package sandbox

import (
	"encoding/gob"
	"fmt"
	"math"
	"os"
	"path"
	"syscall"
	"unsafe"
)

func init() { gob.Register(new(BindMount)) }

// BindMount bind mounts host path Source on container path Target.
type BindMount struct {
	Source, Target string

	Flags int
}

func (b *BindMount) apply(*InitParams) error {
	if !path.IsAbs(b.Source) || !path.IsAbs(b.Target) {
		return msg.WrapErr(syscall.EBADE,
			"path is not absolute")
	}
	return bindMount(b.Source, b.Target, b.Flags)
}

func (b *BindMount) Is(op Op) bool { vb, ok := op.(*BindMount); return ok && *b == *vb }
func (b *BindMount) String() string {
	if b.Source == b.Target {
		return fmt.Sprintf("%q flags %#x", b.Source, b.Flags)
	}
	return fmt.Sprintf("%q on %q flags %#x", b.Source, b.Target, b.Flags&BindWritable)
}
func (f *Ops) Bind(source, target string, flags int) *Ops {
	*f = append(*f, &BindMount{source, target, flags | BindRecursive})
	return f
}

func init() { gob.Register(new(MountProc)) }

// MountProc mounts a private proc instance on container Path.
type MountProc struct {
	Path string
}

func (p *MountProc) apply(*InitParams) error {
	if !path.IsAbs(p.Path) {
		return msg.WrapErr(syscall.EBADE,
			fmt.Sprintf("path %q is not absolute", p.Path))
	}

	target := toSysroot(p.Path)
	if err := os.MkdirAll(target, 0755); err != nil {
		return msg.WrapErr(err, err.Error())
	}
	return wrapErrSuffix(syscall.Mount("proc", target, "proc",
		syscall.MS_NOSUID|syscall.MS_NOEXEC|syscall.MS_NODEV, ""),
		fmt.Sprintf("cannot mount proc on %q:", p.Path))
}

func init() { gob.Register(new(MountDev)) }

// MountDev mounts dev on container Path.
type MountDev struct {
	Path string
}

func (d *MountDev) apply(params *InitParams) error {
	if !path.IsAbs(d.Path) {
		return msg.WrapErr(syscall.EBADE,
			fmt.Sprintf("path %q is not absolute", d.Path))
	}
	target := toSysroot(d.Path)

	if err := mountTmpfs("devtmpfs", d.Path, 0, 0755); err != nil {
		return err
	}

	for _, name := range []string{"null", "zero", "full", "random", "urandom", "tty"} {
		if err := bindMount(
			"/dev/"+name, path.Join(d.Path, name),
			BindSource|BindDevices,
		); err != nil {
			return err
		}
	}
	for i, name := range []string{"stdin", "stdout", "stderr"} {
		if err := os.Symlink(
			"/proc/self/fd/"+string(rune(i+'0')),
			path.Join(target, name),
		); err != nil {
			return msg.WrapErr(err, err.Error())
		}
	}
	for _, pair := range [][2]string{
		{"/proc/self/fd", "fd"},
		{"/proc/kcore", "core"},
		{"pts/ptmx", "ptmx"},
	} {
		if err := os.Symlink(pair[0], path.Join(target, pair[1])); err != nil {
			return msg.WrapErr(err, err.Error())
		}
	}

	devPtsPath := path.Join(target, "pts")
	for _, name := range []string{path.Join(target, "shm"), devPtsPath} {
		if err := os.Mkdir(name, 0755); err != nil {
			return msg.WrapErr(err, err.Error())
		}
	}

	if err := syscall.Mount("devpts", devPtsPath, "devpts",
		syscall.MS_NOSUID|syscall.MS_NOEXEC,
		"newinstance,ptmxmode=0666,mode=620"); err != nil {
		return wrapErrSuffix(err,
			fmt.Sprintf("cannot mount devpts on %q:", devPtsPath))
	}

	if params.Flags&FAllowTTY != 0 {
		var buf [8]byte
		if _, _, errno := syscall.Syscall(
			syscall.SYS_IOCTL, 1, syscall.TIOCGWINSZ,
			uintptr(unsafe.Pointer(&buf[0])),
		); errno == 0 {
			if err := bindMount(
				"/proc/self/fd/1", path.Join(d.Path, "console"),
				BindDevices,
			); err != nil {
				return err
			}
		}
	}

	return nil
}

func (d *MountDev) Is(op Op) bool  { vd, ok := op.(*MountDev); return ok && *d == *vd }
func (d *MountDev) String() string { return fmt.Sprintf("dev on %q", d.Path) }
func (f *Ops) Dev(dest string) *Ops {
	*f = append(*f, &MountDev{dest})
	return f
}

func (p *MountProc) Is(op Op) bool  { vp, ok := op.(*MountProc); return ok && *p == *vp }
func (p *MountProc) String() string { return fmt.Sprintf("proc on %q", p.Path) }
func (f *Ops) Proc(dest string) *Ops {
	*f = append(*f, &MountProc{dest})
	return f
}

func init() { gob.Register(new(MountTmpfs)) }

// MountTmpfs mounts tmpfs on container Path.
type MountTmpfs struct {
	Path string
	Size int
	Perm os.FileMode
}

func (t *MountTmpfs) apply(*InitParams) error {
	if !path.IsAbs(t.Path) {
		return msg.WrapErr(syscall.EBADE,
			fmt.Sprintf("path %q is not absolute", t.Path))
	}
	if t.Size < 0 || t.Size > math.MaxUint>>1 {
		return msg.WrapErr(syscall.EBADE,
			fmt.Sprintf("size %d out of bounds", t.Size))
	}
	return mountTmpfs("tmpfs", t.Path, t.Size, t.Perm)
}

func (t *MountTmpfs) Is(op Op) bool  { vt, ok := op.(*MountTmpfs); return ok && *t == *vt }
func (t *MountTmpfs) String() string { return fmt.Sprintf("tmpfs on %q size %d", t.Path, t.Size) }
func (f *Ops) Tmpfs(dest string, size int, perm os.FileMode) *Ops {
	*f = append(*f, &MountTmpfs{dest, size, perm})
	return f
}