// Package "explanation" provides a observer to gather the reasoning during the
// reduction, and present a thorough explanation to the user for each step.
package explanation

import (
	"fmt"

	"git.maximhutz.com/max/lambda/internal/engine"
	"git.maximhutz.com/max/lambda/pkg/lambda"
)

// Track the reductions made by a reduction proess.
type Tracker struct {
	process *engine.Engine
}

// Attaches a new explanation tracker to a process.
func Track(process *engine.Engine) *Tracker {
	tracker := &Tracker{process: process}
	process.On("start", tracker.Start)
	process.On("step", tracker.Step)

	return tracker
}

func (t *Tracker) Start() {
	fmt.Println(lambda.Stringify(*t.process.Expression))
}

func (t *Tracker) Step() {
	fmt.Println("    =", lambda.Stringify(*t.process.Expression))
}