/*
 * Copyright 2004,2005 The Apache Software Foundation.
 *
 * 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 org.apache.ws.commons.om.impl.llom.traverse;

import org.apache.ws.commons.om.OMException;
import org.apache.ws.commons.om.OMNode;

import java.util.Iterator;

/**
 * Class OMChildrenIterator
 */
public class OMChildrenIterator implements Iterator {
    /**
     * Field currentChild
     */
    protected OMNode currentChild;

    /**
     * Field lastChild
     */
    protected OMNode lastChild;

    /**
     * Field nextCalled
     */
    protected boolean nextCalled = false;

    /**
     * Field removeCalled
     */
    protected boolean removeCalled = false;

    /**
     * Constructor OMChildrenIterator.
     *
     * @param currentChild
     */
    public OMChildrenIterator(OMNode currentChild) {
        this.currentChild = currentChild;
    }

    /**
     * Removes the last element returned by the iterator (optional operation) 
     * from the underlying collection.   This method must be called only once per
     * call to <tt>next</tt>.  The behavior of an iterator is unspecified if
     * the underlying collection is modified while the iteration is in
     * progress in any way other than by calling this method.
     *
     * @throws UnsupportedOperationException if the <tt>remove</tt>
     *                                       operation is not supported by this Iterator.
     * @throws IllegalStateException         if the <tt>next</tt> method has not
     *                                       yet been called, or the <tt>remove</tt> method has already
     *                                       been called after the last call to the <tt>next</tt>
     *                                       method.
     */
    public void remove() {
        if (!nextCalled) {
            throw new IllegalStateException(
                    "next method has not yet being called");
        }
        if (removeCalled) {
            throw new IllegalStateException("remove has already being called");
        }
        removeCalled = true;

        // since this acts on the last child there is no need to mess with the current child
        if (lastChild == null) {
            throw new OMException("cannot remove a child at this stage!");
        }
        lastChild.detach();
    }

    /**
     * Returns <tt>true</tt> if the iteration has more elements. (In other
     * words, returns <tt>true</tt> if <tt>next</tt> would return an element
     * rather than throwing an exception.)
     *
     * @return Returns <tt>true</tt> if the iterator has more elements.
     */
    public boolean hasNext() {
        return (currentChild != null);
    }

    /**
     * Returns the next element in the iteration.
     *
     * @return Returns the next element in the iteration.
     * @throws java.util.NoSuchElementException
     *          iteration has no more elements.
     */
    public Object next() {
        nextCalled = true;
        removeCalled = false;
        if (hasNext()) {
            lastChild = currentChild;
            currentChild = currentChild.getNextOMSibling();
            return lastChild;
        }
        return null;
    }
}