/*******************************************************************************
 * Copyright (c) 2005, 2009 Andrea Bittau, University College London, and others
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     Andrea Bittau - initial API and implementation from the PsychoPath XPath 2.0 
 *     Jesper Steen Moller - bug 281938 - handle missing focus
 *******************************************************************************/

package org.eclipse.wst.xml.xpath2.processor.internal;

import org.eclipse.wst.xml.xpath2.api.ResultSequence;
import org.eclipse.wst.xml.xpath2.processor.internal.types.AnyType;

/**
 * set the focus from a result sequence
 */
public class Focus {
	private int _cp; // context position
	private org.eclipse.wst.xml.xpath2.api.ResultSequence _rs; // all items in context

	/**
	 * Sets the _rs to rs and context position to 1.
	 * 
	 * @param rs
	 *            is a ResultSequence and is set to _rs.
	 */
	public Focus(ResultSequence rs) {
		_rs = rs;
		_cp = 1;
	}

	/**
	 * Retrieves previous item from current context position.
	 * 
	 * @return the item from _rs, or null if there is no context item.
	 */
	public AnyType context_item() {
		// idexes start at 0
		if (_cp > _rs.size()) return null;
		return (AnyType)_rs.item(_cp - 1);
	}

	/**
	 * Checks to see if possible to advance rs.
	 * 
	 * @return the boolean.
	 */
	public boolean advance_cp() {
		int size;

		// check if we can advance
		size = _rs.size();
		if (_cp == size)
			return false;

		_cp++;
		return true;
	}

	/**
	 * returns an integer of the current position.
	 * 
	 * @return the current position of rs.
	 */
	public int position() {
		return _cp;
	}

	/**
	 * returns the position of the last item in rs.
	 * 
	 * @return the size of rs.
	 */
	public int last() {
		return _rs.size();
	}

	/**
	 * sets the position.
	 * 
	 * @param p
	 *            is the position that is set.
	 */
	public void set_position(int p) {
		_cp = p; // XXX no checks
	}
}