package saccharine

import (
	"fmt"
	"strings"
)

func stringifyAtom(n *Variable) string {
	return n.Name
}

func stringifyAbstraction(n *Abstraction) string {
	return "\\" + strings.Join(n.Parameters, " ") + "." + Stringify(n.Body)
}

func stringifyApplication(n *Application) string {
	arguments := []string{Stringify(n.Abstraction)}

	for _, argument := range n.Arguments {
		arguments = append(arguments, Stringify(argument))
	}

	return "(" + strings.Join(arguments, " ") + ")"
}

func stringifyLet(s *LetStatement) string {
	return s.Name + " " + strings.Join(s.Parameters, " ") + " := " + Stringify(s.Body)
}

func stringifyDeclare(s *DeclareStatement) string {
	return Stringify(s.Value)
}

func stringifyStatement(s Statement) string {
	switch s := s.(type) {
	case *DeclareStatement:
		return stringifyDeclare(s)
	case *LetStatement:
		return stringifyLet(s)
	default:
		panic(fmt.Errorf("unknown statement type: %v", s))
	}
}

func stringifyClause(n *Clause) string {
	stmts := ""

	for _, statement := range n.Statements {
		stmts += stringifyStatement(statement) + "; "
	}

	return "{ " + stmts + Stringify(n.Returns) + " }"
}

// Convert an expression back into valid source code.
func Stringify(n Expression) string {
	switch n := n.(type) {
	case *Variable:
		return stringifyAtom(n)
	case *Abstraction:
		return stringifyAbstraction(n)
	case *Application:
		return stringifyApplication(n)
	case *Clause:
		return stringifyClause(n)
	default:
		panic(fmt.Errorf("unknown expression type: %T", n))
	}
}