prevent two recurring paymeny items from being added to EDD cart

gistfile1.php

<?php

function check_for_only_one_subscription_purchase_at_a_time( $item ) {

	$cart_items = edd_get_cart_contents();
	
	if ( $cart_items ) {	
		$a = array_values( $item );		
		foreach ( $a as $k => $v ) {			
			if ( is_array( $v ) ) {				
				if ( in_array( "recurring", array_keys( $v ) ) ) {					
					$item_is_recurring_product = TRUE;
				}
			}
		}
		
		foreach ( $cart_items as $key => $value ) {
			$a = array_values( $value );
			foreach ( $a as $k => $v ) {
				if ( is_array( $v ) ) {
					if ( in_array( "recurring", array_keys( $v ) ) ) {
						$recurring_product_in_cart = TRUE;
					}
				}
			}
		}
	}
	
	if ( $item_is_recurring_product || $recurring_product_in_cart ) {
		wp_die( __( 'Sorry, you cannot purchase a subscription with another item in the same checkout session.', 'edd' ) );
	}
	
	return $item;
}
add_filter( 'edd_add_to_cart_item', 'check_for_only_one_subscription_purchase_at_a_time' );