package engine

import (
	"git.maximhutz.com/max/lambda/internal/config"
	"git.maximhutz.com/max/lambda/pkg/debruijn"
	"git.maximhutz.com/max/lambda/pkg/emitter"
)

// A process for reducing one λ-expression using De Bruijn indices.
type DeBruijnEngine struct {
	Config     *config.Config
	Expression *debruijn.Expression
	emitter.Emitter
}

// NewDeBruijnEngine creates a new De Bruijn engine.
func NewDeBruijnEngine(config *config.Config, expression interface{}) *DeBruijnEngine {
	expr := expression.(*debruijn.Expression)
	return &DeBruijnEngine{Config: config, Expression: expr}
}

// Run begins the reduction process.
func (e *DeBruijnEngine) Run() {
	e.Emit("start")

	debruijn.ReduceAll(e.Expression, func() {
		e.Emit("step")
	})

	e.Emit("end")
}

// GetResult returns the stringified result.
func (e *DeBruijnEngine) GetResult() string {
	return debruijn.Stringify(*e.Expression)
}