package mount

import (
	"encoding/json"
	"path/filepath"
	"strings"

	"github.com/Microsoft/hcsshim"
	"github.com/pkg/errors"
)

var (
	// ErrNotImplementOnWindows is returned when an action is not implemented for windows
	ErrNotImplementOnWindows = errors.New("not implemented under windows")
)

// Mount to the provided target
func (m *Mount) Mount(target string) error {
	home, layerID := filepath.Split(m.Source)

	parentLayerPaths, err := m.GetParentPaths()
	if err != nil {
		return err
	}

	var di = hcsshim.DriverInfo{
		HomeDir: home,
	}

	if err = hcsshim.ActivateLayer(di, layerID); err != nil {
		return errors.Wrapf(err, "failed to activate layer %s", m.Source)
	}
	defer func() {
		if err != nil {
			hcsshim.DeactivateLayer(di, layerID)
		}
	}()

	if err = hcsshim.PrepareLayer(di, layerID, parentLayerPaths); err != nil {
		return errors.Wrapf(err, "failed to prepare layer %s", m.Source)
	}
	return nil
}

// ParentLayerPathsFlag is the options flag used to represent the JSON encoded
// list of parent layers required to use the layer
const ParentLayerPathsFlag = "parentLayerPaths="

// GetParentPaths of the mount
func (m *Mount) GetParentPaths() ([]string, error) {
	var parentLayerPaths []string
	for _, option := range m.Options {
		if strings.HasPrefix(option, ParentLayerPathsFlag) {
			err := json.Unmarshal([]byte(option[len(ParentLayerPathsFlag):]), &parentLayerPaths)
			if err != nil {
				return nil, errors.Wrap(err, "failed to unmarshal parent layer paths from mount")
			}
		}
	}
	return parentLayerPaths, nil
}

// Unmount the mount at the provided path
func Unmount(mount string, flags int) error {
	var (
		home, layerID = filepath.Split(mount)
		di            = hcsshim.DriverInfo{
			HomeDir: home,
		}
	)

	if err := hcsshim.UnprepareLayer(di, layerID); err != nil {
		return errors.Wrapf(err, "failed to unprepare layer %s", mount)
	}
	if err := hcsshim.DeactivateLayer(di, layerID); err != nil {
		return errors.Wrapf(err, "failed to deactivate layer %s", mount)
	}

	return nil
}

// UnmountAll unmounts from the provided path
func UnmountAll(mount string, flags int) error {
	return Unmount(mount, flags)
}