Custom Coutry query var

//Modify this function only
function countries() {
	   $args = array(
        'post_type' => 'country', //change as needed
        'post_status' => 'publish',
        'posts_per_page' => -1);
		
		$slugs = array();
		
		$countries = new WP_Query( $args );
		
		if ( $countries->have_posts() ) : 
		    while ( $countries->have_posts() ) : $countries->the_post();
		       array_push( $slugs, get_post_field( 'post_name', get_the_ID()) );
		    endwhile;
		endif;

    return $slugs;
}

function prepend_default_rewrite_rules( $rules ) {

    // Prepare for new rules
    $new_rules = [];

    // Set up Country, except default one
    //$country_slugs = ['us', 'bd', 'in', 'uk', 'cn'];
	
	$country_slugs = countries();

    // Generate language slug regex
    $countries_slug = '(?:' . implode( '/|', $country_slugs ) . '/)?';


    // Set up the list of rules that don't need to be prefixed
    $whitelist = [
        '^wp-json/?$',
        '^wp-json/(.*)?',
        '^index.php/wp-json/?$',
        '^index.php/wp-json/(.*)?'
    ];

    // Set up the new rule for home page
    $new_rules['(?:' . implode( '/|', $country_slugs ) . ')/?$'] = 'index.php';

    // Loop through old rules and modify them
    foreach ( $rules as $key => $rule ) {

        // Re-add those whitelisted rules without modification
        if ( in_array( $key, $whitelist ) ) {

            $new_rules[ $key ] = $rule;

        // Update rules starting with ^ symbol
        } elseif ( substr( $key, 0, 1 ) === '^' ) { 

            $new_rules[ $countries_slug . substr( $key, 1 ) ] = $rule;


        // Update other rules
        } else {

            $new_rules[ $countries_slug . $key ] = $rule;

        }
    }


    // Return out new rules
    return $new_rules;
}
add_filter( 'rewrite_rules_array', 'prepend_default_rewrite_rules' );