go-cart-actor/pkg/cart/cart-mutation-helper.go

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"
)

type CartMutationContext struct {
	reservationService inventory.ReservationPolicy
}

func NewCartMutationContext(reservationService inventory.ReservationPolicy) *CartMutationContext {
	return &CartMutationContext{
		reservationService: reservationService,
	}
}

func (c *CartMutationContext) ReserveItem(ctx context.Context, cartId CartId, sku string, locationId *string, quantity uint16) (*time.Time, error) {

	if quantity <= 0 || c.reservationService == nil {
		return nil, nil
	}

	l := inventory.LocationID("se")
	if locationId != nil {
		l = inventory.LocationID(*locationId)
	}
	ttl := time.Minute * 15
	endTime := time.Now().Add(ttl)
	err := c.reservationService.Reserve(ctx, inventory.CartReserveRequest{
		CartID: inventory.CartID(cartId.String()),
		InventoryReference: &inventory.InventoryReference{
			SKU:        inventory.SKU(sku),
			LocationID: l,
		},
		TTL:      ttl,
		Quantity: uint32(quantity),
	})
	if err != nil {
		return nil, err
	}

	return &endTime, nil

}

func (c *CartMutationContext) UseReservations(item *CartItem) bool {
	if item.ReservationEndTime != nil {
		return true
	}
	if item.DropShip {
		return false
	}
	if item.InventoryTracked {
		return true
	}
	return false
}

func (c *CartMutationContext) ReleaseItem(ctx context.Context, cartId CartId, sku string, locationId *string) error {
	if c.reservationService == nil {
		return nil
	}
	l := inventory.LocationID("se")
	if locationId != nil {
		l = inventory.LocationID(*locationId)
	}
	return c.reservationService.Release(ctx, inventory.SKU(sku), l, inventory.CartID(cartId.String()))
}

// equalOptional is the canonical nullable-equality primitive used by the
// cart mutations when deciding whether two identifier fields (parent/child
// links, store ids, anything else nullable) refer to the same thing.
//
// Returns true when both pointers are nil, when both alias the same
// address, or when both are non-nil and dereference to equal values. The
// same-address short-circuit is a no-op for correctness but lets a caller
// who passes the same variable get back true without traversing the
// generic's comparison path.
//
// One tested primitive covers every *T the cart currently compares —
// `*uint32` for ParentId, `*string` for StoreId — and any future
// comparable pointer type. Hand-rolled "both nil OR both non-nil and
// equal" expressions were duplicated at AddItem's merge site and were a
// footgun whenever a new field was added (which axis of the predicate
// was the relevant one?). Keeping a single helper makes future merges
// safer to copy.
func equalOptional[T comparable](a, b *T) bool {
	if a == b { // both nil OR same address
		return true
	}
	if a == nil || b == nil {
		return false
	}
	return *a == *b
}

// 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()
	reg.RegisterMutations(
		actor.NewMutation(context.AddItem),
		actor.NewMutation(context.ChangeQuantity),
		actor.NewMutation(context.RemoveItem),
		actor.NewMutation(ClearCart),
		actor.NewMutation(AddVoucher),
		actor.NewMutation(RemoveVoucher),
		actor.NewMutation(UpsertSubscriptionDetails),
		actor.NewMutation(SetUserId),
		actor.NewMutation(LineItemMarking),
		actor.NewMutation(RemoveLineItemMarking),
		actor.NewMutation(SetLineItemCustomFields),
		actor.NewMutation(SubscriptionAdded),
		actor.NewMutation(context.SetCartType),
		actor.NewMutation(SetRecoveryContact),
		//		actor.NewMutation(SubscriptionRemoved),
	)
	return reg

}