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
@@ -444,6 +445,7 @@ func newUI() *ui {
 		pwdWin:   newWin(wtot, 1, 0, 0),
 		msgWin:   newWin(wtot, 1, 0, htot-1),
 		menuWin:  newWin(wtot, 1, 0, htot-2),
+		prevChan: make(chan preview),
 		keyChan:  make(chan string, 1000),
 		evChan:   evChan,
 	}
@@ -473,20 +475,17 @@ func (ui *ui) printf(format string, a ...interface{}) {
 	ui.print(fmt.Sprintf(format, a...))
 }
 
-func (ui *ui) loadFile(nav *nav) {
+type preview struct {
+	path  string
+	lines []string
+}
+
+func (ui *ui) preview(nav *nav) {
 	curr, err := nav.currFile()
 	if err != nil {
 		return
 	}
 
-	if !gOpts.preview {
-		return
-	}
-
-	if curr.IsDir() {
-		dir := nav.load(curr.path)
-		ui.dirPrev = dir
-	} else if curr.Mode().IsRegular() {
 	var reader io.Reader
 
 	if len(gOpts.previewer) != 0 {
@@ -514,23 +513,45 @@ func (ui *ui) loadFile(nav *nav) {
 		reader = f
 	}
 
-		ui.regPrev = nil
+	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 {
-					ui.regPrev = []string{"\033[1mbinary\033[0m"}
+				prev.lines = []string{"\033[1mbinary\033[0m"}
+				ui.prevChan <- prev
 				return
 			}
 		}
-			ui.regPrev = append(ui.regPrev, buf.Text())
+		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 {
+		return
+	}
+
+	if !gOpts.preview {
+		return
+	}
+
+	if curr.IsDir() {
+		ui.dirPrev = nav.load(curr.path)
+	} else if curr.Mode().IsRegular() {
+		ui.regPrev = []string{"\033[1mloading...\033[0m"}
+		go ui.preview(nav)
 	}
 }