function first_order_add_fee() {
	global $wpdb, $woocommerce;
	if ( is_user_logged_in() ) {
		$customer_id = get_current_user_id();
		$orderNumCheck = wc_get_customer_order_count( $customer_id ); // count orders by current customer
		$options = get_option( 'first_order_add_settings' );
		$discountType = $options['first_order_choose'];
		$discountValue = $options['first_order_add_value'];
		$subtotal = WC()->cart->cart_contents_total;
		$discount = $discountValue/100;
	    
		$check5order = $orderNumCheck + 1;
		
		if ($check5order % 5 == 0) {
		
			    $product_id = 1802;
				$found = false;
				//check if product already in cart
				if ( sizeof( WC()->cart->get_cart() ) > 0 ) {
					foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {
						$_product = $values['data'];
						if ( $_product->id == $product_id )
							$found = true;
					}
					// if product not found, add it
					if ( ! $found )
						WC()->cart->add_to_cart( $product_id );
				} else {
					// if no products in cart, add it
					WC()->cart->add_to_cart( $product_id );
				}
		}
		
		WC()->cart->add_fee( 'Скидка 10%', -$subtotal*$discount );
		
	}
}

function add_custom_price( $cart_object ) {
    foreach ( $cart_object->cart_contents as $key => $value ) {
		if ($value["product_id"] == "1802") {
			$currPrice = $value['data']->price;
			$currQuant = $value["quantity"];
			$totalPrice = $currPrice * $currQuant;
			$salePrice = $totalPrice - $currPrice;
			$salingPrice = $salePrice/$currQuant;
			$value['data']->price = $salingPrice;
		}
    }
}

add_action( 'woocommerce_before_calculate_totals', 'add_custom_price' );
add_action( 'woocommerce_cart_calculate_fees','first_order_add_fee' );