// Init returns the a native diff driver for overlay filesystem.
// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.
// If a overlay filesystem is not supported over a existing filesystem then error graphdriver.ErrIncompatibleFS is returned.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	opts, err := parseOptions(options)
	if err != nil {
		return nil, err
	}

	if err := supportsOverlay(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	// require kernel 4.0.0 to ensure multiple lower dirs are supported
	v, err := kernel.GetKernelVersion()
	if err != nil {
		return nil, err
	}
	if kernel.CompareKernelVersion(*v, kernel.VersionInfo{Kernel: 4, Major: 0, Minor: 0}) < 0 {
		if !opts.overrideKernelCheck {
			return nil, graphdriver.ErrNotSupported
		}
		logrus.Warnf("Using pre-4.0.0 kernel for overlay2, mount failures may require kernel update")
	}

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	// check if they are running over btrfs, aufs, zfs, overlay, or ecryptfs
	switch fsMagic {
	case graphdriver.FsMagicBtrfs, graphdriver.FsMagicAufs, graphdriver.FsMagicZfs, graphdriver.FsMagicOverlay, graphdriver.FsMagicEcryptfs:
		logrus.Errorf("'overlay2' is not supported over %s", backingFs)
		return nil, graphdriver.ErrIncompatibleFS
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the driver home dir
	if err := idtools.MkdirAllAs(path.Join(home, linkDir), 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	d := &Driver{
		home:    home,
		uidMaps: uidMaps,
		gidMaps: gidMaps,
		ctr:     graphdriver.NewRefCounter(graphdriver.NewFsChecker(graphdriver.FsMagicOverlay)),
	}

	return d, nil
}

// InitFilter returns a new Windows storage filter driver.
func InitFilter(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	logrus.Debugf("WindowsGraphDriver InitFilter at %s", home)
	d := &Driver{
		info: hcsshim.DriverInfo{
			HomeDir: home,
			Flavour: filterDriver,
		},
		cache: make(map[string]string),
		ctr:   graphdriver.NewRefCounter(&checker{}),
	}
	return d, nil
}

// Init returns the NaiveDiffDriver, a native diff driver for overlay filesystem.
// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.
// If a overlay filesystem is not supported over a existing filesystem then error graphdriver.ErrIncompatibleFS is returned.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {

	if err := supportsOverlay(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	// check if they are running over btrfs, aufs, zfs or overlay
	switch fsMagic {
	case graphdriver.FsMagicBtrfs:
		logrus.Error("'overlay' is not supported over btrfs.")
		return nil, graphdriver.ErrIncompatibleFS
	case graphdriver.FsMagicAufs:
		logrus.Error("'overlay' is not supported over aufs.")
		return nil, graphdriver.ErrIncompatibleFS
	case graphdriver.FsMagicZfs:
		logrus.Error("'overlay' is not supported over zfs.")
		return nil, graphdriver.ErrIncompatibleFS
	case graphdriver.FsMagicOverlay:
		logrus.Error("'overlay' is not supported over overlay.")
		return nil, graphdriver.ErrIncompatibleFS
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the driver home dir
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	d := &Driver{
		home:      home,
		pathCache: make(map[string]string),
		uidMaps:   uidMaps,
		gidMaps:   gidMaps,
		ctr:       graphdriver.NewRefCounter(),
	}

	return NaiveDiffDriverWithApply(d, uidMaps, gidMaps), nil
}

// Init returns the NaiveDiffDriver, a native diff driver for overlay filesystem.
// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.
// If an overlay filesystem is not supported over an existing filesystem then error graphdriver.ErrIncompatibleFS is returned.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {

	if err := supportsOverlay(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	switch fsMagic {
	case graphdriver.FsMagicAufs, graphdriver.FsMagicBtrfs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs, graphdriver.FsMagicEcryptfs:
		logrus.Errorf("'overlay' is not supported over %s", backingFs)
		return nil, graphdriver.ErrIncompatibleFS
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the driver home dir
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	supportsDType, err := fsutils.SupportsDType(home)
	if err != nil {
		return nil, err
	}
	if !supportsDType {
		// not a fatal error until v1.16 (#27443)
		logrus.Warn(overlayutils.ErrDTypeNotSupported("overlay", backingFs))
	}

	d := &Driver{
		home:          home,
		uidMaps:       uidMaps,
		gidMaps:       gidMaps,
		ctr:           graphdriver.NewRefCounter(graphdriver.NewFsChecker(graphdriver.FsMagicOverlay)),
		supportsDType: supportsDType,
	}

	return NaiveDiffDriverWithApply(d, uidMaps, gidMaps), nil
}

// Init creates a driver with the given home and the set of options.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	deviceSet, err := NewDeviceSet(home, true, options, uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	d := &Driver{
		DeviceSet: deviceSet,
		home:      home,
		uidMaps:   uidMaps,
		gidMaps:   gidMaps,
		ctr:       graphdriver.NewRefCounter(graphdriver.NewDefaultChecker()),
	}

	return graphdriver.NewNaiveDiffDriver(d, uidMaps, gidMaps), nil
}

// InitFilter returns a new Windows storage filter driver.
func InitFilter(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	logrus.Debugf("WindowsGraphDriver InitFilter at %s", home)

	fsType, err := getFileSystemType(string(home[0]))
	if err != nil {
		return nil, err
	}
	if strings.ToLower(fsType) == "refs" {
		return nil, fmt.Errorf("%s is on an ReFS volume - ReFS volumes are not supported", home)
	}

	d := &Driver{
		info: hcsshim.DriverInfo{
			HomeDir: home,
			Flavour: filterDriver,
		},
		cache: make(map[string]string),
		ctr:   graphdriver.NewRefCounter(&checker{}),
	}
	return d, nil
}

// Init returns a new ZFS driver.
// It takes base mount path and an array of options which are represented as key value pairs.
// Each option is in the for key=value. 'zfs.fsname' is expected to be a valid key in the options.
func Init(base string, opt []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	var err error

	if _, err := exec.LookPath("zfs"); err != nil {
		logrus.Debugf("[zfs] zfs command is not available: %v", err)
		return nil, graphdriver.ErrPrerequisites
	}

	file, err := os.OpenFile("/dev/zfs", os.O_RDWR, 600)
	if err != nil {
		logrus.Debugf("[zfs] cannot open /dev/zfs: %v", err)
		return nil, graphdriver.ErrPrerequisites
	}
	defer file.Close()

	options, err := parseOptions(opt)
	if err != nil {
		return nil, err
	}
	options.mountPath = base

	rootdir := path.Dir(base)

	if options.fsName == "" {
		err = checkRootdirFs(rootdir)
		if err != nil {
			return nil, err
		}
	}

	if options.fsName == "" {
		options.fsName, err = lookupZfsDataset(rootdir)
		if err != nil {
			return nil, err
		}
	}

	zfs.SetLogger(new(Logger))

	filesystems, err := zfs.Filesystems(options.fsName)
	if err != nil {
		return nil, fmt.Errorf("Cannot find root filesystem %s: %v", options.fsName, err)
	}

	filesystemsCache := make(map[string]bool, len(filesystems))
	var rootDataset *zfs.Dataset
	for _, fs := range filesystems {
		if fs.Name == options.fsName {
			rootDataset = fs
		}
		filesystemsCache[fs.Name] = true
	}

	if rootDataset == nil {
		return nil, fmt.Errorf("BUG: zfs get all -t filesystem -rHp '%s' should contain '%s'", options.fsName, options.fsName)
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, fmt.Errorf("Failed to get root uid/guid: %v", err)
	}
	if err := idtools.MkdirAllAs(base, 0700, rootUID, rootGID); err != nil {
		return nil, fmt.Errorf("Failed to create '%s': %v", base, err)
	}

	if err := mount.MakePrivate(base); err != nil {
		return nil, err
	}
	d := &Driver{
		dataset:          rootDataset,
		options:          options,
		filesystemsCache: filesystemsCache,
		uidMaps:          uidMaps,
		gidMaps:          gidMaps,
		ctr:              graphdriver.NewRefCounter(graphdriver.NewDefaultChecker()),
	}
	return graphdriver.NewNaiveDiffDriver(d, uidMaps, gidMaps), nil
}