From 9991a40e87ff74b7a21fcaeda0414593a4627093 Mon Sep 17 00:00:00 2001
From: Kennedy Mwenja <kmwenja@users.noreply.github.com>
Date: Fri, 4 Oct 2019 21:44:52 +0300
Subject: [PATCH] Sort by file extensions (#230)

- preserve natural ordering of filenames if extensions are the same
  or are missing
- files without extensions rank higher on ascending sort and lower
  on descending sort
---
 docstring.go |  1 +
 eval.go      |  4 +++-
 nav.go       | 26 ++++++++++++++++++++++++++
 opts.go      |  2 ++
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/docstring.go b/docstring.go
index 2132b35..438b31f 100644
--- a/docstring.go
+++ b/docstring.go
@@ -179,6 +179,7 @@ The following additional keybindings are provided by default:
     map st :set sortby time; set info time
     map sa :set sortby atime; set info atime
     map sc :set sortby ctime; set info ctime
+	map se :set sortby ext; set info
     map gh cd ~
 
 The following keybindings to applications are provided by default:
diff --git a/eval.go b/eval.go
index 9f4a5eb..2d0ade2 100644
--- a/eval.go
+++ b/eval.go
@@ -251,8 +251,10 @@ func (e *setExpr) eval(app *app, args []string) {
 			gOpts.sortType.method = ctimeSort
 		case "atime":
 			gOpts.sortType.method = atimeSort
+		case "ext":
+			gOpts.sortType.method = extSort
 		default:
-			app.ui.echoerr("sortby: value should either be 'natural', 'name', 'size', 'time', 'atime' or 'ctime'")
+			app.ui.echoerr("sortby: value should either be 'natural', 'name', 'size', 'time', 'atime', 'ctime' or 'ext'")
 			return
 		}
 		app.nav.sort()
diff --git a/nav.go b/nav.go
index 7b369c5..1921387 100644
--- a/nav.go
+++ b/nav.go
@@ -32,6 +32,7 @@ type file struct {
 	dirCount   int
 	accessTime time.Time
 	changeTime time.Time
+	ext        string
 }
 
 func readdir(path string) ([]*file, error) {
@@ -77,6 +78,10 @@ func readdir(path string) ([]*file, error) {
 			ct = lstat.ModTime()
 		}
 
+		// returns an empty string if extension could not be determined
+		// i.e. directories, filenames without extensions
+		ext := filepath.Ext(fpath)
+
 		files = append(files, &file{
 			FileInfo:   lstat,
 			linkState:  linkState,
@@ -84,6 +89,7 @@ func readdir(path string) ([]*file, error) {
 			dirCount:   -1,
 			accessTime: at,
 			changeTime: ct,
+			ext:        ext,
 		})
 	}
 
@@ -149,6 +155,26 @@ func (dir *dir) sort() {
 		sort.SliceStable(dir.files, func(i, j int) bool {
 			return dir.files[i].changeTime.Before(dir.files[j].changeTime)
 		})
+	case extSort:
+		sort.SliceStable(dir.files, func(i, j int) bool {
+			leftExt := strings.ToLower(dir.files[i].ext)
+			rightExt := strings.ToLower(dir.files[j].ext)
+
+			// if the extension could not be determined (directories, files without)
+			// use a zero byte so that these files can be ranked higher
+			if leftExt == "" {
+				leftExt = "\x00"
+			}
+			if rightExt == "" {
+				rightExt = "\x00"
+			}
+
+			// in order to also have natural sorting with the filenames
+			// combine the name with the ext but have the ext at the front
+			left := leftExt + strings.ToLower(dir.files[i].Name())
+			right := rightExt + strings.ToLower(dir.files[j].Name())
+			return left < right
+		})
 	}
 
 	if gOpts.sortType.option&reverseSort != 0 {
diff --git a/opts.go b/opts.go
index aef8c06..25cdc1c 100644
--- a/opts.go
+++ b/opts.go
@@ -11,6 +11,7 @@ const (
 	timeSort
 	atimeSort
 	ctimeSort
+	extSort
 )
 
 type sortOption byte
@@ -157,6 +158,7 @@ func init() {
 	gOpts.keys["st"] = &listExpr{[]expr{&setExpr{"sortby", "time"}, &setExpr{"info", "time"}}}
 	gOpts.keys["sa"] = &listExpr{[]expr{&setExpr{"sortby", "atime"}, &setExpr{"info", "atime"}}}
 	gOpts.keys["sc"] = &listExpr{[]expr{&setExpr{"sortby", "ctime"}, &setExpr{"info", "ctime"}}}
+	gOpts.keys["se"] = &listExpr{[]expr{&setExpr{"sortby", "ext"}, &setExpr{"info", ""}}}
 	gOpts.keys["gh"] = &callExpr{"cd", []string{"~"}, 1}
 
 	gOpts.cmdkeys = make(map[string]expr)