package debruijn

import (
	"fmt"
	"strings"
)

type stringifyVisitor struct {
	builder strings.Builder
}

func (v *stringifyVisitor) VisitVariable(a *Variable) {
	if a.label != "" {
		v.builder.WriteString(a.label)
	} else {
		v.builder.WriteString(fmt.Sprintf("%d", a.index))
	}
}

func (v *stringifyVisitor) VisitAbstraction(f *Abstraction) {
	v.builder.WriteRune('\\')
	v.builder.WriteRune('.')
	f.body.Accept(v)
}

func (v *stringifyVisitor) VisitApplication(c *Application) {
	v.builder.WriteRune('(')
	c.abstraction.Accept(v)
	v.builder.WriteRune(' ')
	c.argument.Accept(v)
	v.builder.WriteRune(')')
}

func Stringify(e Expression) string {
	b := &stringifyVisitor{builder: strings.Builder{}}
	e.Accept(b)
	return b.builder.String()
}