Shipping System

Architecture

Checkout Service
    ↓
Shipping Provider Factory
    ├── Weight-Based Provider
    ├── Manual Provider
    ├── DHL Provider
    ├── FedEx Provider
    └── UPS Provider
    ↓
Shipping Rates → Client selects → Order finalized

Provider trait

#[async_trait]
pub trait ShippingProvider: Send + Sync {
    fn id(&self) -> &str;
    fn name(&self) -> &str;
    fn is_available(&self) -> bool;
    async fn get_rates(&self, from: &Address, to: &Address, package: &Package, options: &RateOptions) -> Result<Vec<ShippingRate>>;
    // ...
}

Weight-based provider

Default provider. Calculates rates based on:

• Total cart weight (from product weights)
• Destination country
• Zone-based rates per 0.5kg

Weight rounds up to nearest 0.5kg.

Zone rates

Zone	Rate/0.5kg
US	$5 (base $5)
EU	$4.50 + VAT
CN	Free
HK/TW/MO/SG	$2.50
Default	$5

Full zone table in Shipping guide.

EU VAT

For EU destinations, VAT is calculated on underdeclared values:

• Wheels: $10/item → $2 VAT
• Bushings: $2/item → $0.40 VAT
• Rate: 20%

Package weight

Product weights are fetched from the database. Products without weight default to 0.5kg.

let weights = cart_service.get_product_weights(&product_ids).await?;
let total_weight: Decimal = items.iter()
    .map(|item| {
        let w = weights.get(&item.product_id).copied().unwrap_or(dec!(0.5));
        Decimal::from(item.quantity) * w
    })
    .sum();

Factory clone

The ShippingProviderFactory must be cloned for the rate aggregator. Each provider is re-created in the clone (providers are stateless).