gocui: updating widgets from goroutines

goroutine_widget.go

package main

import (
	"errors"
	"fmt"
	"log"
	"strings"
	"time"

	"github.com/jroimartin/gocui"
)

type StatusbarWidget struct {
	name string
	x, y int
	w    int
	val  float64
}

func NewStatusbarWidget(name string, x, y, w int) *StatusbarWidget {
	return &StatusbarWidget{name: name, x: x, y: y, w: w}
}

func (w *StatusbarWidget) SetVal(val float64) error {
	if val < 0 || val > 1 {
		return errors.New("invalid value")
	}
	w.val = val
	return nil
}

func (w *StatusbarWidget) Val() float64 {
	return w.val
}

func (w *StatusbarWidget) Layout(g *gocui.Gui) error {
	v, err := g.SetView(w.name, w.x, w.y, w.x+w.w, w.y+2)
	if err != nil && err != gocui.ErrUnknownView {
		return err
	}
	v.Clear()

	rep := int(w.val * float64(w.w-1))
	fmt.Fprint(v, strings.Repeat("▒", rep))
	return nil
}

func main() {
	g, err := gocui.NewGui()
	if err != nil {
		log.Panicln(err)
	}
	defer g.Close()

	status := NewStatusbarWidget("status", 1, 1, 50)
	g.SetManager(status)

	if err := g.SetKeybinding("", gocui.KeyCtrlC, gocui.ModNone, quit); err != nil {
		log.Panicln(err)
	}

	go update(g, status)

	if err := g.MainLoop(); err != nil && err != gocui.ErrQuit {
		log.Panicln(err)
	}
}

func quit(g *gocui.Gui, v *gocui.View) error {
	return gocui.ErrQuit
}

func update(g *gocui.Gui, sw *StatusbarWidget) {
	for {
		g.Execute(func(g *gocui.Gui) error {
			val := sw.Val() + 0.05
			if val < 0 || val > 1 {
				return nil
			}
			return sw.SetVal(val)
		})
		time.Sleep(500 * time.Millisecond)
	}
}