[usage] Address nits from #14485

Author: jankeromnes

components/common-go/db/types.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/relvacode/iso8601"
+	"google.golang.org/protobuf/types/known/timestamppb"
 )
 
 func NewVarCharTime(t time.Time) VarcharTime {
@@ -129,3 +130,11 @@ const ISO8601Format = "2006-01-02T15:04:05.000Z"
 func TimeToISO8601(t time.Time) string {
 	return t.UTC().Format(ISO8601Format)
 }
+
+func VarcharTimeToTimestamppb(t VarcharTime) *timestamppb.Timestamp {
+	if !t.IsSet() {
+		return nil
+	}
+
+	return timestamppb.New(t.Time())
+}

components/usage/pkg/apiv1/usage.go

@@ -191,20 +191,12 @@ func (s *UsageService) GetCostCenter(ctx context.Context, in *v1.GetCostCenterRe
 }
 
 func dbCostCenterToAPI(c db.CostCenter) *v1.CostCenter {
-	NextBillingTime := timestamppb.New(c.NextBillingTime.Time())
-	if !c.NextBillingTime.IsSet() {
-		NextBillingTime = nil
-	}
-	BillingCycleStart := timestamppb.New(c.BillingCycleStart.Time())
-	if !c.BillingCycleStart.IsSet() {
-		BillingCycleStart = nil
-	}
 	return &v1.CostCenter{
 		AttributionId:     string(c.ID),
 		SpendingLimit:     c.SpendingLimit,
 		BillingStrategy:   convertBillingStrategyToAPI(c.BillingStrategy),
-		NextBillingTime:   NextBillingTime,
-		BillingCycleStart: BillingCycleStart,
+		NextBillingTime:   common_db.VarcharTimeToTimestamppb(c.NextBillingTime),
+		BillingCycleStart: common_db.VarcharTimeToTimestamppb(c.BillingCycleStart),
 	}
 }
 

components/usage/pkg/db/cost_center.go

@@ -319,9 +319,6 @@ func (c *CostCenterManager) ResetUsage(ctx context.Context, cc CostCenter) (Cost
 
 	now := time.Now().UTC()
 
-	// Resetting the usage always resets the billing cycle start time
-	billingCycleStart := now
-
 	// Default to 1 month from now, if there's no nextBillingTime set on the record.
 	nextBillingTime := now.AddDate(0, 1, 0)
 	if cc.NextBillingTime.IsSet() {
@@ -334,12 +331,12 @@ func (c *CostCenterManager) ResetUsage(ctx context.Context, cc CostCenter) (Cost
 		return CostCenter{}, fmt.Errorf("failed to compute invocie usage record for AttributonID: %s: %w", cc.ID, err)
 	}
 
-	// All fields on the new cost center remain the same, except for CreationTime and NextBillingTime
+	// All fields on the new cost center remain the same, except for BillingCycleStart, NextBillingTime, and CreationTime
 	newCostCenter := CostCenter{
 		ID:                cc.ID,
 		SpendingLimit:     spendingLimit,
 		BillingStrategy:   cc.BillingStrategy,
-		BillingCycleStart: common_db.NewVarCharTime(billingCycleStart),
+		BillingCycleStart: common_db.NewVarCharTime(now),
 		NextBillingTime:   common_db.NewVarCharTime(nextBillingTime),
 		CreationTime:      common_db.NewVarCharTime(now),
 	}