/*
 ** Tim feel free to integrate this code here.
 **
 ** This code has been placed into the Public Domain.
 ** This code was written by David M. Gaskin in 1999.
 **
 */

package com.ice.tar;

import java.io.IOException;
import java.util.Enumeration;
import java.util.NoSuchElementException;

/**
 * Enumerate the contents of a "tar" file.
 *
 * Last updated 26th Mar 1999.
 *
 * @author  David. M. Gaskin.
 * @version Version 1.0 Mar 1999
 * @since    Version 1.0
 */

public class TarEntryEnumerator implements Enumeration
{
    /**
     * The instance on which the enumeration works.
     */
    private TarInputStream tis = null;

    /**
     * Has EndOfFile been reached?
     */
    private boolean eof = false;

    /**
     * The read ahead entry (or <B><I>null</I></B> if no read ahead exists)
     */
    private TarEntry readAhead = null;

    /**
     * Construct an instance given a TarInputStream. This method is package
     * private because it is not initially forseen that an instance of this class
     * should be constructed from outside the package. Should it become necessary
     * to construct an instance of this class from outside the package in which it
     * exists then the constructor should be made <B>protected</B> and an empty
     * subclass should be written in the other package.
     * @param tis the <B>TarInputStream</B> on which this enumeration has
     *  to be based.
     */
    public TarEntryEnumerator(TarInputStream tis)
    {
        this.tis = tis;
        eof = false;
    }

    /**
     * Return the next element in the enumeration. This is a required method
     * for implementing <B>java.util.Enumeration</B>.
     *
     * @return the next Object in the enumeration
     * @exception NoSuchElementException should an attempt be made to
     *  read beyond EOF
     */
    public Object nextElement() throws NoSuchElementException
    {
        if (eof && (readAhead == null))
            throw new NoSuchElementException();

        TarEntry rc = null;
        if (readAhead != null)
        {
            rc = readAhead;
            readAhead = null;
        }
        else
        {
            rc = getNext();
        }

        return rc;
    }

    /**
     * Return <B>true</B> if there are more elements in the enumeration.
     *
     * @return <B>true</B> if there are more elements in the enumeration.
     */
    public boolean hasMoreElements()
    {
        if (eof)
            return false;

        boolean rc = false;
        readAhead = getNext();
        if (readAhead != null)
            rc = true;

        return rc;
    }

    /**
     * Return the next element of <B>null</B> if there is no next element or
     * if an error occured.
     *
     * @return the next element of <B>null</B> if there is no next element or
     * if an error occured.
     */
    private TarEntry getNext()
    {
        TarEntry rc = null;
        try
        {
            rc = tis.getNextEntry();
        }
        catch (IOException ex)
        {
            // null will be returned but should not occur
            ex.printStackTrace();
        }

        if (rc == null)
            eof = true;

        return rc;
    }
}