/***************************************
 * /Minimumbestellung 6 Stk und glatt teilbar durch Vielfache von 6 (Modolo 0)
 ***************************************/

// Set a minimum number of products requirement before checking out
add_action( 'woocommerce_check_cart_items', 'spyr_set_min_num_products' );
function spyr_set_min_num_products() {
    // Only run in the Cart or Checkout pages
    if( is_cart() || is_checkout() ) {
        global $woocommerce;

        // Set the minimum number of products before checking out
        $minimum_num_products = 6;
        // Get the Cart's total number of products
        $cart_num_products = WC()->cart->cart_contents_count;

        // Compare values and add an error is Cart's total number of products
        // happens to be less than the minimum required before checking out.
        // Will display a message along the lines of
        // A Minimum of 20 products is required before checking out. (Cont. below)
        // Current number of items in the cart: 6
        if( $cart_num_products < $minimum_num_products || $cart_num_products % 6 != 0) {
            // Display our error message
            wc_add_notice( sprintf( '<strong>Unsere Mindest-Bestellmenge beträgt %s Flaschen. Wir versenden nur Kistenweise, daher muss die Gesamtmenge durch 6 teilbar sein</strong>'
                . '<br />Aktuelle Artikel im Warenkorb: %s.',
                $minimum_num_products,
                $cart_num_products ),
            'error' );
        }
    }
}