package plugins

import (
	"fmt"
	"os"
	"time"

	"git.maximhutz.com/max/lambda/internal/statistics"
	"git.maximhutz.com/max/lambda/pkg/reducer"
)

// An observer, to track reduction performance.
type Statistics struct {
	start time.Time
	steps uint64
}

// Create a new reduction performance Statistics.
func NewStatistics(r reducer.Reducer) *Statistics {
	plugin := &Statistics{}
	r.On(reducer.StartEvent, plugin.Start)
	r.On(reducer.StepEvent, plugin.Step)
	r.On(reducer.StopEvent, plugin.Stop)

	return plugin
}

func (t *Statistics) Start() {
	t.start = time.Now()
	t.steps = 0
}

func (t *Statistics) Step() {
	t.steps++
}

func (t *Statistics) Stop() {
	results := statistics.Results{
		StepsTaken:  t.steps,
		TimeElapsed: uint64(time.Since(t.start).Milliseconds()),
	}

	fmt.Fprint(os.Stderr, results.String())
}