some inventory

pkg/inventory/adapter.go

@@ -2,14 +2,24 @@ package inventory
 
 import (
 	"context"
+	"errors"
 
 	platforminv "git.k6n.net/mats/platform/inventory"
 )
 
 // ReservationPolicyAdapter wraps a RedisCartReservationService to satisfy the
 // platform/inventory.ReservationPolicy interface. It translates between the
-// platform's value types (SKU, LocationID, CartID) and the Redis-level types
-// used internally by go-redis-inventory.
+// platform's value types (SKU, LocationID, CartID, CartReserveRequest,
+// InventoryReference) and the Redis-level types used internally by
+// go-redis-inventory, so that callers (cart, checkout, backoffice, the
+// inventory service itself) can depend on the seam and remain agnostic to the
+// storage substrate — see docs/inventory-shape.md §"Next: inventory service as
+// single writer".
+//
+// The error translation below means callers can `errors.Is(err,
+// platforminv.ErrInsufficientStock)` regardless of whether the underlying
+// storage is Redis Lua (today), an actor grain (the deep rewrite), or
+// something else (the test adapter in platform/inventory/memory.go).
 type ReservationPolicyAdapter struct {
 	inner *RedisCartReservationService
 }
@@ -21,8 +31,13 @@ func NewReservationPolicyAdapter(inner *RedisCartReservationService) *Reservatio
 	return &ReservationPolicyAdapter{inner: inner}
 }
 
+// Compile-time assertion that ReservationPolicyAdapter satisfies the
+// platform/inventory.ReservationPolicy interface. If a method is added or
+// renamed on either side, this stops compiling.
+var _ platforminv.ReservationPolicy = (*ReservationPolicyAdapter)(nil)
+
 func (a *ReservationPolicyAdapter) Reserve(ctx context.Context, req platforminv.CartReserveRequest) error {
-	return a.inner.ReserveForCart(ctx, CartReserveRequest{
+	return translateReservationError(a.inner.Reserve(ctx, CartReserveRequest{
 		InventoryReference: &InventoryReference{
 			SKU:        SKU(req.SKU),
 			LocationID: LocationID(req.LocationID),
@@ -30,13 +45,33 @@ func (a *ReservationPolicyAdapter) Reserve(ctx context.Context, req platforminv.
 		CartID:   CartID(req.CartID),
 		Quantity: req.Quantity,
 		TTL:      req.TTL,
-	})
+	}))
 }
 
 func (a *ReservationPolicyAdapter) Release(ctx context.Context, sku platforminv.SKU, locationID platforminv.LocationID, cartID platforminv.CartID) error {
-	return a.inner.ReleaseForCart(ctx, SKU(sku), LocationID(locationID), CartID(cartID))
+	return a.inner.Release(ctx, SKU(sku), LocationID(locationID), CartID(cartID))
 }
 
 func (a *ReservationPolicyAdapter) Available(ctx context.Context, sku platforminv.SKU, locationID platforminv.LocationID) (int64, error) {
-	return a.inner.GetAvailableInventory(ctx, SKU(sku), LocationID(locationID))
+	return a.inner.Available(ctx, SKU(sku), LocationID(locationID))
+}
+
+// translateReservationError maps the Redis-storage-specific sentinel to the
+// platform-level sentinel so consumers can errors.Is against one set of errors
+// regardless of the underlying ReservationPolicy implementation. Pass-through
+// for unknown errors — those carry enough context on their own.
+//
+// Trade-off: the original Redis sentinel is replaced, not wrapped, so callers
+// that need to discriminate "Redis ran out of stock" from "Lua script timed
+// out" must look inside the seam rather than outside. Per the platform seam
+// contract that's the right cut: storage internals stay encapsulated; callers
+// branch on the cross-module vocabulary.
+func translateReservationError(err error) error {
+	if err == nil {
+		return nil
+	}
+	if errors.Is(err, ErrInsufficientInventory) {
+		return platforminv.ErrInsufficientStock
+	}
+	return err
 }