feat(v2): 多币种 product(ProductPrice 分币价目 + v1 元回退)+ 结算币种由渠道能力驱动

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nMthbVEmQquxBRKb9Fj8u

internal/gateway/product.go

@@ -9,33 +9,38 @@ import (
 	"github.com/wangjia/pay/internal/money"
 )
 
-// DBProductResolver resolves a SKU (product biz_code) against the products table.
-// v1 Product.Price is a "元" string; we parse it into int64 minor units for the
-// given settlement currency. 加币种维度到 product 是 P3+ 的事;P2 用单一默认币种。
-type DBProductResolver struct {
-	db       *gorm.DB
-	currency string
-}
+// DBProductResolver 按 biz_code 解析套餐,金额取给定结算币种的权威价。
+// 优先查 ProductPrice(分币种 int64 价);该币种无行且币种=CNY 时回退 Product.Price(v1 元 string)。
+type DBProductResolver struct{ db *gorm.DB }
 
-func NewDBProductResolver(db *gorm.DB, currency string) *DBProductResolver {
-	if currency == "" {
-		currency = "CNY"
-	}
-	return &DBProductResolver{db: db, currency: currency}
-}
+func NewDBProductResolver(db *gorm.DB) *DBProductResolver { return &DBProductResolver{db: db} }
 
-func (r *DBProductResolver) Resolve(sku string) (int64, string, string, string, error) {
+func (r *DBProductResolver) Resolve(sku, currency string) (int64, string, string, error) {
 	var p model.Product
 	err := r.db.Where("biz_code = ? AND active = ?", sku, true).First(&p).Error
 	if errors.Is(err, gorm.ErrRecordNotFound) {
-		return 0, "", "", "", ErrProductNotFound
+		return 0, "", "", ErrProductNotFound
 	}
 	if err != nil {
-		return 0, "", "", "", err
+		return 0, "", "", err
 	}
-	minor, err := money.Parse(p.Price, r.currency)
-	if err != nil {
-		return 0, "", "", "", err
+	// 1) 分币种权威价
+	var pp model.ProductPrice
+	err = r.db.Where("product_id = ? AND currency = ?", p.ID, currency).First(&pp).Error
+	if err == nil {
+		return pp.AmountMinor, p.Name, p.BizCode, nil
 	}
-	return minor, r.currency, p.Name, p.BizCode, nil
+	if !errors.Is(err, gorm.ErrRecordNotFound) {
+		return 0, "", "", err
+	}
+	// 2) 回退:仅 CNY 用 v1 Product.Price(元 string)
+	if currency == "CNY" && p.Price != "" {
+		minor, perr := money.Parse(p.Price, "CNY")
+		if perr != nil {
+			return 0, "", "", perr
+		}
+		return minor, p.Name, p.BizCode, nil
+	}
+	// 该套餐不支持此结算币种
+	return 0, "", "", ErrProductNotFound
 }