wtf/modules/cmdrunner/widget.go

package cmdrunner

import (
	"bytes"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"sync"

	"github.com/rivo/tview"
	"github.com/wtfutil/wtf/view"
)

// Widget contains the data for this widget
type Widget struct {
	view.TextWidget

	settings *Settings

	m          sync.Mutex
	buffer     *bytes.Buffer
	runChan    chan bool
	redrawChan chan bool
}

// NewWidget creates a new instance of the widget
func NewWidget(app *tview.Application, settings *Settings) *Widget {
	widget := Widget{
		TextWidget: view.NewTextWidget(app, settings.common),

		settings: settings,
		buffer:   &bytes.Buffer{},
	}

	widget.View.SetWrap(true)
	widget.View.SetScrollable(true)

	widget.runChan = make(chan bool)
	widget.redrawChan = make(chan bool)
	go runCommandLoop(&widget)
	go redrawLoop(&widget)
	widget.runChan <- true

	return &widget
}

// Refresh signals the runCommandLoop to continue, or triggers a re-draw if the
// command is still running.
func (widget *Widget) Refresh() {
	// Try to run the command. If the command is still running, let it keep
	// running and do a refresh instead. Otherwise, the widget will redraw when
	// the command completes.
	select {
	case widget.runChan <- true:
	default:
		widget.redrawChan <- true
	}
}

// String returns the string representation of the widget
func (widget *Widget) String() string {
	args := strings.Join(widget.settings.args, " ")

	if args != "" {
		return fmt.Sprintf("%s %s", widget.settings.cmd, args)
	}

	return widget.settings.cmd
}

func (widget *Widget) Write(p []byte) (n int, err error) {
	widget.m.Lock()
	defer widget.m.Unlock()

	// Write the new data into the buffer
	n, err = widget.buffer.Write(p)

	// Remove lines that exceed maxLines
	lines := widget.countLines()
	if lines > widget.settings.maxLines {
		err = widget.drainLines(lines - widget.settings.maxLines)
	}

	return n, err
}

/* -------------------- Unexported Functions -------------------- */

// countLines counts the lines of data in the buffer
func (widget *Widget) countLines() int {
	return bytes.Count(widget.buffer.Bytes(), []byte{'\n'})
}

// drainLines removed the first n lines from the buffer
func (widget *Widget) drainLines(n int) error {
	for i := 0; i < n; i++ {
		_, err := widget.buffer.ReadBytes('\n')
		if err != nil {
			return err
		}
	}

	return nil
}

func (widget *Widget) environment() []string {
	envs := os.Environ()
	envs = append(
		envs,
		fmt.Sprintf("WTF_WIDGET_WIDTH=%d", widget.settings.width),
		fmt.Sprintf("WTF_WIDGET_HEIGHT=%d", widget.settings.height),
	)
	return envs
}

func runCommandLoop(widget *Widget) {
	// Run the command forever in a loop. Refresh() will put a value into the
	// channel to signal the loop to continue.
	for {
		<-widget.runChan
		widget.resetBuffer()
		cmd := exec.Command(widget.settings.cmd, widget.settings.args...)
		cmd.Stdout = widget
		cmd.Env = widget.environment()
		err := cmd.Run()

		// The command has exited, print any error messages
		if err != nil {
			widget.m.Lock()
			widget.buffer.WriteString(err.Error())
			widget.m.Unlock()
		}
		widget.redrawChan <- true
	}
}

func redrawLoop(widget *Widget) {
	for {
		widget.Redraw(widget.content)
		if widget.settings.tail {
			widget.View.ScrollToEnd()
		}
		<-widget.redrawChan
	}
}

func (widget *Widget) content() (string, string, bool) {
	widget.m.Lock()
	result := widget.buffer.String()
	widget.m.Unlock()

	ansiTitle := tview.TranslateANSI(widget.CommonSettings().Title)
	if ansiTitle == defaultTitle {
		ansiTitle = tview.TranslateANSI(widget.String())
	}
	ansiResult := tview.TranslateANSI(result)

	return ansiTitle, ansiResult, false
}

func (widget *Widget) resetBuffer() {
	widget.m.Lock()
	defer widget.m.Unlock()

	widget.buffer.Reset()
}