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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 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.tree.iter;

import net.sf.saxon.om.NodeInfo;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.pattern.NodeTest;
import net.sf.saxon.trans.XPathException;

/**
 * An iterator over nodes, that prepends a given node to the nodes
 * returned by another iterator. Used to modify an iterator over axis A
 * to one that iterates over A-OR-SELF.
 */

public class PrependIterator implements AxisIterator {

    NodeInfo start;
    AxisIterator base;
    int position = 0;

    public PrependIterator(NodeInfo start, AxisIterator base) {
        this.start = start;
        this.base = base;
    }

    /**
     * Move to the next node, without returning it. Returns true if there is
     * a next node, false if the end of the sequence has been reached. After
     * calling this method, the current node may be retrieved using the
     * current() function.
     */

    public boolean moveNext() {
        return (next() != null);
    }


    /**
     * Get the next item in the sequence. 

     *
     * @return the next Item. If there are no more nodes, return null.
     */

    /*@Nullable*/ public NodeInfo next() {
        if (position == 0) {
            position = 1;
            return start;
        }
        NodeInfo n = base.next();
        if (n == null) {
            position = -1;
        } else {
            position++;
        }
        return n;
    }

    /**
     * Get the current item in the sequence.
     *
     * @return the current item, that is, the item most recently returned by
     *         next()
     */

    /*@Nullable*/ public NodeInfo current() {
        if (position() == 1) {
            return start;
        } else if (position < 1) {
            return null;
        } else {
            return base.current();
        }
    }

    /**
     * Get the current position
     *
     * @return the position of the current item (the item most recently
     *         returned by next()), starting at 1 for the first node
     */

    public int position() {
       return position;
    }

    public void close() {
        base.close();
    }

    /**
     * Return an iterator over an axis, starting at the current node.
     *
     * @param axis the axis to iterate over, using a constant such as
     *             {@link net.sf.saxon.om.AxisInfo#CHILD}
     * @param test a predicate to apply to the nodes before returning them.
     * @throws NullPointerException if there is no current node
     */

    public AxisIterator iterateAxis(byte axis, NodeTest test) {
        return current().iterateAxis(axis, test);
    }

    /**
     * Return the atomized value of the current node.
     *
     * @return the atomized value.
     * @throws NullPointerException if there is no current node
     */

    public Sequence atomize() throws XPathException {
        return current().atomize();
    }

    /**
     * Return the string value of the current node.
     *
     * @return the string value, as an instance of CharSequence.
     * @throws NullPointerException if there is no current node
     */

    public CharSequence getStringValue() {
        return ((NodeInfo)current()).getStringValueCS();
    }

    /**
     * Get another iterator over the same sequence of items, positioned at the
     * start of the sequence
     *
     * @return a new iterator over the same sequence
     */

    /*@NotNull*/ public AxisIterator getAnother() {
        return new PrependIterator(start, base.getAnother());
    }

    /**
     * Get properties of this iterator, as a bit-significant integer.
     *
     * @return the properties of this iterator. This will be some combination of
     *         properties such as {@link #GROUNDED}, {@link #LAST_POSITION_FINDER},
     *         and {@link #LOOKAHEAD}. It is always
     *         acceptable to return the value zero, indicating that there are no known special properties.
     *         It is acceptable for the properties of the iterator to change depending on its state.
     */

    public int getProperties() {
        return 0;
    }


}