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

import (
	"fmt"

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

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

// Attaches a new explanation tracker to a process.
func NewExplanation(process *engine.Engine) *Explanation {
	plugin := &Explanation{process: process}
	process.On(engine.StartEvent, plugin.Start)
	process.On(engine.StepEvent, plugin.Step)

	return plugin
}

func (t *Explanation) Start() {
	fmt.Println(t.process.Expression.String())
}

func (t *Explanation) Step() {
	fmt.Println("    =", t.process.Expression.String())
}