/*

 * Copyright (c) 1998, 2011, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This source code is provided to illustrate the usage of a given feature

 * or technique and has been deliberately simplified. Additional steps

 * required for a production-quality application, such as security checks,

 * input validation and proper error handling, might not be present in

 * this sample code.

 */

package com.sun.tools.example.debug.tty;

import com.sun.jdi.ThreadGroupReference;

import java.util.List;

import java.util.Stack;

import java.util.ArrayList;

import java.util.Iterator;

/**

 * Descend the tree of thread groups.

 * @author Robert G. Field

 */

class ThreadGroupIterator implements Iterator<ThreadGroupReference> {

    private final Stack<Iterator<ThreadGroupReference>> stack = new Stack<Iterator<ThreadGroupReference>>();

    ThreadGroupIterator(List<ThreadGroupReference> tgl) {

        push(tgl);

    }

    ThreadGroupIterator(ThreadGroupReference tg) {

        List<ThreadGroupReference> tgl = new ArrayList<ThreadGroupReference>();

        tgl.add(tg);

        push(tgl);

    }

    ThreadGroupIterator() {

        this(Env.vm().topLevelThreadGroups());

    }

    private Iterator<ThreadGroupReference> top() {

        return stack.peek();

    }

    /**

     * The invariant in this class is that the top iterator

     * on the stack has more elements.  If the stack is

     * empty, there is no top.  This method assures

     * this invariant.

     */

    private void push(List<ThreadGroupReference> tgl) {

        stack.push(tgl.iterator());

        while (!stack.isEmpty() && !top().hasNext()) {

            stack.pop();

        }

    }

    @Override

    public boolean hasNext() {

        return !stack.isEmpty();

    }

    @Override

    public ThreadGroupReference next() {

        return nextThreadGroup();

    }

    public ThreadGroupReference nextThreadGroup() {

        ThreadGroupReference tg = top().next();

        push(tg.threadGroups());

        return tg;

    }

    @Override

    public void remove() {

        throw new UnsupportedOperationException();

    }

    static ThreadGroupReference find(String name) {

        ThreadGroupIterator tgi = new ThreadGroupIterator();

        while (tgi.hasNext()) {

            ThreadGroupReference tg = tgi.nextThreadGroup();

            if (tg.name().equals(name)) {

                return tg;

            }

        }

        return null;

    }

}