package image
 

 import (
 	"runtime"
 
 	"github.com/Sirupsen/logrus"
 	"github.com/docker/docker/layer"
 )

 // TypeLayers is used for RootFS.Type for filesystems organized into layers.
 const TypeLayers = "layers"
 

 // typeLayersWithBase is an older format used by Windows up to v1.12. We
 // explicitly handle this as an error case to ensure that a daemon which still
 // has an older image like this on disk can still start, even though the
 // image itself is not usable. See https://github.com/docker/docker/pull/25806.
 const typeLayersWithBase = "layers+base"
 

 // RootFS describes images root filesystem
 // This is currently a placeholder that only supports layers. In the future
 // this can be made into an interface that supports different implementations.
 type RootFS struct {
 	Type    string         `json:"type"`
 	DiffIDs []layer.DiffID `json:"diff_ids,omitempty"`
 }
 

 // NewRootFS returns empty RootFS struct
 func NewRootFS() *RootFS {
 	return &RootFS{Type: TypeLayers}
 }
 

 // Append appends a new diffID to rootfs
 func (r *RootFS) Append(id layer.DiffID) {
 	r.DiffIDs = append(r.DiffIDs, id)
 }

 
 // ChainID returns the ChainID for the top layer in RootFS.
 func (r *RootFS) ChainID() layer.ChainID {

 	if runtime.GOOS == "windows" && r.Type == typeLayersWithBase {
 		logrus.Warnf("Layer type is unsupported on this platform. DiffIDs: '%v'", r.DiffIDs)
 		return ""
 	}

 	return layer.CreateChainID(r.DiffIDs)
 }