fix: use costco-go NetDiscounts utility, bump dep to v0.3.9

go.mod

@@ -3,7 +3,7 @@ module github.com/eshaffer321/monarchmoney-sync-backend
 go 1.25.10
 
 require (
-	github.com/eshaffer321/costco-go v0.3.6
+	github.com/eshaffer321/costco-go v0.3.9
 	github.com/eshaffer321/monarchmoney-go v1.0.5
 	github.com/eshaffer321/walmart-client-go/v2 v2.0.1
 	github.com/go-chi/chi/v5 v5.2.5

go.sum

@@ -2,8 +2,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
-github.com/eshaffer321/costco-go v0.3.6 h1:C8SR/UvgMyFIGBoF8KlugpuTBoCo/khK6zm7QDprUco=
-github.com/eshaffer321/costco-go v0.3.6/go.mod h1:pIIKOjw+KyiQ2+xn9EUdZTIRPbts3b4mU7+OzDY/Jdo=
+github.com/eshaffer321/costco-go v0.3.9 h1:HoRcJHMljCJY1DQECQ4hsM3hzAEAqfzX8CckEwNin9o=
+github.com/eshaffer321/costco-go v0.3.9/go.mod h1:ANJTHfRSPyot9cWKNlfs5qDKRKkA4tYORrorvWx/vbM=
 github.com/eshaffer321/monarchmoney-go v1.0.5 h1:V3iP0bvB1q3+m9Gkl6KBCFL44sNsiHDbTxSOU9fHZco=
 github.com/eshaffer321/monarchmoney-go v1.0.5/go.mod h1:ZKPCYT7NcsKGI+YpJ2EqPtfE3dKfuPbiTUrj6J84ot4=
 github.com/eshaffer321/walmart-client-go/v2 v2.0.1 h1:R8NFqKqfdri02Jhmr6jOMpCLAzjdiRbStLtjGKo6WaA=

internal/adapters/providers/costco/provider.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"log/slog"
-	"strings"
 	"time"
 
 	costcogo "github.com/eshaffer321/costco-go/pkg/costco"
@@ -245,51 +244,23 @@ func (p *Provider) convertReceipt(receipt *costcogo.Receipt, hasDetails bool) pr
 
 	var items []providers.OrderItem
 	if hasDetails {
-		// Build maps to net out discount line items
-		itemMap := make(map[string]*CostcoOrderItem)
-		descMap := make(map[string]*CostcoOrderItem) // fallback: keyed by uppercased description
-
-		// First pass: collect all non-discount items
-		for _, item := range receipt.ItemArray {
-			if !item.IsDiscount() {
-				entry := &CostcoOrderItem{
-					name:        item.ItemDescription01,
-					price:       item.Amount,
-					quantity:    float64(item.Unit),
-					unitPrice:   item.ItemUnitPriceAmount,
-					sku:         item.ItemNumber,
-					description: fmt.Sprintf("%s %s", item.ItemDescription01, item.ItemDescription02),
-				}
-				itemMap[item.ItemNumber] = entry
-				descMap[strings.ToUpper(strings.TrimSpace(item.ItemDescription01))] = entry
-			}
-		}
-
-		// Second pass: apply discounts to parent items
-		for _, item := range receipt.ItemArray {
-			if item.IsDiscount() {
-				parentRef := item.GetParentItemNumber()
-				parentItem, exists := itemMap[parentRef]
-				if !exists {
-					// Costco sometimes references the parent by description (e.g. "/AAA BATTERY")
-					// rather than by item number (e.g. "/1234567").
-					parentItem, exists = descMap[strings.ToUpper(parentRef)]
-				}
-				if exists {
-					parentItem.price += item.Amount
-				} else {
-					p.logger.Warn("found orphaned discount with no matching parent item",
-						"discount_item", item.ItemNumber,
-						"parent_item_ref", parentRef,
-						"discount_amount", item.Amount,
-					)
-				}
-			}
+		netted, orphaned := costcogo.NetDiscounts(receipt.ItemArray)
+		for _, disc := range orphaned {
+			p.logger.Warn("found orphaned discount with no matching parent item",
+				"discount_item", disc.ItemNumber,
+				"parent_item_ref", disc.GetParentItemNumber(),
+				"discount_amount", disc.Amount,
+			)
 		}
-
-		// Convert map to slice
-		for _, item := range itemMap {
-			items = append(items, item)
+		for _, item := range netted {
+			items = append(items, &CostcoOrderItem{
+				name:        item.ItemDescription01,
+				price:       item.Amount,
+				quantity:    float64(item.Unit),
+				unitPrice:   item.ItemUnitPriceAmount,
+				sku:         item.ItemNumber,
+				description: fmt.Sprintf("%s %s", item.ItemDescription01, item.ItemDescription02),
+			})
 		}
 	}
 

internal/adapters/providers/costco/provider_test.go

@@ -500,4 +500,38 @@ func TestConvertReceipt_DiscountNetting(t *testing.T) {
 		assert.Equal(t, "AAA BATTERY", items[0].GetName())
 		assert.Equal(t, 12.49, items[0].GetPrice(), "Discount should be applied via description fallback")
 	})
+
+	t.Run("discount references parent by partial description substring", func(t *testing.T) {
+		// Real receipts sometimes have the parent item named e.g. "AA/AAA BATTERY" but the
+		// discount line references it as "/AAA BATTERY" — neither item-number nor exact
+		// description match will succeed, so we need a substring/contains fallback.
+		receipt := &costcogo.Receipt{
+			TransactionBarcode: "TEST506",
+			TransactionDate:    "2025-10-20",
+			Total:              12.49,
+			SubTotal:           12.49,
+			Taxes:              0.00,
+			ItemArray: []costcogo.ReceiptItem{
+				{
+					ItemNumber:        "379938",
+					ItemDescription01: "AA/AAA BATTERY", // full name differs from discount ref
+					Amount:            14.99,
+					Unit:              1,
+				},
+				{
+					ItemNumber:        "999001",
+					ItemDescription01: "/AAA BATTERY", // partial description ref
+					Amount:            -2.50,
+					Unit:              -1,
+				},
+			},
+		}
+
+		order := provider.convertReceipt(receipt, true)
+		items := order.GetItems()
+
+		require.Len(t, items, 1, "Should have 1 item after netting partial-description-referenced discount")
+		assert.Equal(t, "AA/AAA BATTERY", items[0].GetName())
+		assert.Equal(t, 12.49, items[0].GetPrice(), "Discount should be applied via partial description fallback")
+	})
 }