/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 1997-2017 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://oss.oracle.com/licenses/CDDL+GPL-1.1
 * or LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyright [year] [name of copyright owner]"
 *
 * Contributor(s):
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

package com.sun.xml.bind.v2.util;

import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

/**
 * {@link Iterator} that walks over a map of maps.
 *
 * @author Kohsuke Kawaguchi
 * @since 2.0
 */
public final class FlattenIterator<T> implements Iterator<T> {

    private final Iterator<? extends Map<?,? extends T>> parent;
    private Iterator<? extends T> child = null;
    private T next;

    public FlattenIterator( Iterable<? extends Map<?,? extends T>> core ) {
        this.parent = core.iterator();
    }


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

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

    public T next() {
        T r = next;
        next = null;
        if(r==null)
            throw new NoSuchElementException();
        return r;
    }

    private void getNext() {
        if(next!=null)  return;

        if(child!=null && child.hasNext()) {
            next = child.next();
            return;
        }
        // child is empty
        if(parent.hasNext()) {
            child = parent.next().values().iterator();
            getNext();
        }
        // else
        //      no more object
    }
}
