feat(v2): weighted 路由策略(按 Weight,hash(OutTradeNo) 确定性)

internal/accounts/weighted.go

@@ -0,0 +1,48 @@
+package accounts
+
+import (
+	"hash/fnv"
+
+	"github.com/wangjia/pay/config"
+)
+
+// Weighted 按 Weight 加权选账户,决策源为 hash(OutTradeNo)(确定性、可复现、跨节点一致,
+// 见计划 D1)。Weight<=0 记 1(对齐 model.Account gorm default:1)。retry 换号由
+// Router 的 ExcludeAccounts 过滤驱动,不依赖随机。
+type Weighted struct{}
+
+func NewWeighted() *Weighted { return &Weighted{} }
+
+func (Weighted) Pick(_ string, candidates []config.AccountConfig, hint PickHint) (config.AccountConfig, error) {
+	if len(candidates) == 0 {
+		return config.AccountConfig{}, ErrNoAccount
+	}
+	if hint.OutTradeNo == "" {
+		return candidates[0], nil
+	}
+	var total uint32
+	for _, c := range candidates {
+		total += weightOf(c)
+	}
+	if total == 0 { // 理论不达(weightOf>=1),兜底
+		return candidates[0], nil
+	}
+	h := fnv.New32a()
+	_, _ = h.Write([]byte(hint.OutTradeNo))
+	target := h.Sum32() % total
+	var acc uint32
+	for _, c := range candidates {
+		acc += weightOf(c)
+		if target < acc {
+			return c, nil
+		}
+	}
+	return candidates[len(candidates)-1], nil // 浮点无关的整数走位,兜底不达
+}
+
+func weightOf(c config.AccountConfig) uint32 {
+	if c.Weight <= 0 {
+		return 1
+	}
+	return uint32(c.Weight)
+}