package debruijn

import (
	"strconv"
	"strings"
)

type stringifyVisitor struct {
	builder strings.Builder
}

func (v *stringifyVisitor) VisitVariable(a *Variable) {
	v.builder.WriteString(strconv.Itoa(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(')')
}

// Stringify converts a De Bruijn expression to its string representation.
func Stringify(e Expression) string {
	b := &stringifyVisitor{builder: strings.Builder{}}
	e.Accept(b)
	return b.builder.String()
}