package sandbox

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

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

type MountTmpfs struct {
	Path string
	Size int
	Mode os.FileMode
}

func (t *MountTmpfs) apply() error {
	if !path.IsAbs(t.Path) || t.Size < 0 || t.Size > math.MaxUint>>1 {
		return syscall.EBADE
	}
	target := toSysroot(t.Path)
	if err := os.MkdirAll(target, 0755); err != nil {
		return err
	}
	opt := fmt.Sprintf("mode=%#o", t.Mode)
	if t.Size > 0 {
		opt += fmt.Sprintf(",size=%d", t.Mode)
	}
	return syscall.Mount("tmpfs", target, "tmpfs",
		syscall.MS_NOSUID|syscall.MS_NODEV,
		opt)
}

func (t *MountTmpfs) Is(op FSOp) 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 *Filesystem) Tmpfs(dest string, size int, mode os.FileMode) *Filesystem {
	*f = append(*f, &MountTmpfs{dest, size, mode})
	return f
}