package eval

import (
	"os"

	"github.com/elves/elvish/pkg/eval/vars"
)

// PwdVariable is a variable whose value always reflects the current working
// directory. Setting it changes the current working directory.
type PwdVariable struct {
	ev *Evaler
}

var _ vars.Var = PwdVariable{}

// Getwd allows for unit test error injection.
var getwd func() (string, error) = os.Getwd

// Get returns the current working directory. It returns "/unknown/pwd" when
// it cannot be determined.
func (PwdVariable) Get() interface{} {
	pwd, err := getwd()
	if err != nil {
		return "/unknown/pwd"
	}
	return pwd
}

// Set changes the current working directory.
func (pwd PwdVariable) Set(v interface{}) error {
	path, ok := v.(string)
	if !ok {
		return ErrPathMustBeString
	}
	return pwd.ev.Chdir(path)
}