preview files asynchronously

Mentioned in #5 and #92.

app.go

@@ -106,6 +106,15 @@ func (app *app) loop() {
 				}
 			}
 
+			app.ui.draw(app.nav)
+		case p := <-app.ui.prevChan:
+			curr, err := app.nav.currFile()
+			if err == nil {
+				if p.path == curr.path {
+					app.ui.regPrev = p.lines
+				}
+			}
+
 			app.ui.draw(app.nav)
 		case e := <-clientChan:
 			for i := 0; i < e.count; i++ {

ui.go

@@ -381,6 +381,7 @@ type ui struct {
 	msg         string
 	regPrev     []string
 	dirPrev     *dir
+	prevChan    chan preview
 	keyChan     chan string
 	evChan      chan termbox.Event
 	menuBuf     *bytes.Buffer
@@ -440,12 +441,13 @@ func newUI() *ui {
 	}()
 
 	return &ui{
-		wins:    getWins(),
+		wins:     getWins(),
-		pwdWin:  newWin(wtot, 1, 0, 0),
+		pwdWin:   newWin(wtot, 1, 0, 0),
-		msgWin:  newWin(wtot, 1, 0, htot-1),
+		msgWin:   newWin(wtot, 1, 0, htot-1),
-		menuWin: newWin(wtot, 1, 0, htot-2),
+		menuWin:  newWin(wtot, 1, 0, htot-2),
-		keyChan: make(chan string, 1000),
+		prevChan: make(chan preview),
-		evChan:  evChan,
+		keyChan:  make(chan string, 1000),
+		evChan:   evChan,
 	}
 }
 
@@ -473,6 +475,68 @@ func (ui *ui) printf(format string, a ...interface{}) {
 	ui.print(fmt.Sprintf(format, a...))
 }
 
+type preview struct {
+	path  string
+	lines []string
+}
+
+func (ui *ui) preview(nav *nav) {
+	curr, err := nav.currFile()
+	if err != nil {
+		return
+	}
+
+	var reader io.Reader
+
+	if len(gOpts.previewer) != 0 {
+		cmd := exec.Command(gOpts.previewer, curr.path, strconv.Itoa(nav.height))
+
+		out, err := cmd.StdoutPipe()
+		if err != nil {
+			ui.printf("previewing file: %s", err)
+		}
+
+		if err := cmd.Start(); err != nil {
+			ui.printf("previewing file: %s", err)
+		}
+
+		defer cmd.Wait()
+		defer out.Close()
+		reader = out
+	} else {
+		f, err := os.Open(curr.path)
+		if err != nil {
+			ui.printf("opening file: %s", err)
+		}
+
+		defer f.Close()
+		reader = f
+	}
+
+	var prev preview
+
+	prev.path = curr.path
+
+	buf := bufio.NewScanner(reader)
+
+	for i := 0; i < nav.height && buf.Scan(); i++ {
+		for _, r := range buf.Text() {
+			if r == 0 {
+				prev.lines = []string{"\033[1mbinary\033[0m"}
+				ui.prevChan <- prev
+				return
+			}
+		}
+		prev.lines = append(prev.lines, buf.Text())
+	}
+
+	if buf.Err() != nil {
+		ui.printf("loading file: %s", buf.Err())
+	}
+
+	ui.prevChan <- prev
+}
+
 func (ui *ui) loadFile(nav *nav) {
 	curr, err := nav.currFile()
 	if err != nil {
@@ -484,53 +548,10 @@ func (ui *ui) loadFile(nav *nav) {
 	}
 
 	if curr.IsDir() {
-		dir := nav.load(curr.path)
+		ui.dirPrev = nav.load(curr.path)
-		ui.dirPrev = dir
 	} else if curr.Mode().IsRegular() {
-		var reader io.Reader
+		ui.regPrev = []string{"\033[1mloading...\033[0m"}
-
+		go ui.preview(nav)
-		if len(gOpts.previewer) != 0 {
-			cmd := exec.Command(gOpts.previewer, curr.path, strconv.Itoa(nav.height))
-
-			out, err := cmd.StdoutPipe()
-			if err != nil {
-				ui.printf("previewing file: %s", err)
-			}
-
-			if err := cmd.Start(); err != nil {
-				ui.printf("previewing file: %s", err)
-			}
-
-			defer cmd.Wait()
-			defer out.Close()
-			reader = out
-		} else {
-			f, err := os.Open(curr.path)
-			if err != nil {
-				ui.printf("opening file: %s", err)
-			}
-
-			defer f.Close()
-			reader = f
-		}
-
-		ui.regPrev = nil
-
-		buf := bufio.NewScanner(reader)
-
-		for i := 0; i < nav.height && buf.Scan(); i++ {
-			for _, r := range buf.Text() {
-				if r == 0 {
-					ui.regPrev = []string{"\033[1mbinary\033[0m"}
-					return
-				}
-			}
-			ui.regPrev = append(ui.regPrev, buf.Text())
-		}
-
-		if buf.Err() != nil {
-			ui.printf("loading file: %s", buf.Err())
-		}
 	}
 }