feat(v2): limit_aware 策略(UsageSource 留位)+ Router 按配置派发 + config.Routing

internal/accounts/router.go

@@ -0,0 +1,66 @@
+package accounts
+
+import "github.com/wangjia/pay/config"
+
+// Router 是 gateway 面向的 Picker 实现:取候选(EnabledFor)→ 按 hint 排除 → 派发策略。
+// 策略实例进程内单例(round_robin 计数器需长存);未配置/未知策略默认 round_robin。
+type Router struct {
+	reg        *Registry
+	strategies map[string]string // channel -> 策略名
+	byName     map[string]Strategy
+	def        Strategy
+}
+
+// NewRouter 装配路由。routing:channel→策略名(缺省/未知→round_robin);usage=nil→NopUsage。
+// limit_aware 复合 round_robin 作为合格集内的均摊基础策略。
+func NewRouter(reg *Registry, routing map[string]string, usage UsageSource) *Router {
+	rr := NewRoundRobin()
+	byName := map[string]Strategy{
+		StrategyRoundRobin: rr,
+		StrategyWeighted:   NewWeighted(),
+		StrategyLimitAware: NewLimitAware(rr, usage),
+	}
+	cp := map[string]string{}
+	for k, v := range routing {
+		cp[k] = v
+	}
+	return &Router{reg: reg, strategies: cp, byName: byName, def: rr}
+}
+
+func (r *Router) strategyFor(channel string) Strategy {
+	if name, ok := r.strategies[channel]; ok {
+		if s, ok := r.byName[name]; ok {
+			return s
+		}
+	}
+	return r.def // 缺省 / 未知策略名 → round_robin(见计划 D3)
+}
+
+// Pick 实现 accounts.Picker。
+func (r *Router) Pick(channel, region string, hint PickHint) (config.AccountConfig, error) {
+	cands := r.reg.EnabledFor(channel, region)
+	if len(cands) == 0 {
+		return config.AccountConfig{}, ErrNoAccount
+	}
+	if len(hint.ExcludeAccounts) > 0 {
+		if filtered := excludeAccounts(cands, hint.ExcludeAccounts); len(filtered) > 0 {
+			cands = filtered // 过滤到空则保留全集:单账户渠道 retry 仍可用(见计划 D4)
+		}
+	}
+	return r.strategyFor(channel).Pick(channel+"|"+region, cands, hint)
+}
+
+func excludeAccounts(cands []config.AccountConfig, exclude []string) []config.AccountConfig {
+	skip := make(map[string]struct{}, len(exclude))
+	for _, id := range exclude {
+		skip[id] = struct{}{}
+	}
+	out := make([]config.AccountConfig, 0, len(cands))
+	for _, c := range cands {
+		if _, ok := skip[c.AccountID]; ok {
+			continue
+		}
+		out = append(out, c)
+	}
+	return out
+}