From bc724bf781ef8cb225003b390ce07ea3857312dd Mon Sep 17 00:00:00 2001
From: boombuler <boombuler@gmail.com>
Date: Wed, 28 Sep 2016 21:54:34 +0200
Subject: [PATCH] fixes #379 (second try)

---
 cmd/micro/util.go      | 22 ++++++++++++++++++++--
 cmd/micro/util_test.go | 38 ++++++++++++++++++++++++++++++++++++++
 cmd/micro/view.go      |  4 +++-
 3 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/cmd/micro/util.go b/cmd/micro/util.go
index 4402a22e..1577866d 100644
--- a/cmd/micro/util.go
+++ b/cmd/micro/util.go
@@ -157,7 +157,19 @@ func GetModTime(path string) (time.Time, bool) {
 // StringWidth returns the width of a string where tabs count as `tabsize` width
 func StringWidth(str string, tabsize int) int {
 	sw := runewidth.StringWidth(str)
-	sw += NumOccurrences(str, '\t') * (tabsize - 1)
+	lineIdx := 0
+	for _, ch := range str {
+		switch ch {
+		case '\t':
+			ts := tabsize - (lineIdx % tabsize)
+			sw += ts - 1
+			lineIdx += ts
+		case '\n':
+			lineIdx = 0
+		default:
+			lineIdx++
+		}
+	}
 	return sw
 }
 
@@ -165,16 +177,22 @@ func StringWidth(str string, tabsize int) int {
 // that have a width larger than 1 (this also counts tabs as `tabsize` width)
 func WidthOfLargeRunes(str string, tabsize int) int {
 	count := 0
+	lineIdx := 0
 	for _, ch := range str {
 		var w int
 		if ch == '\t' {
-			w = tabsize
+			w = tabsize - (lineIdx % tabsize)
 		} else {
 			w = runewidth.RuneWidth(ch)
 		}
 		if w > 1 {
 			count += (w - 1)
 		}
+		if ch == '\n' {
+			lineIdx = 0
+		} else {
+			lineIdx += w
+		}
 	}
 	return count
 }
diff --git a/cmd/micro/util_test.go b/cmd/micro/util_test.go
index 16e46fe4..0104218e 100644
--- a/cmd/micro/util_test.go
+++ b/cmd/micro/util_test.go
@@ -116,3 +116,41 @@ func TestJoinAndSplitCommandArgs(t *testing.T) {
 		}
 	}
 }
+
+func TestStringWidth(t *testing.T) {
+	tabsize := 4
+	if w := StringWidth("1\t2", tabsize); w != 5 {
+		t.Error("StringWidth 1 Failed. Got", w)
+	}
+	if w := StringWidth("\t", tabsize); w != 4 {
+		t.Error("StringWidth 2 Failed. Got", w)
+	}
+	if w := StringWidth("1\t", tabsize); w != 4 {
+		t.Error("StringWidth 3 Failed. Got", w)
+	}
+	if w := StringWidth("\t\t", tabsize); w != 8 {
+		t.Error("StringWidth 4 Failed. Got", w)
+	}
+	if w := StringWidth("12\t2\t", tabsize); w != 8 {
+		t.Error("StringWidth 5 Failed. Got", w)
+	}
+}
+
+func TestWidthOfLargeRunes(t *testing.T) {
+	tabsize := 4
+	if w := WidthOfLargeRunes("1\t2", tabsize); w != 2 {
+		t.Error("WidthOfLargeRunes 1 Failed. Got", w)
+	}
+	if w := WidthOfLargeRunes("\t", tabsize); w != 3 {
+		t.Error("WidthOfLargeRunes 2 Failed. Got", w)
+	}
+	if w := WidthOfLargeRunes("1\t", tabsize); w != 2 {
+		t.Error("WidthOfLargeRunes 3 Failed. Got", w)
+	}
+	if w := WidthOfLargeRunes("\t\t", tabsize); w != 6 {
+		t.Error("WidthOfLargeRunes 4 Failed. Got", w)
+	}
+	if w := WidthOfLargeRunes("12\t2\t", tabsize); w != 3 {
+		t.Error("WidthOfLargeRunes 5 Failed. Got", w)
+	}
+}
diff --git a/cmd/micro/view.go b/cmd/micro/view.go
index aef1ccea..43b38f25 100644
--- a/cmd/micro/view.go
+++ b/cmd/micro/view.go
@@ -777,7 +777,9 @@ func (v *View) DisplayView() {
 				}
 				// Now the tab has to be displayed as a bunch of spaces
 				tabSize := int(v.Buf.Settings["tabsize"].(float64))
-				for i := 0; i < tabSize-1; i++ {
+				visLoc := StringWidth(line[:colN], tabSize)
+				remainder := tabSize - (visLoc % tabSize)
+				for i := 0; i < remainder-1; i++ {
 					screenX++
 					if screenX-v.x-v.leftCol >= v.lineNumOffset {
 						v.drawCell(screenX-v.leftCol, screenY, ' ', nil, lineStyle)