Custom rewrite for WordPress with custom template

gistfile1.php

<?php

// enables you to use example url "/showcase/case-title" and pushes it to "single-showcases.php" template for rendering

function mu_custom_rewrites() {

	global $wp;

	$wp->add_query_var('case');
	add_rewrite_tag('%case%', '([^/]+)', 'case=');
	add_permastruct('showcase', '/showcase/%case%/', false);
		
}

add_action('init', 'my_custom_rewrites', 10, 0);

function my_parse_query() {

	global $wp_query;

	if (get_query_var('case') != '') {			
		add_action('template_redirect', 'my_template_redirect');
	}

}

add_filter('parse_query','my_parse_query');

function my_template_redirect() {

	global $template;

	if (get_query_var('case') != '') {

		$template = get_query_template('single-showcases');
		include ($template);
		exit();

	}
}