parent item mutations

pkg/cart/cart-mutation-helper.go

@@ -2,9 +2,11 @@ package cart
 
 import (
 	"context"
+	"log"
 	"time"
 
 	"git.k6n.net/mats/go-cart-actor/pkg/actor"
+	cart_messages "git.k6n.net/mats/go-cart-actor/proto/cart"
 	"git.k6n.net/mats/platform/inventory"
 )
 
@@ -71,6 +73,73 @@ func (c *CartMutationContext) ReleaseItem(ctx context.Context, cartId CartId, sk
 	return c.reservationService.Release(ctx, inventory.SKU(sku), l, inventory.CartID(cartId.String()))
 }
 
+// CascadeChildQuantities scales every direct child's quantity
+// proportionally when a parent's quantity is bumped (ChangeQuantity or
+// the AddItem-merge path).
+//
+//   - Ratio: newChildQty = oldChildQty × newParentQty / oldParentQty.
+//   - Floor: scale-down via integer division can yield 0 (e.g. parent
+//     2 → 1, child qty 1 → (1×1)/2 = 0). We clamp to 1 so a scale-down
+//     never silently deletes an accessory. The mismatch is acceptable —
+//     shipping one extra child is better than dropping one.
+//   - Reservations: each child's reservation is released then re-acquired
+//     at the new quantity if UseReservations is true for that child AND a
+//     prior reservation existed. A failing reservation is logged, not
+//     raised, so a single bad child doesn't abort the whole cascade
+//     (matches the existing removal pattern in mutation_items.go).
+//   - Recursion: descends into grandchildren using the child's own
+//     before/after quantities as the next ratio's input, so deeply
+//     nested accessory trees (parent → child → grandchild) stay in
+//     ratio with the top-level change.
+//
+// Caller is responsible for locking any grain mutex and for re-running
+// UpdateTotals after the cascade has settled.
+func (c *CartMutationContext) CascadeChildQuantities(
+	ctx context.Context,
+	g *CartGrain,
+	parentLineId uint32,
+	oldParentQty uint16,
+	newParentQty uint16,
+) {
+	if oldParentQty == 0 || oldParentQty == newParentQty {
+		return
+	}
+
+	for _, it := range g.Items {
+		if it == nil {
+			continue
+		}
+		if it.ParentId == nil || *it.ParentId != parentLineId {
+			continue
+		}
+		oldChildQty := it.Quantity
+		ratio := uint32(newParentQty) * uint32(oldChildQty) / uint32(oldParentQty)
+		newChildQty := uint16(ratio)
+		if newChildQty == 0 {
+			newChildQty = 1
+		}
+		if newChildQty == oldChildQty {
+			continue
+		}
+
+		if g.Type == cart_messages.CartType_REGULAR && c.UseReservations(it) && it.ReservationEndTime != nil {
+			if err := c.ReleaseItem(ctx, g.Id, it.Sku, it.StoreId); err != nil {
+				log.Printf("CascadeChildQuantities: failed to release %s: %v", it.Sku, err)
+			}
+			endTime, err := c.ReserveItem(ctx, g.Id, it.Sku, it.StoreId, newChildQty)
+			if err != nil {
+				log.Printf("CascadeChildQuantities: failed to reserve %s at qty %d: %v", it.Sku, newChildQty, err)
+			} else if endTime != nil {
+				it.ReservationEndTime = endTime
+			}
+		}
+
+		it.Quantity = newChildQty
+		// Descend so grandchildren track this child's ratio.
+		c.CascadeChildQuantities(ctx, g, it.Id, oldChildQty, newChildQty)
+	}
+}
+
 func NewCartMultationRegistry(context *CartMutationContext) actor.MutationRegistry {
 
 	reg := actor.NewMutationRegistry()