even more refactoring

mutation_add_item.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/proto"
+)
+
+// mutation_add_item.go
+//
+// Registers the AddItem cart mutation in the generic mutation registry.
+// This replaces the legacy switch-based logic previously found in CartGrain.Apply.
+//
+// Behavior:
+//   * Validates quantity > 0
+//   * If an item with same SKU exists -> increases quantity
+//   * Else creates a new CartItem with computed tax amounts
+//   * Totals recalculated automatically via WithTotals()
+//
+// NOTE: Any future field additions in messages.AddItem that affect pricing / tax
+// must keep this handler in sync.
+
+func init() {
+	RegisterMutation[messages.AddItem](
+		"AddItem",
+		func(g *CartGrain, m *messages.AddItem) error {
+			if m == nil {
+				return fmt.Errorf("AddItem: nil payload")
+			}
+			if m.Quantity < 1 {
+				return fmt.Errorf("AddItem: invalid quantity %d", m.Quantity)
+			}
+
+			// Fast path: merge with existing item having same SKU
+			if existing, found := g.FindItemWithSku(m.Sku); found {
+				existing.Quantity += int(m.Quantity)
+				return nil
+			}
+
+			g.mu.Lock()
+			defer g.mu.Unlock()
+
+			g.lastItemId++
+			taxRate := 2500
+			if m.Tax > 0 {
+				taxRate = int(m.Tax)
+			}
+			taxAmountPerUnit := GetTaxAmount(m.Price, taxRate)
+
+			g.Items = append(g.Items, &CartItem{
+				Id:          g.lastItemId,
+				ItemId:      int(m.ItemId),
+				Quantity:    int(m.Quantity),
+				Sku:         m.Sku,
+				Name:        m.Name,
+				Price:       m.Price,
+				TotalPrice:  m.Price * int64(m.Quantity),
+				TotalTax:    int64(taxAmountPerUnit * int64(m.Quantity)),
+				Image:       m.Image,
+				Stock:       StockStatus(m.Stock),
+				Disclaimer:  m.Disclaimer,
+				Brand:       m.Brand,
+				Category:    m.Category,
+				Category2:   m.Category2,
+				Category3:   m.Category3,
+				Category4:   m.Category4,
+				Category5:   m.Category5,
+				OrgPrice:    m.OrgPrice,
+				ArticleType: m.ArticleType,
+				Outlet:      m.Outlet,
+				SellerId:    m.SellerId,
+				SellerName:  m.SellerName,
+				Tax:         int(taxAmountPerUnit),
+				TaxRate:     taxRate,
+				StoreId:     m.StoreId,
+			})
+
+			return nil
+		},
+		WithTotals(), // Recalculate totals after successful mutation
+	)
+}