main.go

package main

import (
	"fmt"
	"math/rand"
	"time"

	"github.com/vbauerster/mpb/v7"
	"github.com/vbauerster/mpb/v7/decor"
)

func init() {
	rand.Seed(time.Now().UnixNano())
}

func main() {
	numBars := 4
	p := mpb.New()

	for i := 0; i < numBars; i++ {
		task := fmt.Sprintf("Task#%02d:", i)
		queue := make([]*mpb.Bar, 2)
		queue[0] = p.AddBar(rand.Int63n(201)+100,
			mpb.PrependDecorators(
				decor.Name(task, decor.WC{W: len(task) + 1, C: decor.DidentRight}),
				decor.Name("downloading", decor.WCSyncSpaceR),
				decor.CountersNoUnit("%d / %d", decor.WCSyncWidth),
			),
			mpb.AppendDecorators(decor.Percentage(decor.WC{W: 5})),
		)
		queue[1] = p.AddBar(rand.Int63n(101)+100,
			mpb.BarQueueAfter(queue[0], false), // this bar is queued
			mpb.BarFillerClearOnComplete(),
			mpb.PrependDecorators(
				decor.Name(task, decor.WC{W: len(task) + 1, C: decor.DidentRight}),
				decor.OnComplete(decor.Name("\x1b[31minstalling\x1b[0m", decor.WCSyncSpaceR), "done!"),
				decor.OnComplete(decor.EwmaETA(decor.ET_STYLE_MMSS, 0, decor.WCSyncWidth), ""),
			),
			mpb.AppendDecorators(
				decor.OnComplete(decor.Percentage(decor.WC{W: 5}), ""),
			),
		)

		go func() {
			for _, b := range queue {
				complete(b)
			}
		}()
	}

	p.Wait()
}

func complete(bar *mpb.Bar) {
	max := 100 * time.Millisecond
	for !bar.Completed() {
		// start variable is solely for EWMA calculation
		// EWMA's unit of measure is an iteration's duration
		start := time.Now()
		time.Sleep(time.Duration(rand.Intn(10)+1) * max / 10)
		bar.IncrInt64(rand.Int63n(5) + 1)
		// we need to call DecoratorEwmaUpdate to fulfill ewma decorator's contract
		bar.DecoratorEwmaUpdate(time.Since(start))
	}
}