/**
 * Copyright (C) FuseSource, Inc.
 * http://fusesource.com
 *
 * 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.fusesource.fabric.fab;

import java.util.Enumeration;
import java.util.NoSuchElementException;

public class CompoundEnumeration<T> implements Enumeration<T>
{
    private Enumeration<T>[] enums = null;
    private int index = 0;

    public CompoundEnumeration(Enumeration<T>[] enums)
    {
        this.enums = enums;
    }

    public boolean hasMoreElements()
    {
        // if the current enum is null that means this enum is finished
        if (currentEnumeration() == null)
        {
            // No next enum
            return false;
        }
        // If the current enum has more elements, lets go
        return currentEnumeration().hasMoreElements();
    }

    private Enumeration<T> findNextEnumeration(boolean moveCursor)
    {
        return findNextEnumeration(index, moveCursor);
    }

    private Enumeration<T> findNextEnumeration(int cursor, boolean moveCursor)
    {
        // next place in the array
        int next = cursor + 1;
        // If the cursor is still in the array
        if (next < enums.length)
        {

            // If there is something in that place
            // AND the enum is not empty
            if (enums[next] != null &&
                enums[next].hasMoreElements())
            {
                // OK
                if (moveCursor)
                {
                    index = next;
                }
                return enums[next];
            }
            // Try next element
            return findNextEnumeration(next, moveCursor);
        }
        // No more elements available
        return null;
    }

    public T nextElement()
    {
        // ask for the next element of the current enum.
        if (currentEnumeration() != null)
        {
            return currentEnumeration().nextElement();
        }

        // no more elements in this Enum
        // We must throw a NoSuchElementException
        throw new NoSuchElementException("No more elements");
    }

    private Enumeration<T> currentEnumeration()
    {
        if (enums != null)
        {
            if (index < enums.length)
            {
                Enumeration e = enums[index];
                if (e == null || !e.hasMoreElements())
                {
                    // the current enum is null or empty
                    // we probably want to switch to the next one
                    e = findNextEnumeration(true);
                }
                return e;
            }
        }
        return null;
    }
}