// ApplyDiff applies the new layer on top of the root, if parent does not exist with will return a ErrApplyDiffFallback error.
func (d *Driver) ApplyDiff(id string, parent string, diff archive.Reader) (size int64, err error) {
	dir := d.dir(id)

	if parent == "" {
		return 0, ErrApplyDiffFallback
	}

	parentRootDir := path.Join(d.dir(parent), "root")
	if _, err := os.Stat(parentRootDir); err != nil {
		return 0, ErrApplyDiffFallback
	}

	// We now know there is a parent, and it has a "root" directory containing
	// the full root filesystem. We can just hardlink it and apply the
	// layer. This relies on two things:
	// 1) ApplyDiff is only run once on a clean (no writes to upper layer) container
	// 2) ApplyDiff doesn't do any in-place writes to files (would break hardlinks)
	// These are all currently true and are not expected to break

	tmpRootDir, err := ioutil.TempDir(dir, "tmproot")
	if err != nil {
		return 0, err
	}
	defer func() {
		if err != nil {
			os.RemoveAll(tmpRootDir)
		} else {
			os.RemoveAll(path.Join(dir, "upper"))
			os.RemoveAll(path.Join(dir, "work"))
			os.RemoveAll(path.Join(dir, "merged"))
			os.RemoveAll(path.Join(dir, "lower-id"))
		}
	}()

	if err = copyDir(parentRootDir, tmpRootDir, copyHardlink); err != nil {
		return 0, err
	}

	options := &archive.TarOptions{UIDMaps: d.uidMaps, GIDMaps: d.gidMaps}
	if size, err = chrootarchive.ApplyUncompressedLayer(tmpRootDir, diff, options); err != nil {
		return 0, err
	}

	rootDir := path.Join(dir, "root")
	if err := os.Rename(tmpRootDir, rootDir); err != nil {
		return 0, err
	}

	return
}

// ApplyDiff extracts the changeset from the given diff into the
// layer with the specified id and parent, returning the size of the
// new layer in bytes.
// The layer should not be mounted when calling this function
func (d *Driver) ApplyDiff(id, parent string, diff archive.Reader) (int64, error) {
	if d.info.Flavour == diffDriver {
		start := time.Now().UTC()
		logrus.Debugf("WindowsGraphDriver ApplyDiff: Start untar layer")
		destination := d.dir(id)
		destination = filepath.Dir(destination)
		size, err := chrootarchive.ApplyUncompressedLayer(destination, diff, nil)
		if err != nil {
			return 0, err
		}
		logrus.Debugf("WindowsGraphDriver ApplyDiff: Untar time: %vs", time.Now().UTC().Sub(start).Seconds())

		return size, nil
	}

	var layerChain []string
	if parent != "" {
		rPId, err := d.resolveID(parent)
		if err != nil {
			return 0, err
		}
		parentChain, err := d.getLayerChain(rPId)
		if err != nil {
			return 0, err
		}
		parentPath, err := hcsshim.GetLayerMountPath(d.info, rPId)
		if err != nil {
			return 0, err
		}
		layerChain = append(layerChain, parentPath)
		layerChain = append(layerChain, parentChain...)
	}

	size, err := d.importLayer(id, diff, layerChain)
	if err != nil {
		return 0, err
	}

	if err = d.setLayerChain(id, layerChain); err != nil {
		return 0, err
	}

	return size, nil
}

// ApplyDiff extracts the changeset from the given diff into the
// layer with the specified id and parent, returning the size of the
// new layer in bytes.
func (gdw *naiveDiffDriver) ApplyDiff(id, parent string, diff archive.Reader) (size int64, err error) {
	driver := gdw.ProtoDriver

	// Mount the root filesystem so we can apply the diff/layer.
	layerFs, err := driver.Get(id, "")
	if err != nil {
		return
	}
	defer driver.Put(id)

	start := time.Now().UTC()
	logrus.Debugf("Start untar layer")
	if size, err = chrootarchive.ApplyUncompressedLayer(layerFs, diff); err != nil {
		return
	}
	logrus.Debugf("Untar time: %vs", time.Now().UTC().Sub(start).Seconds())

	return
}