From d7028cee00b06e81086732aaa47dfdd7cf4c3a45 Mon Sep 17 00:00:00 2001
From: Achilleas Anagnostopoulos <achilleas.imap.mbox@gmail.com>
Date: Fri, 12 May 2017 07:54:42 +0100
Subject: [PATCH] Make TTYs implement io.ByteWriter and add support for TAB/BS
 chars

---
 kernel/driver/tty/tty.go     |  1 +
 kernel/driver/tty/vt.go      | 50 ++++++++++++++++++++++++++----------
 kernel/driver/tty/vt_test.go | 22 ++++++++++++++--
 3 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/kernel/driver/tty/tty.go b/kernel/driver/tty/tty.go
index 2f74a7c..f46ce2f 100644
--- a/kernel/driver/tty/tty.go
+++ b/kernel/driver/tty/tty.go
@@ -5,6 +5,7 @@ import "io"
 // Tty is implemented by objects that can register themselves as ttys.
 type Tty interface {
 	io.Writer
+	io.ByteWriter
 
 	// Position returns the current cursor position (x, y).
 	Position() (uint16, uint16)
diff --git a/kernel/driver/tty/vt.go b/kernel/driver/tty/vt.go
index 8ecd2a5..d831bc1 100644
--- a/kernel/driver/tty/vt.go
+++ b/kernel/driver/tty/vt.go
@@ -5,6 +5,7 @@ import "github.com/achilleasa/gopher-os/kernel/driver/video/console"
 const (
 	defaultFg = console.LightGrey
 	defaultBg = console.Black
+	tabWidth  = 4
 )
 
 // Vt implements a simple terminal that can process LF and CR characters. The
@@ -59,26 +60,47 @@ func (t *Vt) SetPosition(x, y uint16) {
 
 // Write implements io.Writer.
 func (t *Vt) Write(data []byte) (int, error) {
-	attr := t.curAttr
 	for _, b := range data {
-		switch b {
-		case '\r':
-			t.cr()
-		case '\n':
-			t.cr()
-			t.lf()
-		default:
-			t.cons.Write(b, attr, t.curX, t.curY)
-			t.curX++
-			if t.curX == t.width {
-				t.lf()
-			}
-		}
+		t.WriteByte(b)
 	}
 
 	return len(data), nil
 }
 
+// Write implements io.ByteWriter.
+func (t *Vt) WriteByte(b byte) error {
+	switch b {
+	case '\r':
+		t.cr()
+	case '\n':
+		t.cr()
+		t.lf()
+	case '\b':
+		if t.curX > 0 {
+			t.cons.Write(' ', t.curAttr, t.curX, t.curY)
+			t.curX--
+		}
+	case '\t':
+		for i := 0; i < tabWidth; i++ {
+			t.cons.Write(' ', t.curAttr, t.curX, t.curY)
+			t.curX++
+			if t.curX == t.width {
+				t.cr()
+				t.lf()
+			}
+		}
+	default:
+		t.cons.Write(b, t.curAttr, t.curX, t.curY)
+		t.curX++
+		if t.curX == t.width {
+			t.cr()
+			t.lf()
+		}
+	}
+
+	return nil
+}
+
 // cls clears the terminal.
 func (t *Vt) clear() {
 	t.cons.Clear(0, 0, t.width, t.height)
diff --git a/kernel/driver/tty/vt_test.go b/kernel/driver/tty/vt_test.go
index 19233b0..844a81f 100644
--- a/kernel/driver/tty/vt_test.go
+++ b/kernel/driver/tty/vt_test.go
@@ -44,7 +44,12 @@ func TestWrite(t *testing.T) {
 
 	vt.Clear()
 	vt.SetPosition(0, 1)
-	vt.Write([]byte("12\n3\n4\r56"))
+	vt.Write([]byte("12\n\t3\n4\r567\b8"))
+
+	// Tab spanning rows
+	vt.SetPosition(78, 4)
+	vt.WriteByte('\t')
+	vt.WriteByte('9')
 
 	// Trigger scroll
 	vt.SetPosition(79, 24)
@@ -56,9 +61,22 @@ func TestWrite(t *testing.T) {
 	}{
 		{0, 0, '1'},
 		{1, 0, '2'},
-		{0, 1, '3'},
+		// tabs
+		{0, 1, ' '},
+		{1, 1, ' '},
+		{2, 1, ' '},
+		{3, 1, ' '},
+		{4, 1, '3'},
+		// tab spanning 2 rows
+		{78, 3, ' '},
+		{79, 3, ' '},
+		{0, 4, ' '},
+		{1, 4, ' '},
+		{2, 4, '9'},
+		//
 		{0, 2, '5'},
 		{1, 2, '6'},
+		{2, 2, '8'}, // overwritten by BS
 		{79, 23, '!'},
 	}