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, 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
}

// NewReservationPolicyAdapter creates an adapter that satisfies
// platform/inventory.ReservationPolicy by delegating to the Redis-backed
// reservation service.
func NewReservationPolicyAdapter(inner *RedisCartReservationService) *ReservationPolicyAdapter {
	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 translateReservationError(a.inner.Reserve(ctx, CartReserveRequest{
		InventoryReference: &InventoryReference{
			SKU:        SKU(req.SKU),
			LocationID: LocationID(req.LocationID),
		},
		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.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.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
}