feat(orders): Add WooCommerce-native calculation endpoints
## Problem:
1. No shipping service options (UPS Ground, UPS Express, etc.)
2. Tax not calculated (11% PPN not showing)
3. Manual cost calculation instead of using WooCommerce core
## Root Cause:
Current implementation manually sets shipping costs from static config:
```php
$shipping_cost = $method->get_option( 'cost', 0 );
$ship_item->set_total( $shipping_cost );
```
This doesn't work for:
- Live rate methods (UPS, FedEx) - need dynamic calculation
- Tax calculation - WooCommerce needs proper context
- Service-level rates (UPS Ground vs Express)
## Solution: Use WooCommerce Native Calculation
### New Endpoints:
1. **POST /woonoow/v1/shipping/calculate**
- Calculates real-time shipping rates
- Uses WooCommerce cart + customer address
- Returns all available methods with costs
- Supports live rate plugins (UPS, FedEx)
- Returns service-level options
2. **POST /woonoow/v1/orders/preview**
- Previews order totals before creation
- Calculates: subtotal, shipping, tax, discounts, total
- Uses WooCommerce cart engine
- Respects tax settings and rates
- Applies coupons correctly
### How It Works:
```php
// Temporarily use WooCommerce cart
WC()->cart->empty_cart();
WC()->cart->add_to_cart( $product_id, $qty );
WC()->customer->set_shipping_address( $address );
WC()->cart->calculate_shipping();
WC()->cart->calculate_totals();
// Get calculated rates
$packages = WC()->shipping()->get_packages();
foreach ( $packages as $package ) {
$rates = $package['rates']; // UPS Ground, UPS Express, etc.
}
// Get totals with tax
$total = WC()->cart->get_total();
$tax = WC()->cart->get_total_tax();
```
### Benefits:
- ✅ Live shipping rates work
- ✅ Service-level options appear
- ✅ Tax calculated correctly
- ✅ Coupons applied properly
- ✅ Uses WooCommerce core logic
- ✅ No reinventing the wheel
### Next Steps (Frontend):
1. Call `/shipping/calculate` when address changes
2. Show service options in dropdown
3. Call `/orders/preview` to show totals with tax
4. Update UI to display tax breakdown
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