Flexible filename truncation

complete.go

@@ -218,6 +218,7 @@ var (
 		"infotimefmtnew",
 		"infotimefmtold",
 		"truncatechar",
+		"truncatepct",
 	}
 )
 

doc.go

@@ -172,6 +172,7 @@ The following options can be used to customize the behavior of lf:
 	tempmarks        string    (default '')
 	timefmt          string    (default 'Mon Jan _2 15:04:05 2006')
 	truncatechar     string    (default '~')
+	truncatepct      int       (default 100)
 	waitmsg          string    (default 'Press any key to continue')
 	wrapscan         bool      (default true)
 	wrapscroll       bool      (default false)
@@ -941,6 +942,25 @@ Format string of the file modification time shown in the bottom line.
 
 Truncate character shown at the end when the file name does not fit to the pane.
 
+	truncatepct  int       (default 100)
+
+When a filename is too long to be shown completely, the available space is
+partitioned in two pieces. truncatepct defines a fraction (in percent
+between 0 and 100) for the size of the first piece, which will show the
+beginning of the filename. The second piece will show the end of the filename
+and will use the rest of the available space. Both pieces are separated by the
+truncation character (truncatechar).
+A value of 100 will only show the beginning of the filename,
+while a value of 0 will only show the end of the filename, e.g.:
+
+  - `set truncatepct 100` -> "very-long-filename-tr~" (default)
+
+  - `set truncatepct 50`  -> "very-long-f~-truncated"
+
+  - `set truncatepct 0`   -> "~ng-filename-truncated"
+
+.
+
 	waitmsg        string    (default 'Press any key to continue')
 
 String shown after commands of shell-wait type.

eval.go

@@ -831,6 +831,17 @@ func (e *setExpr) eval(app *app, args []string) {
 		}
 
 		gOpts.truncatechar = e.val
+	case "truncatepct":
+		n, err := strconv.Atoi(e.val)
+		if err != nil {
+			app.ui.echoerrf("truncatepct: %s", err)
+			return
+		}
+		if n < 0 || n > 100 {
+			app.ui.echoerrf("truncatepct: must be between 0 and 100 (both inclusive), got %d", n)
+			return
+		}
+		gOpts.truncatepct = n
 	case "waitmsg":
 		gOpts.waitmsg = e.val
 	case "wrapscan":

lf.1

@@ -191,6 +191,7 @@ The following options can be used to customize the behavior of lf:
     tempmarks        string    (default '')
     timefmt          string    (default 'Mon Jan _2 15:04:05 2006')
     truncatechar     string    (default '~')
+    truncatepct      int       (default 100)
     waitmsg          string    (default 'Press any key to continue')
     wrapscan         bool      (default true)
     wrapscroll       bool      (default false)
@@ -1119,6 +1120,26 @@ Format string of the file modification time shown in the bottom line.
 .PP
 Truncate character shown at the end when the file name does not fit to the pane.
 .PP
+.EX
+    truncatepct  int       (default 100)
+.EE
+.PP
+When a filename is too long to be shown completely, the available space is partitioned in two pieces. truncatepct defines a fraction (in percent between 0 and 100) for the size of the first piece, which will show the beginning of the filename. The second piece will show the end of the filename and will use the rest of the available space. Both pieces are separated by the truncation character (truncatechar). A value of 100 will only show the beginning of the filename, while a value of 0 will only show the end of the filename, e.g.:
+.PP
+.EX
+  - `set truncatepct 100` -> "very-long-filename-tr~" (default)
+.EE
+.PP
+.EX
+  - `set truncatepct 50` -> "very-long-f~-truncated"
+.EE
+.PP
+.EX
+  - `set truncatepct 0` -> "~ng-filename-truncated"
+.EE
+.PP
+.
+.PP
 .EX
     waitmsg        string    (default 'Press any key to continue')
 .EE

misc.go

@@ -53,6 +53,19 @@ func runeSliceWidthRange(rs []rune, beg, end int) []rune {
 	return rs[b:]
 }
 
+// Returns the last runes of `rs` that take up at most `maxWidth` space.
+func runeSliceWidthLastRange(rs []rune, maxWidth int) []rune {
+	lastWidth := 0
+	for i := len(rs) - 1; i >= 0; i-- {
+		w := runewidth.RuneWidth(rs[i])
+		if lastWidth+w > maxWidth {
+			return rs[i+1:]
+		}
+		lastWidth += w
+	}
+	return rs
+}
+
 // This function is used to escape whitespaces and special characters with
 // backlashes in a given string.
 func escape(s string) string {

misc_test.go

@@ -83,6 +83,47 @@ func TestRuneSliceWidthRange(t *testing.T) {
 	}
 }
 
+func TestRuneSliceWidthLastRange(t *testing.T) {
+	tests := []struct {
+		rs       []rune
+		maxWidth int
+		exp      []rune
+	}{
+		{[]rune{}, 0, []rune{}},
+		{[]rune{}, 1, []rune{}},
+		{[]rune{'a', 'ı', 'b', ' '}, 0, []rune{}},
+		{[]rune{'a', 'ı', 'b', ' '}, 1, []rune{' '}},
+		{[]rune{'a', 'ı', 'b', ' '}, 2, []rune{'b', ' '}},
+		{[]rune{'a', 'ı', 'b', ' '}, 3, []rune{'ı', 'b', ' '}},
+		{[]rune{'a', 'ı', 'b', ' '}, 4, []rune{'a', 'ı', 'b', ' '}},
+		{[]rune{'a', 'ı', 'b', ' '}, 5, []rune{'a', 'ı', 'b', ' '}},
+		{[]rune{'世', '界', '世', '界'}, 0, []rune{}},
+		{[]rune{'世', '界', '世', '界'}, 1, []rune{}},
+		{[]rune{'世', '界', '世', '界'}, 2, []rune{'界'}},
+		{[]rune{'世', '界', '世', '界'}, 3, []rune{'界'}},
+		{[]rune{'世', '界', '世', '界'}, 4, []rune{'世', '界'}},
+		{[]rune{'世', '界', '世', '界'}, 5, []rune{'世', '界'}},
+		{[]rune{'世', '界', '世', '界'}, 6, []rune{'界', '世', '界'}},
+		{[]rune{'世', '界', '世', '界'}, 7, []rune{'界', '世', '界'}},
+		{[]rune{'世', '界', '世', '界'}, 8, []rune{'世', '界', '世', '界'}},
+		{[]rune{'世', '界', '世', '界'}, 9, []rune{'世', '界', '世', '界'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 0, []rune{}},
+		{[]rune{'世', 'a', '界', 'ı'}, 1, []rune{'ı'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 2, []rune{'ı'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 3, []rune{'界', 'ı'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 4, []rune{'a', '界', 'ı'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 5, []rune{'a', '界', 'ı'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 6, []rune{'世', 'a', '界', 'ı'}},
+		{[]rune{'世', 'a', '界', 'ı'}, 7, []rune{'世', 'a', '界', 'ı'}},
+	}
+
+	for _, test := range tests {
+		if got := runeSliceWidthLastRange(test.rs, test.maxWidth); !reflect.DeepEqual(got, test.exp) {
+			t.Errorf("at input '%v' expected '%v' but got '%v'", test.rs, test.exp, got)
+		}
+	}
+}
+
 func TestEscape(t *testing.T) {
 	tests := []struct {
 		s   string

opts.go

@@ -72,6 +72,7 @@ var gOpts struct {
 	infotimefmtnew   string
 	infotimefmtold   string
 	truncatechar     string
+	truncatepct      int
 	ratios           []int
 	hiddenfiles      []string
 	history          bool
@@ -133,6 +134,7 @@ func init() {
 	gOpts.infotimefmtnew = "Jan _2 15:04"
 	gOpts.infotimefmtold = "Jan _2  2006"
 	gOpts.truncatechar = "~"
+	gOpts.truncatepct = 100
 	gOpts.ratios = []int{1, 2, 3}
 	gOpts.hiddenfiles = []string{".*"}
 	gOpts.history = true

ui.go

@@ -468,8 +468,11 @@ func (win *win) printDir(screen tcell.Screen, dir *dir, context *dirContext, dir
 
 		filename := []rune(f.Name())
 		if runeSliceWidth(filename) > maxFilenameWidth {
-			filename = runeSliceWidthRange(filename, 0, maxFilenameWidth-1)
+			truncatePos := (maxFilenameWidth - 1) * gOpts.truncatepct / 100
+			lastPart := runeSliceWidthLastRange(filename, maxFilenameWidth-truncatePos-1)
+			filename = runeSliceWidthRange(filename, 0, truncatePos)
 			filename = append(filename, []rune(gOpts.truncatechar)...)
+			filename = append(filename, lastPart...)
 		}
 		for i := runeSliceWidth(filename); i < maxFilenameWidth; i++ {
 			filename = append(filename, ' ')