxe.getXPathException());
        } catch (XPathException xe) {
            throw new SaxonApiUncheckedException(xe);
        }
    }

    public static XdmSequenceIterator ofNodes(AxisIterator base) {
        return new XdmSequenceIterator<>(base);
    }

    public static XdmSequenceIterator ofAtomicValues(SequenceIterator base) {
        return new XdmSequenceIterator<>(base);
    }

    protected static XdmSequenceIterator ofNode(XdmNode node) {
        return new XdmSequenceIterator<>(SingletonIterator.makeIterator(node.getUnderlyingNode()));
    }

    /**
     * Returns true if the iteration has more elements. (In other
     * words, returns true if next would return an element
     * rather than throwing an exception.)
     *
     * @return true if the iterator has more elements.
     */
    @Override
    public boolean hasNext() {
        return !closed && base.hasNext();
    }

    /**
     * Returns the next element in the iteration.  Calling this method
     * repeatedly until the {@link #hasNext()} method returns false will
     * return each element in the underlying collection exactly once.
     *
     * @return the next element in the iteration.
     * @throws java.util.NoSuchElementException
     *          iteration has no more elements.
     */
    @Override
    public T next() {
        try {
            Item it = base.next();
            if (it == null) {
                throw new NoSuchElementException();
            } else {
                return (T) XdmItem.wrapItem(it);
            }
        } catch (UncheckedXPathException e) {
            throw new SaxonApiUncheckedException(e.getXPathException());
        }
    }

    /**
     * Not supported on this implementation.
     *
     * @throws UnsupportedOperationException always
     */

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }

    /**
     * The close() method should be called to release resources if the caller wants to stop reading
     * data before reaching the end. This is particularly relevant if the query uses saxon:stream()
     * to read its input, since there will then be another thread supplying data, which will be left
     * in suspended animation if no-one is consuming the data.
     * @since 9.5.1.5 (see bug 2016)
     */

    public void close() {
        closed = true;
        base.close();
    }

    /**
     * Convert this iterator to a Stream
     *
     * @return a Stream delivering the same items as this iterator
     * @since 9.9
     */
    public XdmStream stream() {
        Stream base = StreamSupport.stream(Spliterators.spliteratorUnknownSize(
                this, Spliterator.ORDERED), false);
        base = base.onClose(XdmSequenceIterator.this::close);
        return new XdmStream<>(base);
    }

}