/* this is the 'main' method of my "download & unarchive" operation. */
- (void)main
{
	struct archive *archive;
	int result;

    // kick off downloading the archive file from my web site
    [self beginDownload];

    // initialize the libarchive reading structures
    result = [self initArchive:&archive];

    // here's the loop that both signals for progress updates and deals with next entries
    while (result == ARCHIVE_OK && ![self isCancelled])
    {
        [self updateProgressForArchive:archive];
        result = [self processNextArchiveEntry:archive];
    }

    // all good loops must come to an end
    if (result == ARCHIVE_EOF)
    {
        result = archive_read_finish(archive);
    }

    // this is somewhat lame, but we _are_ in an NSOperation so it's polite
    if ([self isCancelled])
    {
        NSLog(@"MyDownloadOperation was canceled");
        [downloadThread cancel];
        [[pipe fileHandleForReading] readDataToEndOfFile];  // Unblock the download thread
        result = ARCHIVE_RETRY;
    }

    // everything worked!
    if (result == ARCHIVE_OK)
    {
        [self moveContentFromStagingAreaToFinalArea]; // this is how my app rolls; yours may be different
    }
    else
    {
        [self removeTempDirectory]; // this is how my app rolls; yours may be different
    }
}


- (void)beginDownload
{
    pipe = [NSPipe new];
    downloadThread = [[MyDownloadThread alloc] initWithURL:myDownloadUrl stream:[pipe fileHandleForWriting]];
    [downloadThread start];
}


- (int)initArchive:(struct archive **)outArchive
{
    struct archive *archive = NULL;
    int result = ARCHIVE_OK;

    archive = archive_read_new();
    archive_read_support_compression_bzip2(archive);
    archive_read_support_compression_gzip(archive);
    archive_read_support_format_tar(archive);
    archive_read_support_format_gnutar(archive);

    result = archive_read_open_fd(archive, [[pipe fileHandleForReading] fileDescriptor], getpagesize());

    if(result == ARCHIVE_OK && outArchive != NULL)
    {
        *outArchive = archive;
    }

    lastArchivePosition = 0;

    return result;
}