spinner.go

package spinner

import (
	"fmt"
	"io"
	"sync"
	"syscall"
	"time"

	"golang.org/x/term"
)

const (
	// 150ms per frame
	DEFAULT_FRAME_RATE = time.Millisecond * 150
)

var DefaultCharset = []string{"|", "/", "-", "\\"}

type Spinner struct {
	sync.Mutex
	Title     string
	Charset   []string
	FrameRate time.Duration
	runChan   chan struct{}
	stopOnce  sync.Once
	Output    io.Writer
	NoTty     bool
}

// create spinner object
func main(title string) *Spinner {
	sp := &Spinner{
		Title:     title,
		Charset:   DefaultCharset,
		FrameRate: DEFAULT_FRAME_RATE,
		runChan:   make(chan struct{}),
	}
	if !term.IsTerminal(int(syscall.Stdout)) {
		sp.NoTty = true
	}
	return sp
}

// start a new spinner, title can be an empty string
func StartNew(title string) *Spinner {
	return main(title).Start()
}

// start spinner
func (sp *Spinner) Start() *Spinner {
	go sp.writer()
	return sp
}

// set custom spinner frame rate
func (sp *Spinner) SetSpeed(rate time.Duration) *Spinner {
	sp.Lock()
	sp.FrameRate = rate
	sp.Unlock()
	return sp
}

// set custom spinner character set
func (sp *Spinner) SetCharset(chars []string) *Spinner {
	sp.Lock()
	sp.Charset = chars
	sp.Unlock()
	return sp
}

// stop and clear the spinner
func (sp *Spinner) Stop() {
	//prevent multiple calls
	sp.stopOnce.Do(func() {
		close(sp.runChan)
		sp.clearLine()
	})
	// Add delay to avoid spinner overlap with next line
	time.Sleep(1 * time.Second)
}

// spinner animation
func (sp *Spinner) animate() {
	var out string
	for i := 0; i < len(sp.Charset); i++ {
		out = sp.Charset[i] + " " + sp.Title
		switch {
		case sp.Output != nil:
			fmt.Fprint(sp.Output, out)
		case !sp.NoTty:
			fmt.Print(out)
		}
		time.Sleep(sp.FrameRate)
		sp.clearLine()
	}
}

// write out spinner animation until runChan is closed
func (sp *Spinner) writer() {
	sp.animate()
	for {
		select {
		case <-sp.runChan:
			return
		default:
			sp.animate()
		}
	}
}

// workaround for Mac OS < 10 compatibility
func (sp *Spinner) clearLine() {
	if !sp.NoTty {
		fmt.Printf("\033[2K")
		fmt.Println()
		fmt.Printf("\033[1A")
	}
}