rename attachments based on parent-post-title on upload

After trying to add a function to publish_post and creating a lot of unnecessary files I tried to blemish kaisers function to fit my needs.

function modify_uploaded_file_names( $image ) {
    // Use part of the post or user object to rename the image
    get_currentuserinfo();
    global $post, $current_user;

    // only do this if we got the post id, 
    // otherwise they're probably in the media section 
    // rather than uploading an image from a post
    if ( isset( $_REQUEST['post_id'] ) ) {
        // get the ID
        $post_id  = absint( $_REQUEST['post_id'] );

        // get the post OBJECT
        $post_obj  = get_post( $post_id );

        // get the post slug
        $post_slug = sanitize_title($post_obj->post_title); 

        // get the author
        $author = sanitize_title( get_the_author_meta( 'display_name', $post_obj->post_author ) );

        switch( $image['type'] ) {
            case 'image/jpeg' :
                $suffix = 'jpg';
                break;

            case 'image/png' :
                $suffix = 'png';
                break;

            case 'image/gif' :
                $suffix = 'gif';
                break;
        }

        // if we found a slug
        if ( $post_slug ) 
            $image['name'] = "{$author}-{$post_slug}-{$random_number}.{$suffix}";
    }
    else {
        $image_name    = str_place( ' ', '-', strtolower( $current_user->data->user_nicename ) );
        $image['name'] = $image_name . '-' . $file['name'];
    }

    return $image;
}

// Only one arg, so 4th attr not needed - Priority set to later 20
add_filter( 'wp_handle_upload_prefilter', 'my_modify_uploaded_file_names', 20 );

There are only some small changes

1. replaced $post_obj->post_name with sanitize_title($post_obj->post_title) since post_name only was present in my tests when the post already was saved.
2. deleted the random-numbers, cause wp_handle_upload uses wp_unique_filename() anyway.
3. Added the author-name to the file-name, but that’s just something I need.