Question

WooCommerce的Fees API包含三个函数，add_fee(), get_fees()和calculate_fees()。我们可以用add_fee()向订单中添加固定费用或者百分比费用，需要注意的是使用哪个action添加。

回顾代码，发现问题

在之前写的WooCommerce实用代码集合一文中，写过一段添加手续费的代码，用的action是woocommerce_calculate_totals，最近需要加一个可以应用税率的手续费，进而发现代码中有个逻辑错误。

$woocommerce->cart->add_fee( 'Surcharge', $surcharge, false, '' );
$woocommerce->cart->fee_total += $surcharge;

第一句话用Fee API增加了费用，第二句话把这个费用和总费用相加，add_fee第三个参数含义为是否应用税率。

既然add_fee可以给费用增加一个税钱，第二句话中却没有税的踪影，岂不是要出错了！

细看woocommerce的fee api后发现，正确的action是woocommerce_cart_calculate_fees，第二句话并不需要。

下面是正确的代码，这里允许给费用加税。

add_action( 'woocommerce_cart_calculate_fees','woocommerce_custom_surcharge' );
function woocommerce_custom_surcharge() {
    global $woocommerce;
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;
    $percentage = 0.01;
    $surcharge = ( $woocommerce->cart->cart_contents_total + $woocommerce->cart->shipping_total ) * $percentage;
    $woocommerce->cart->add_fee( 'Surcharge', $surcharge,true );
}

WooCommerce Fees API

Fees API位于class-wc-cart.php中

三个函数代码如下，供参考

/*-----------------------------------------------------------------------------------*/
/* Fees API to add additonal costs to orders */
/*-----------------------------------------------------------------------------------*/

        /**
         * add_fee function.
         *
         * @param mixed $name
         * @param mixed $amount
         * @param bool $taxable (default: false)
         * @param string $tax_class (default: '')
         */
        public function add_fee( $name, $amount, $taxable = false, $tax_class = '' ) {
                if ( empty( $this->fees ) )
                        $this->fees = array();

                $new_fee 			= new stdClass();
                $new_fee->id 		= sanitize_title( $name );
                $new_fee->name 		= esc_attr( $name );
                $new_fee->amount	= (float) esc_attr( $amount );
                $new_fee->tax_class	= $tax_class;
                $new_fee->taxable	= $taxable ? true : false;
                $new_fee->tax		= 0;

                $this->fees[] 		= $new_fee;
        }

        /**
         * get_fees function.
         *
         * @access public
         * @return void
         */
        public function get_fees() {
                return array_filter( (array) $this->fees );
        }

        /**
         * Calculate fees
         */
        public function calculate_fees() {

                // Fire an action where developers can add their fees
                do_action( 'woocommerce_cart_calculate_fees', $this );

                // If fees were added, total them and calculate tax
                if ( $fees = $this->get_fees() ) {
                        foreach ( $fees as $fee ) {
                                $this->fee_total += $fee->amount;

                                if ( $fee->taxable ) {
                                        // Get tax rates
                                        $tax_rates = $this->tax->get_rates( $fee->tax_class );
                                        $fee_taxes = $this->tax->calc_tax( $fee->amount, $tax_rates, false );

                                        // Store
                                        $fee->tax  = array_sum( $fee_taxes );

                                        // Tax rows - merge the totals we just got
                                        foreach ( array_keys( $this->taxes + $fee_taxes ) as $key ) {
                                            $this->taxes[ $key ] = ( isset( $fee_taxes[ $key ] ) ? $fee_taxes[ $key ] : 0 ) + ( isset( $this->taxes[ $key ] ) ? $this->taxes[ $key ] : 0 );
                                        }
                                }
                        }
                }
        }