package net.sf.saxon.tree;
import net.sf.saxon.om.AxisIterator;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.LookaheadIterator;
import net.sf.saxon.pattern.NodeTest;
import net.sf.saxon.value.Value;
import net.sf.saxon.trans.XPathException;

abstract class TreeEnumeration implements AxisIterator, LookaheadIterator {

    protected NodeImpl start;
	protected NodeImpl next;
	protected NodeTest nodeTest;
	protected NodeImpl current = null;
	protected int position = 0;
	//protected int last = -1;

	/**
	* Create an axis enumeration for a given type and name of node, from a given
	* origin node
     * @param origin the node from which the axis originates
     * @param nodeTest test to be satisfied by the returned nodes, or null if all nodes
     * are to be returned.
	*/

	public TreeEnumeration(NodeImpl origin, NodeTest nodeTest) {
	    next = origin;
	    start = origin;
	    this.nodeTest = nodeTest;
	}

	/**
	* Test whether a node conforms to the node type and name constraints.
	* Note that this returns true if the supplied node is null, this is a way of
	* terminating a loop.
	*/

	protected boolean conforms(NodeImpl node) {
	    if (node==null || nodeTest==null) {
            return true;
        }
		return nodeTest.matches(node);
	}

	/**
	* Advance along the axis until a node is found that matches the required criteria
	*/

	protected final void advance() {
	    do {
	        step();
	    } while (!conforms(next));
	}

	/**
	* Advance one step along the axis: the resulting node might not meet the required
	* criteria for inclusion
	*/

	protected abstract void step();

    /**
     * Determine whether there are more items to come. Note that this operation
     * is stateless and it is not necessary (or usual) to call it before calling
     * next(). It is used only when there is an explicit need to tell if we
     * are at the last element.
     *
     * @return true if there are more items in the sequence
     */

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

    /**
     * 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);
    }


	/**
	* Return the next node in the enumeration
	*/

	public final Item next() {
        if (next==null) {
            current = null;
            position = -1;
            return null;
        } else {
            current = next;
            position++;
            advance();
            return current;
        }
	}

	/**
	* Return the current Item
	*/

	public final Item current() {
	    return current;
	}

	/**
	* Return the current position
	*/

	public final int position() {
	    return position;
	}

    public void 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.Axis#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 Value 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 current.getStringValueCS();
    }

    /**
     * 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 LOOKAHEAD;
    }

    /**
     * Indicate that any nodes returned in the sequence will be atomized. This
     * means that if it wishes to do so, the implementation can return the typed
     * values of the nodes rather than the nodes themselves. The implementation
     * is free to ignore this hint.
     * @param atomizing true if the caller of this iterator will atomize any
     * nodes that are returned, and is therefore willing to accept the typed
     * value of the nodes instead of the nodes themselves.
     */

    //public void setIsAtomizing(boolean atomizing) {}
}


//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (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.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//
