var (
	ErrLocked = errors.New("locked")
)

var NoUpdateLastUsed noUpdateLastUsed

type Accessor interface {
	Get(ctx context.Context, id string, opts ...RefOption) (ImmutableRef, error)
	GetFromSnapshotter(ctx context.Context, id string, opts ...RefOption) (ImmutableRef, error)
	New(ctx context.Context, s ImmutableRef, opts ...RefOption) (MutableRef, error)
	GetMutable(ctx context.Context, id string) (MutableRef, error) // Rebase?
}

type Controller interface {
	DiskUsage(ctx context.Context, info client.DiskUsageInfo) ([]*client.UsageInfo, error)
	Prune(ctx context.Context, ch chan client.UsageInfo, info ...client.PruneInfo) error
}

type ExternalRefChecker interface {
	Exists(key string) bool
}

type ExternalRefCheckerFunc func() (ExternalRefChecker, error)

type ImmutableRef interface {
	Ref
	Parent() ImmutableRef
	Finalize(ctx context.Context, commit bool) error // Make sure reference is flushed to driver
	Clone() ImmutableRef
}

type Manager interface {
	Accessor
	Controller
	Close() error
}

type ManagerOpt struct {
	Snapshotter     snapshot.SnapshotterBase
	MetadataStore   *metadata.Store
	PruneRefChecker ExternalRefCheckerFunc
}

type Mountable interface {
	Mount(ctx context.Context, readonly bool) (snapshot.Mountable, error)
}

type MutableRef interface {
	Ref
	Commit(context.Context) (ImmutableRef, error)
}

type Ref interface {
	Mountable
	ID() string
	Release(context.Context) error
	Size(ctx context.Context) (int64, error)
	Metadata() *metadata.StorageItem
}

type RefOption interface{}