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

var ErrNoBlobs = errors.Errorf("no blobs for snapshot")

var NoUpdateLastUsed noUpdateLastUsed

type Accessor interface {
	GetByBlob(ctx context.Context, desc ocispec.Descriptor, parent ImmutableRef, opts ...RefOption) (ImmutableRef, error)
	Get(ctx context.Context, id string, opts ...RefOption) (ImmutableRef, error)

	New(ctx context.Context, parent ImmutableRef, s session.Group, opts ...RefOption) (MutableRef, error)
	GetMutable(ctx context.Context, id string, opts ...RefOption) (MutableRef, error) // Rebase?
	IdentityMapping() *idtools.IdentityMapping
	Metadata(string) *metadata.StorageItem
}

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 DescHandler struct {
	Provider       func(session.Group) content.Provider
	Progress       progress.Controller
	SnapshotLabels map[string]string
	Ref            string // string representation of desc origin, can be used as a sync key
}

type DescHandlerKey digest.Digest

type DescHandlers map[digest.Digest]*DescHandler

type ExternalRefChecker interface {
	Exists(string, []digest.Digest) bool
}

type ExternalRefCheckerFunc func() (ExternalRefChecker, error)

type ImmutableRef interface {
	Ref
	Parent() ImmutableRef
	Clone() ImmutableRef

	Info() RefInfo
	Extract(ctx context.Context, s session.Group) error // +progress
	GetRemote(ctx context.Context, createIfNeeded bool, compressionType compression.Type, forceCompression bool, s session.Group) (*solver.Remote, error)
}

type Manager interface {
	Accessor
	Controller
	Close() error
}

type ManagerOpt struct {
	Snapshotter     snapshot.Snapshotter
	MetadataStore   *metadata.Store
	ContentStore    content.Store
	LeaseManager    leases.Manager
	PruneRefChecker ExternalRefCheckerFunc
	GarbageCollect  func(ctx context.Context) (gc.Stats, error)
	Applier         diff.Applier
	Differ          diff.Comparer
}

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

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

type NeedsRemoteProvidersError []digest.Digest

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

type RefInfo struct {
	SnapshotID  string
	ChainID     digest.Digest
	BlobChainID digest.Digest
	DiffID      digest.Digest
	Blob        digest.Digest
	MediaType   string
	Extracted   bool
}

type RefOption interface{}

type Unlazier interface {
	Unlazy(ctx context.Context) error
}