per

type Cache interface {
	Get(ctx context.Context, key string, ttl time.Duration, f ComputeFunc) (interface{}, error)
	SetItem(ctx context.Context, item Item, ttl time.Duration)
	BatchGetItems(ctx context.Context, keys []string) Items
	BatchSetItems(ctx context.Context, items Items, ttl time.Duration)
}

type ComputeFunc func(ctx context.Context) (interface{}, error)

type Item struct {
	Key    string
	Value  interface{}
	Delta  time.Duration
	Expiry time.Time
}

type Items []*Item