refactor: extract helpers to reduce duplication and function length in gateway billing

- Extract resolveChannelPricing to DRY the resolver pattern shared by calculateImageCost/calculateTokenCost
- Remove unnecessary IIFE wrapper and pass accountRateMultiplier as parameter
- Extract resolveBillingMode, resolveMediaType, optionalSubscriptionID to simplify buildRecordUsageLog (104→65 lines)
- Extract shouldDeductAPIKeyQuota/shouldUpdateRateLimits/shouldUpdateAccountQuota methods on postUsageBillingParams to unify duplicated billing conditions

backend/internal/service/gateway_service.go

@@ -7451,6 +7451,18 @@ type postUsageBillingParams struct {
 	APIKeyService         APIKeyQuotaUpdater
 }
 
+func (p *postUsageBillingParams) shouldDeductAPIKeyQuota() bool {
+	return p.Cost.ActualCost > 0 && p.APIKey.Quota > 0 && p.APIKeyService != nil
+}
+
+func (p *postUsageBillingParams) shouldUpdateRateLimits() bool {
+	return p.Cost.ActualCost > 0 && p.APIKey.HasRateLimits() && p.APIKeyService != nil
+}
+
+func (p *postUsageBillingParams) shouldUpdateAccountQuota() bool {
+	return p.Cost.TotalCost > 0 && p.Account.IsAPIKeyOrBedrock() && p.Account.HasAnyQuotaLimit()
+}
+
 // postUsageBilling 统一处理使用量记录后的扣费逻辑：
 //   - 订阅/余额扣费
 //   - API Key 配额更新
@@ -7480,21 +7492,21 @@ func postUsageBilling(ctx context.Context, p *postUsageBillingParams, deps *bill
 	}
 
 	// 2. API Key 配额
-	if cost.ActualCost > 0 && p.APIKey.Quota > 0 && p.APIKeyService != nil {
+	if p.shouldDeductAPIKeyQuota() {
 		if err := p.APIKeyService.UpdateQuotaUsed(billingCtx, p.APIKey.ID, cost.ActualCost); err != nil {
 			slog.Error("update api key quota failed", "api_key_id", p.APIKey.ID, "error", err)
 		}
 	}
 
 	// 3. API Key 限速用量
-	if cost.ActualCost > 0 && p.APIKey.HasRateLimits() && p.APIKeyService != nil {
+	if p.shouldUpdateRateLimits() {
 		if err := p.APIKeyService.UpdateRateLimitUsage(billingCtx, p.APIKey.ID, cost.ActualCost); err != nil {
 			slog.Error("update api key rate limit usage failed", "api_key_id", p.APIKey.ID, "error", err)
 		}
 	}
 
 	// 4. 账号配额用量（账号口径：TotalCost × 账号计费倍率）
-	if cost.TotalCost > 0 && p.Account.IsAPIKeyOrBedrock() && p.Account.HasAnyQuotaLimit() {
+	if p.shouldUpdateAccountQuota() {
 		accountCost := cost.TotalCost * p.AccountRateMultiplier
 		if err := deps.accountRepo.IncrementQuotaUsed(billingCtx, p.Account.ID, accountCost); err != nil {
 			slog.Error("increment account quota used failed", "account_id", p.Account.ID, "cost", accountCost, "error", err)
@@ -7576,13 +7588,13 @@ func buildUsageBillingCommand(requestID string, usageLog *UsageLog, p *postUsage
 		cmd.BalanceCost = p.Cost.ActualCost
 	}
 
-	if p.Cost.ActualCost > 0 && p.APIKey.Quota > 0 && p.APIKeyService != nil {
+	if p.shouldDeductAPIKeyQuota() {
 		cmd.APIKeyQuotaCost = p.Cost.ActualCost
 	}
-	if p.Cost.ActualCost > 0 && p.APIKey.HasRateLimits() && p.APIKeyService != nil {
+	if p.shouldUpdateRateLimits() {
 		cmd.APIKeyRateLimitCost = p.Cost.ActualCost
 	}
-	if p.Cost.TotalCost > 0 && p.Account.IsAPIKeyOrBedrock() && p.Account.HasAnyQuotaLimit() {
+	if p.shouldUpdateAccountQuota() {
 		cmd.AccountQuotaCost = p.Cost.TotalCost * p.AccountRateMultiplier
 	}
 
@@ -7879,8 +7891,9 @@ func (s *GatewayService) recordUsageCore(ctx context.Context, input *recordUsage
 	}
 
 	// 创建使用日志
+	accountRateMultiplier := account.BillingRateMultiplier()
 	usageLog := s.buildRecordUsageLog(ctx, input, result, apiKey, user, account, subscription,
-		requestedModel, multiplier, billingType, cacheTTLOverridden, cost, opts)
+		requestedModel, multiplier, accountRateMultiplier, billingType, cacheTTLOverridden, cost, opts)
 
 	if s.cfg != nil && s.cfg.RunMode == config.RunModeSimple {
 		writeUsageLogBestEffort(ctx, s.usageLogRepo, usageLog, "service.gateway")
@@ -7890,9 +7903,7 @@ func (s *GatewayService) recordUsageCore(ctx context.Context, input *recordUsage
 	}
 
 	requestID := usageLog.RequestID
-	accountRateMultiplier := account.BillingRateMultiplier()
-	billingErr := func() error {
-		_, err := applyUsageBilling(ctx, requestID, usageLog, &postUsageBillingParams{
+	_, billingErr := applyUsageBilling(ctx, requestID, usageLog, &postUsageBillingParams{
 		Cost:                  cost,
 		User:                  user,
 		APIKey:                apiKey,
@@ -7903,8 +7914,6 @@ func (s *GatewayService) recordUsageCore(ctx context.Context, input *recordUsage
 		AccountRateMultiplier: accountRateMultiplier,
 		APIKeyService:         input.APIKeyService,
 	}, s.billingDeps(), s.usageBillingRepo)
-		return err
-	}()
 
 	if billingErr != nil {
 		return billingErr
@@ -7964,6 +7973,20 @@ func (s *GatewayService) calculateSoraMediaCost(
 	return s.billingService.CalculateSoraVideoCost(billingModel, soraConfig, multiplier)
 }
 
+// resolveChannelPricing 检查指定模型是否存在渠道级别定价。
+// 返回非 nil 的 ResolvedPricing 表示有渠道定价，nil 表示走默认定价路径。
+func (s *GatewayService) resolveChannelPricing(ctx context.Context, billingModel string, apiKey *APIKey) *ResolvedPricing {
+	if s.resolver == nil || apiKey.Group == nil {
+		return nil
+	}
+	gid := apiKey.Group.ID
+	resolved := s.resolver.Resolve(ctx, PricingInput{Model: billingModel, GroupID: &gid})
+	if resolved.Source == PricingSourceChannel {
+		return resolved
+	}
+	return nil
+}
+
 // calculateImageCost 计算图片生成费用：渠道级别定价优先，否则走按次计费。
 func (s *GatewayService) calculateImageCost(
 	ctx context.Context,
@@ -7972,15 +7995,7 @@ func (s *GatewayService) calculateImageCost(
 	billingModel string,
 	multiplier float64,
 ) *CostBreakdown {
-	hasChannelPricing := false
-	if s.resolver != nil && apiKey.Group != nil {
-		gid := apiKey.Group.ID
-		resolved := s.resolver.Resolve(ctx, PricingInput{Model: billingModel, GroupID: &gid})
-		if resolved.Source == PricingSourceChannel {
-			hasChannelPricing = true
-		}
-	}
-	if hasChannelPricing {
+	if s.resolveChannelPricing(ctx, billingModel, apiKey) != nil {
 		tokens := UsageTokens{
 			InputTokens:       result.Usage.InputTokens,
 			OutputTokens:      result.Usage.OutputTokens,
@@ -8036,12 +8051,9 @@ func (s *GatewayService) calculateTokenCost(
 	var cost *CostBreakdown
 	var err error
 
-	// 优先尝试 Resolver + CalculateCostUnified（仅在有渠道定价时使用）
-	useUnified := false
-	if s.resolver != nil && apiKey.Group != nil {
+	// 优先尝试渠道定价 → CalculateCostUnified
+	if s.resolveChannelPricing(ctx, billingModel, apiKey) != nil {
 		gid := apiKey.Group.ID
-		resolved := s.resolver.Resolve(ctx, PricingInput{Model: billingModel, GroupID: &gid})
-		if resolved.Source == PricingSourceChannel {
 		cost, err = s.billingService.CalculateCostUnified(CostInput{
 			Ctx:            ctx,
 			Model:          billingModel,
@@ -8051,11 +8063,7 @@ func (s *GatewayService) calculateTokenCost(
 			RateMultiplier: multiplier,
 			Resolver:       s.resolver,
 		})
-			useUnified = true
-		}
-	}
-	if !useUnified {
-		if opts.LongContextThreshold > 0 {
+	} else if opts.LongContextThreshold > 0 {
 		// 长上下文双倍计费（如 Gemini 200K 阈值）
 		cost, err = s.billingService.CalculateCostWithLongContext(
 			billingModel, tokens, multiplier,
@@ -8064,7 +8072,6 @@ func (s *GatewayService) calculateTokenCost(
 	} else {
 		cost, err = s.billingService.CalculateCost(billingModel, tokens, multiplier)
 	}
-	}
 	if err != nil {
 		logger.LegacyPrintf("service.gateway", "Calculate cost failed: %v", err)
 		return &CostBreakdown{ActualCost: 0}
@@ -8083,21 +8090,13 @@ func (s *GatewayService) buildRecordUsageLog(
 	subscription *UserSubscription,
 	requestedModel string,
 	multiplier float64,
+	accountRateMultiplier float64,
 	billingType int8,
 	cacheTTLOverridden bool,
 	cost *CostBreakdown,
 	opts *recordUsageOpts,
 ) *UsageLog {
 	durationMs := int(result.Duration.Milliseconds())
-	var imageSize *string
-	if result.ImageSize != "" {
-		imageSize = &result.ImageSize
-	}
-	var mediaType *string
-	if opts.EnableClaudePath && strings.TrimSpace(result.MediaType) != "" {
-		mediaType = &result.MediaType
-	}
-	accountRateMultiplier := account.BillingRateMultiplier()
 	requestID := resolveUsageBillingRequestID(ctx, result.RequestID)
 	usageLog := &UsageLog{
 		UserID:                user.ID,
@@ -8120,15 +8119,20 @@ func (s *GatewayService) buildRecordUsageLog(
 		RateMultiplier:        multiplier,
 		AccountRateMultiplier: &accountRateMultiplier,
 		BillingType:           billingType,
+		BillingMode:           resolveBillingMode(opts, result, cost),
 		Stream:                result.Stream,
 		DurationMs:            &durationMs,
 		FirstTokenMs:          result.FirstTokenMs,
 		ImageCount:            result.ImageCount,
-		ImageSize:             imageSize,
-		MediaType:             mediaType,
+		ImageSize:             optionalTrimmedStringPtr(result.ImageSize),
+		MediaType:             resolveMediaType(opts, result),
 		CacheTTLOverridden:    cacheTTLOverridden,
 		ChannelID:             optionalInt64Ptr(input.ChannelID),
 		ModelMappingChain:     optionalTrimmedStringPtr(input.ModelMappingChain),
+		UserAgent:             optionalTrimmedStringPtr(input.UserAgent),
+		IPAddress:             optionalTrimmedStringPtr(input.IPAddress),
+		GroupID:               apiKey.GroupID,
+		SubscriptionID:        optionalSubscriptionID(subscription),
 		CreatedAt:             time.Now(),
 	}
 	if cost != nil {
@@ -8141,41 +8145,41 @@ func (s *GatewayService) buildRecordUsageLog(
 		usageLog.ActualCost = cost.ActualCost
 	}
 
-	// 设置计费模式：Sora 媒体类型自身已确定计费模式（由上游处理），跳过
+	return usageLog
+}
+
+// resolveBillingMode 根据计费结果和请求类型确定计费模式。
+// Sora 媒体类型自身已确定计费模式（由上游处理），返回 nil 跳过。
+func resolveBillingMode(opts *recordUsageOpts, result *ForwardResult, cost *CostBreakdown) *string {
 	isSoraMedia := opts.EnableClaudePath &&
 		(result.MediaType == MediaTypeImage || result.MediaType == MediaTypeVideo || result.MediaType == MediaTypePrompt)
-	if !isSoraMedia {
-		if cost != nil && cost.BillingMode != "" {
-			billingMode := cost.BillingMode
-			usageLog.BillingMode = &billingMode
-		} else if result.ImageCount > 0 {
-			billingMode := string(BillingModeImage)
-			usageLog.BillingMode = &billingMode
-		} else {
-			billingMode := string(BillingModeToken)
-			usageLog.BillingMode = &billingMode
-		}
+	if isSoraMedia {
+		return nil
 	}
-
-	// 添加 UserAgent
-	if input.UserAgent != "" {
-		usageLog.UserAgent = &input.UserAgent
+	var mode string
+	switch {
+	case cost != nil && cost.BillingMode != "":
+		mode = cost.BillingMode
+	case result.ImageCount > 0:
+		mode = string(BillingModeImage)
+	default:
+		mode = string(BillingModeToken)
 	}
+	return &mode
+}
 
-	// 添加 IPAddress
-	if input.IPAddress != "" {
-		usageLog.IPAddress = &input.IPAddress
+func resolveMediaType(opts *recordUsageOpts, result *ForwardResult) *string {
+	if opts.EnableClaudePath && strings.TrimSpace(result.MediaType) != "" {
+		return &result.MediaType
 	}
+	return nil
+}
 
-	// 添加分组和订阅关联
-	if apiKey.GroupID != nil {
-		usageLog.GroupID = apiKey.GroupID
-	}
+func optionalSubscriptionID(subscription *UserSubscription) *int64 {
 	if subscription != nil {
-		usageLog.SubscriptionID = &subscription.ID
+		return &subscription.ID
 	}
-
-	return usageLog
+	return nil
 }
 
 // ResolveChannelMapping 委托渠道服务解析模型映射