Implement directory previews (#842)

* Directory previews, initial implementation.

* Continue previous; add goroutine for directory previews.

* Enable dirpreviews as an option, run gofmt and fix referencing nil.

* Only use dirpreviews if previewer script exists.

* Remove redundant function call to `dirPreview`.

* Remove unnecessary dev-comments.

* Send to `dirPreviewChan` also on modifying folder contents.

app.go

@@ -239,6 +239,7 @@ func (app *app) writeHistory() error {
 // separate goroutines and sent here for update.
 func (app *app) loop() {
 	go app.nav.previewLoop(app.ui)
+	go app.nav.dirPreviewLoop(app.ui)
 
 	var serverChan <-chan expr
 	if !gSingleMode {
@@ -320,6 +321,7 @@ func (app *app) loop() {
 			app.quit()
 
 			app.nav.previewChan <- ""
+			app.nav.dirPreviewChan <- nil
 
 			log.Print("bye!")
 
@@ -384,6 +386,7 @@ func (app *app) loop() {
 			}
 			app.ui.draw(app.nav)
 		case d := <-app.nav.dirChan:
+
 			app.nav.checkDir(d)
 
 			if gOpts.dircache {
@@ -484,6 +487,8 @@ func (app *app) runShell(s string, args []string, prefix string) {
 		cmd.Stderr = os.Stderr
 
 		app.nav.previewChan <- ""
+		app.nav.dirPreviewChan <- nil
+
 		if err := app.ui.suspend(); err != nil {
 			log.Printf("suspend: %s", err)
 		}

complete.go

@@ -123,6 +123,7 @@ var (
 		"nodirfirst",
 		"dirfirst!",
 		"dironly",
+		"dirpreviews",
 		"nodironly",
 		"dironly!",
 		"drawbox",

doc.go

@@ -118,6 +118,7 @@ The following options can be used to customize the behavior of lf:
     dircounts      bool      (default off)
     dirfirst       bool      (default on)
     dironly        bool      (default off)
+    dirpreviews    bool      (default off)
     drawbox        bool      (default off)
     errorfmt       string    (default "\033[7;31;47m%s\033[0m")
     filesep        string    (default "\n")
@@ -597,6 +598,10 @@ Show directories first above regular files.
 
     dironly        bool      (default off)
 
+If enabled, directories will also be passed to the previewer script. This allows custom previews for directories.
+
+    dirpreviews    bool      (default off)
+
 Show only directories.
 
     drawbox        bool      (default off)

eval.go

@@ -44,6 +44,8 @@ func (e *setExpr) eval(app *app, args []string) {
 		app.nav.position()
 		app.ui.sort()
 		app.ui.loadFile(app.nav, true)
+	case "dirpreviews":
+		gOpts.dirpreviews = true
 	case "nodironly":
 		gOpts.dironly = false
 		app.nav.sort()

nav.go

@@ -150,6 +150,7 @@ type dir struct {
 	ignorecase  bool      // ignorecase value from last sort
 	ignoredia   bool      // ignoredia value from last sort
 	noPerm      bool      // whether lf has no permission to open the directory
+	lines       []string  // lines of text to display if directory previews are enabled
 }
 
 func newDir(path string) *dir {
@@ -161,6 +162,7 @@ func newDir(path string) *dir {
 	}
 
 	return &dir{
+		loading:  gOpts.dirpreviews, // Directory is loaded after previewer function exits.
 		loadTime: time,
 		path:     path,
 		files:    files,
@@ -365,6 +367,7 @@ type nav struct {
 	deleteCountChan chan int
 	deleteTotalChan chan int
 	previewChan     chan string
+	dirPreviewChan  chan *dir
 	dirChan         chan *dir
 	regChan         chan *reg
 	dirCache        map[string]*dir
@@ -403,7 +406,11 @@ func (nav *nav) loadDirInternal(path string) *dir {
 		d := newDir(path)
 		d.sort()
 		d.ind, d.pos = 0, 0
+		if gOpts.dirpreviews {
+			nav.dirPreviewChan <- d
+		}
 		nav.dirChan <- d
+
 	}()
 	return d
 }
@@ -447,6 +454,9 @@ func (nav *nav) checkDir(dir *dir) {
 			nd := newDir(dir.path)
 			nd.filter = dir.filter
 			nd.sort()
+			if gOpts.dirpreviews {
+				nav.dirPreviewChan <- nd
+			}
 			nav.dirChan <- nd
 		}()
 	case dir.sortType != gOpts.sortType ||
@@ -490,6 +500,7 @@ func newNav(height int) *nav {
 		deleteCountChan: make(chan int, 1024),
 		deleteTotalChan: make(chan int, 1024),
 		previewChan:     make(chan string, 1024),
+		dirPreviewChan:  make(chan *dir, 1024),
 		dirChan:         make(chan *dir),
 		regChan:         make(chan *reg),
 		dirCache:        make(map[string]*dir),
@@ -599,6 +610,27 @@ func (nav *nav) exportFiles() {
 	exportFiles(currFile, currSelections, nav.currDir().path)
 }
 
+func (nav *nav) dirPreviewLoop(ui *ui) {
+	var prevPath string
+	for {
+		select {
+		case dir := <-nav.dirPreviewChan:
+
+			if dir == nil && len(gOpts.previewer) != 0 && len(gOpts.cleaner) != 0 && nav.volatilePreview {
+				cmd := exec.Command(gOpts.cleaner, prevPath)
+				if err := cmd.Run(); err != nil {
+					log.Printf("cleaning preview: %s", err)
+				}
+				nav.volatilePreview = false
+			} else if dir != nil {
+				win := ui.wins[len(ui.wins)-1]
+				nav.previewDir(dir, win)
+				prevPath = dir.path
+			}
+		}
+	}
+}
+
 func (nav *nav) previewLoop(ui *ui) {
 	var prev string
 	for path := range nav.previewChan {
@@ -648,7 +680,70 @@ func matchPattern(pattern, name, path string) bool {
 	return matched
 }
 
+func (nav *nav) previewDir(dir *dir, win *win) {
+
+	defer func() {
+		dir.loading = false
+		nav.dirChan <- dir
+	}()
+
+	var reader io.Reader
+
+	if len(gOpts.previewer) != 0 {
+		nav.exportFiles()
+		exportOpts()
+		cmd := exec.Command(gOpts.previewer, dir.path,
+			strconv.Itoa(win.w),
+			strconv.Itoa(win.h),
+			strconv.Itoa(win.x),
+			strconv.Itoa(win.y))
+
+		out, err := cmd.StdoutPipe()
+		if err != nil {
+			log.Printf("previewing dir: %s", err)
+			return
+		}
+
+		if err := cmd.Start(); err != nil {
+			log.Printf("previewing dir: %s", err)
+			out.Close()
+			return
+		}
+
+		defer func() {
+			if err := cmd.Wait(); err != nil {
+				if e, ok := err.(*exec.ExitError); ok {
+					if e.ExitCode() != 0 {
+						nav.volatilePreview = true
+					}
+				} else {
+					log.Printf("loading dir: %s", err)
+				}
+			}
+		}()
+		defer out.Close()
+		reader = out
+		buf := bufio.NewScanner(reader)
+
+		for i := 0; i < win.h && buf.Scan(); i++ {
+			for _, r := range buf.Text() {
+				if r == 0 {
+					dir.lines = []string{"\033[7mbinary\033[0m"}
+					return
+				}
+			}
+			dir.lines = append(dir.lines, buf.Text())
+		}
+
+		if buf.Err() != nil {
+			log.Printf("loading dir: %s", buf.Err())
+		}
+	}
+
+}
+
 func (nav *nav) preview(path string, win *win) {
+
 	reg := &reg{loadTime: time.Now(), path: path}
 	defer func() { nav.regChan <- reg }()
 

opts.go

@@ -33,6 +33,7 @@ var gOpts struct {
 	dircache       bool
 	dircounts      bool
 	dironly        bool
+	dirpreviews    bool
 	drawbox        bool
 	globsearch     bool
 	icons          bool
@@ -84,6 +85,7 @@ func init() {
 	gOpts.dircache = true
 	gOpts.dircounts = false
 	gOpts.dironly = false
+	gOpts.dirpreviews = false
 	gOpts.drawbox = false
 	gOpts.globsearch = false
 	gOpts.icons = false

ui.go

@@ -324,7 +324,8 @@ func fileInfo(f *file, d *dir) string {
 	return info
 }
 
-func (win *win) printDir(screen tcell.Screen, dir *dir, selections map[string]int, saves map[string]bool, tags map[string]string, colors styleMap, icons iconMap) {
+func (win *win) printDir(screen tcell.Screen, dir *dir, selections map[string]int, saves map[string]bool, tags map[string]string, colors styleMap, icons iconMap, previewAllowed bool) {
+
 	if win.w < 5 || dir == nil {
 		return
 	}
@@ -334,11 +335,25 @@ func (win *win) printDir(screen tcell.Screen, dir *dir, selections map[string]in
 		return
 	}
 
-	if dir.loading && len(dir.files) == 0 {
+	if (dir.loading && len(dir.files) == 0) || (previewAllowed && dir.loading && gOpts.dirpreviews) {
 		win.print(screen, 2, 0, tcell.StyleDefault.Reverse(true), "loading...")
 		return
 	}
 
+	if previewAllowed && gOpts.dirpreviews && len(gOpts.previewer) > 0 {
+
+		// Print previewer result instead of default directory print operation.
+		st := tcell.StyleDefault
+		for i, l := range dir.lines {
+			if i > win.h-1 {
+				break
+			}
+
+			st = win.print(screen, 2, i, st, l)
+		}
+		return
+	}
+
 	if len(dir.files) == 0 {
 		win.print(screen, 2, 0, tcell.StyleDefault.Reverse(true), "empty")
 		return
@@ -855,7 +870,7 @@ func (ui *ui) draw(nav *nav) {
 
 	doff := len(nav.dirs) - length
 	for i := 0; i < length; i++ {
-		ui.wins[woff+i].printDir(ui.screen, nav.dirs[doff+i], nav.selections, nav.saves, nav.tags, ui.styles, ui.icons)
+		ui.wins[woff+i].printDir(ui.screen, nav.dirs[doff+i], nav.selections, nav.saves, nav.tags, ui.styles, ui.icons, false)
 	}
 
 	switch ui.cmdPrefix {
@@ -889,7 +904,7 @@ func (ui *ui) draw(nav *nav) {
 			preview := ui.wins[len(ui.wins)-1]
 
 			if curr.IsDir() {
-				preview.printDir(ui.screen, ui.dirPrev, nav.selections, nav.saves, nav.tags, ui.styles, ui.icons)
+				preview.printDir(ui.screen, ui.dirPrev, nav.selections, nav.saves, nav.tags, ui.styles, ui.icons, true)
 			} else if curr.Mode().IsRegular() {
 				preview.printReg(ui.screen, ui.regPrev)
 			}