Automatic template selector for Wordpress Child/Ancestor Categories

jsp_switch_category_template.php

function jsp_switch_category_template() {
    if (is_category()) {
        $ancestors = get_ancestors(get_query_var('cat'),'category');
        $catname = get_query_var('category_name');
        if ($ancestors) {
            $templatePath = TEMPLATEPATH . '/';
            $prefix = 'category-'; //default page template prefix
            $ext = '.php';
            $appender = '_child';
            $parent_id = $ancestors[0];
            $parent_obj = get_term_by('id', $parent_id, 'category');
            $parent_slug = $parent_obj->slug;

            $category_template = $prefix.$catname.$ext; //default template
            $parent_category_template = $prefix.$parent_slug.$ext; //ancestor template
            $parent_category_child_template = $prefix.$parent_slug.$appender.$ext; //children template

            $template = file_exists($templatePath.$category_template) ? $templatePath.$category_template : file_exists($templatePath.$parent_category_child_template) ? $templatePath.$parent_category_child_template : $templatePath.$parent_category_template;

            if (file_exists($template)) {
                load_template($template);
                exit;
            }
        } else {
            return true;
        }
    }
}
add_action('template_redirect','jsp_switch_category_template');