// 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/pkg/interpreter"
)

// Track the reductions made by a reduction process.
type Explanation struct {
	reducer interpreter.Interpreter
}

// Attaches a new explanation tracker to a reducer.
func NewExplanation(r interpreter.Interpreter) *Explanation {
	plugin := &Explanation{reducer: r}
	r.On(interpreter.StartEvent, plugin.Start)
	r.On(interpreter.StepEvent, plugin.Step)

	return plugin
}

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

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