package blk

import (
	"bytes"
	"encoding/json"
	"regexp"
	"strings"

	"github.com/go-errors/errors"
	"golang.org/x/exp/slices"

	"gensokyo.cafe/xmnt/cfg"
	"gensokyo.cafe/xmnt/mnt"
	"gensokyo.cafe/xmnt/msg"
	"gensokyo.cafe/xmnt/util"
)

type FSType string

const FSTypeLuks = FSType("crypto_LUKS")

type DevNum string

var supportedFsTypes = []FSType{
	"ext2", "ext3", "ext4", "xfs", "vfat", "ntfs", FSTypeLuks,
}

type BlkDev struct {
	Name       *string   `json:"name"`
	PKName     *string   `json:"pkname"` // name of parent device
	Path       *string   `json:"path"`
	FSType     *FSType   `json:"fstype"`
	MountPoint *string   `json:"mountpoint"`
	UUID       *string   `json:"uuid"`
	DevNum     *DevNum   `json:"maj:min"`
	Children   []*BlkDev `json:"children"`
}

func (b *BlkDev) IsSupportedType() bool {
	if b.FSType == nil {
		return false
	}
	return slices.Contains(supportedFsTypes, *b.FSType)
}

func (b *BlkDev) NeedsDecryption() bool {
	if b.FSType == nil || *b.FSType != FSTypeLuks {
		return false
	}
	return len(b.Children) == 0
}

func (b *BlkDev) IsMounted() bool {
	if b.MountPoint != nil && (*b.MountPoint)[:1] == "/" {
		return true
	}
	for _, child := range b.Children {
		if child.IsMounted() {
			return true
		}
	}
	return false
}

func flattenBlkDevs(devs []*BlkDev) []*BlkDev {
	var ret []*BlkDev
	for _, dev := range devs {
		ret = append(ret, dev)
		ret = append(ret, flattenBlkDevs(dev.Children)...)
	}
	return ret
}

func List(path string) ([]*BlkDev, error) {
	lsblkArgs := []string{"-JT", "-o", "name,pkname,path,fstype,mountpoint,uuid"}
	if path != "" {
		lsblkArgs = append(lsblkArgs, path)
	}

	output, err := util.RunCommand("lsblk", nil, lsblkArgs...)
	if err != nil {
		return nil, errors.WrapPrefix(err, "cannot obtain list of block devices", 0)
	}
	resp := struct {
		BlockDevices []*BlkDev `json:"blockdevices"`
	}{}
	if err := json.Unmarshal(output, &resp); err != nil {
		return nil, errors.WrapPrefix(err, "cannot parse lsblk output", 0)
	}

	return flattenBlkDevs(resp.BlockDevices), nil
}

type Mounter struct {
	dev    *BlkDev
	preset *mnt.Preset
}

func NewMounterFromPreset(p *mnt.Preset) (mnt.Mounter, error) {
	preset := *p
	if preset.Path == "" {
		return nil, errors.New("preset path is empty")
	}
	if !util.IsValidMountPoint(preset.MountPoint) {
		return nil, errors.Errorf("invalid mount point %q", preset.MountPoint)
	}
	m := &Mounter{
		preset: &preset,
	}
	if err := m.refresh(); err != nil {
		return nil, errors.Wrap(err, 0)
	}
	return m, nil
}

func (m *Mounter) refresh() error {
	devs, err := List(m.preset.Path)
	if err != nil {
		return errors.Wrap(err, 0)
	}
	if len(devs) < 1 {
		return errors.Errorf("block device %q not found", m.preset.Path)
	}
	m.dev = devs[0]
	return nil
}

func escapeDmName(s string) string {
	b := regexp.MustCompile(`\W`).ReplaceAllLiteral([]byte(s), []byte{'_'})
	b = regexp.MustCompile(`_+`).ReplaceAllLiteral(b, []byte{'_'})
	b = bytes.Trim(b, "_")
	return string(b)
}

func (m *Mounter) dmName() string {
	for _, c := range m.dev.Children {
		if strings.HasPrefix(*c.Path, "/dev/mapper/") {
			return *c.Name
		}
	}
	// TODO get from property value of systemd mount unit
	if s := escapeDmName(m.preset.Name); s != "" {
		return s
	}
	return escapeDmName(*m.dev.Path)
}

func (m *Mounter) loadKey() error {
	if !m.dev.NeedsDecryption() {
		return nil
	}
	if m.dev.UUID == nil {
		return errors.Errorf("device %q does not have a UUID", *m.dev.Path)
	}
	dmName := m.dmName()
	if dmName == "" {
		return errors.Errorf("cannot determine device mapper name for device %q", *m.dev.Path)
	}

	cred, err := util.ReadCredentialFile(*m.dev.UUID, cfg.Cfg.CredentialStore)
	if err != nil {
		return errors.Wrap(err, 0)
	}
	msg.Infof("Opening device %q as %q", *m.dev.Path, dmName)
	if _, err := util.RunPrivilegedCommand(
		"cryptsetup", strings.NewReader(cred),
		"luksOpen", *m.dev.Path, dmName,
	); err != nil {
		return errors.WrapPrefix(err, "cannot open luks device", 0)
	}

	return nil
}

func (m *Mounter) mount() error {
	if m.dev.IsMounted() {
		return nil
	}
	if !m.dev.IsSupportedType() || m.dev.NeedsDecryption() {
		return errors.Errorf("cannot mount %q: unsupported filesystem type %q", *m.dev.Path, *m.dev.FSType)
	}
	if len(m.dev.Children) > 1 {
		return errors.Errorf("cannot mount %q: can't handle multiple child devices", *m.dev.Path)
	}

	dev := m.dev
	if len(dev.Children) > 0 {
		dev = dev.Children[0]
	}
	mp := m.preset.MountPoint

	if err := util.SystemdMount(mp); err == nil {
		return nil
	} else if !util.ShouldSkipSdMount(err) {
		return errors.WrapPrefix(err, "cannot mount device", 0)
	}

	msg.Infof("Mounting %q on %q", *dev.Path, mp)
	mountOpts := []string{"-o", "noatime", *dev.Path, mp}
	if _, err := util.RunPrivilegedCommand("mount", nil, mountOpts...); err != nil {
		return errors.WrapPrefix(err, "failed to mount device", 0)
	}

	return nil
}

func (m *Mounter) Mount() (err error) {
	if err = m.loadKey(); err != nil {
		return errors.Wrap(err, 0)
	}
	if err = m.refresh(); err != nil {
		return errors.Wrap(err, 0)
	}
	if err = m.mount(); err != nil {
		return errors.Wrap(err, 0)
	}
	// TODO check

	return nil
}

func (m *Mounter) unmount() error {
	if !m.dev.IsMounted() {
		return nil
	}
	if len(m.dev.Children) > 1 {
		return errors.Errorf("cannot unmount %q: can't handle multiple child devices", *m.dev.Path)
	}

	dev := m.dev
	if len(dev.Children) > 0 {
		dev = dev.Children[0]
	}
	mp := *dev.MountPoint

	if err := util.SystemdUnmount(mp); err == nil {
		return nil
	} else if !util.ShouldSkipSdMount(err) {
		return errors.WrapPrefix(err, "cannot unmount device", 0)
	}

	msg.Infof("Unmounting %q on %q", *dev.Path, mp)
	if _, err := util.RunPrivilegedCommand("umount", nil, mp); err != nil {
		return errors.WrapPrefix(err, "failed to unmount device", 0)
	}

	return nil
}

func (m *Mounter) unloadKey() error {
	if *m.dev.FSType != FSTypeLuks {
		return nil
	}
	if m.dev.NeedsDecryption() {
		return nil
	}

	dmName := m.dmName()
	if dmName == "" {
		return errors.New("cannot determine device mapper name")
	}
	if _, err := util.RunPrivilegedCommand("cryptsetup", nil, "close", dmName); err != nil {
		return errors.WrapPrefix(err, "cannot close luks device", 0)
	}
	return nil
}

func (m *Mounter) Unmount() (err error) {
	if err = m.unmount(); err != nil {
		return errors.Wrap(err, 0)
	}
	if err = m.unloadKey(); err != nil {
		return errors.Wrap(err, 0)
	}
	// TODO check

	return nil
}

func match(s string) ([]*mnt.Preset, error) {
	if s == "" {
		return nil, nil
	}
	devices, err := List("")
	if err != nil {
		return nil, errors.Wrap(err, 0)
	}

	var partialMatch []*BlkDev
	for _, dev := range devices {
		if dev.Name != nil && *dev.Name == s ||
			dev.Path != nil && *dev.Path == s {
			return []*mnt.Preset{{
				Name: s,
				Type: "blk",
				Path: *dev.Path,
			}}, nil
		}
		if dev.Path != nil && strings.HasSuffix(*dev.Path, "/"+s) {
			partialMatch = append(partialMatch, dev)
		}
	}

	var ret []*mnt.Preset
	for _, dev := range partialMatch {
		ret = append(ret, &mnt.Preset{
			Name: s,
			Type: "blk",
			Path: *dev.Path,
		})
	}
	return ret, nil
}

func init() {
	mnt.RegisterMounter("blk", NewMounterFromPreset)
	mnt.RegisterMatcher(match)
}