type Product struct {
    ID    string  `json:"id"`
    Name  string  `json:"name"`
    Price float64 `json:"price"`
}
type CartItem struct {
Product
Quantity int json:"quantity"
}
type Cart struct {
Items map[string]*CartItem json:"items"
}

func (c *Cart) AddItem(p Product, qty int) {
    if item, exists := c.Items[p.ID]; exists {
        item.Quantity += qty
    } else {
        c.Items[p.ID] = &CartItem{Product: p, Quantity: qty}
    }
}
func (c *Cart) RemoveItem(id string) {
delete(c.Items, id)
}
func (c *Cart) UpdateQuantity(id string, qty int) {
if item, exists := c.Items[id]; exists {
if qty <= 0 {
delete(c.Items, id)
} else {
item.Quantity = qty
}
}
}
func (c Cart) Total() float64 {
total := 0.0
for _, item := range c.Items {
total += item.Price  float64(item.Quantity)
}
return total
}

var cart = Cart{Items: make(map[string]*CartItem)}
func addHandler(w http.ResponseWriter, r *http.Request) {
var req struct {
Product  Product json:"product"
Quantity int     json:"quantity"
}
json.NewDecoder(r.Body).Decode(&req)
cart.AddItem(req.Product, req.Quantity)
w.Header().Set("Content-Type", "application/json")
json.NewEncoder(w).Encode(cart)
}
func getHandler(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
json.NewEncoder(w).Encode(cart)
}

func main() {
    http.HandleFunc("/cart/add", addHandler)
    http.HandleFunc("/cart", getHandler)
    http.ListenAndServe(":8080", nil)
}

# 添加商品
curl -X POST http://localhost:8080/cart/add \
  -H "Content-Type: application/json" \
  -d '{"product":{"id":"p1","name":"iPhone","price":6999},"quantity":1}'
获取购物车
curl http://localhost:8080/cart