From ae65be003c2f8f423f917d4211eff423967a7f4e Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Wed, 31 Mar 2021 14:32:43 -0400
Subject: [PATCH] Fix some offset errors for cursor operations

---
 editor/constants.go |  3 ++-
 editor/draw.go      |  7 ++++---
 editor/editor.go    | 31 +++++++++++++++++++++----------
 editor/row.go       | 24 +++++++++++++++++++++---
 editor/row_test.go  |  6 +++---
 5 files changed, 51 insertions(+), 20 deletions(-)

diff --git a/editor/constants.go b/editor/constants.go
index 2b40751..2819ccc 100644
--- a/editor/constants.go
+++ b/editor/constants.go
@@ -4,4 +4,5 @@ package editor
 // !Constants
 // ----------------------------------------------------------------------------
 
-const KiloVersion = "0.0.1"
\ No newline at end of file
+const KiloVersion = "0.0.1"
+const KiloTabStop = 4
\ No newline at end of file
diff --git a/editor/draw.go b/editor/draw.go
index 0946e73..ea57c3e 100644
--- a/editor/draw.go
+++ b/editor/draw.go
@@ -56,14 +56,15 @@ func (e *editor) drawRows(ab *buffer) {
 
 			// If the column offset is greater than the length of the row,
 			// just display an empty row
-			if e.offset.x > rawRow.Size() {
+			if e.offset.x > rawRow.size() {
 				ab.append("")
 
 				continue
 			}
 
-			row := truncateString(string(e.rows[fileRow].chars[e.offset.x:]), e.screen.Cols)
-			ab.append(row)
+			rowLen := e.rows[fileRow].rSize() - e.offset.x
+			outputRow := truncateString(string(e.rows[fileRow].render[e.offset.x:]), rowLen)
+			ab.append(outputRow)
 		}
 
 		ab.append(terminal.ClearLine)
diff --git a/editor/editor.go b/editor/editor.go
index 7188508..58771cd 100644
--- a/editor/editor.go
+++ b/editor/editor.go
@@ -86,7 +86,7 @@ func (e *editor) ProcessKeypress() bool {
 
 func (e *editor) moveCursor (key string) {
 	var row *row
-	if e.cursor.y > len(e.rows) {
+	if e.cursor.y >= len(e.rows) {
 		row = nil
 	} else {
 		row = e.rows[e.cursor.y]
@@ -101,15 +101,15 @@ func (e *editor) moveCursor (key string) {
 		// Move from beginning of current row to end of previous row
 		if e.cursor.y > 0 {
 			e.cursor.y -= 1
-			e.cursor.x = e.rows[e.cursor.y].Size()
+			e.cursor.x = e.rows[e.cursor.y].size()
 		}
 	case keyRight:
-		if row != nil && e.cursor.x < row.Size() {
+		if row != nil && e.cursor.x < row.size() {
 			e.cursor.x += 1
 		}
 
 		// Move from end of current line to beginning of next line
-		if row != nil && e.cursor.x == row.Size() {
+		if row != nil && e.cursor.x == row.size() && e.cursor.y < len(e.rows) - 1 {
 			e.cursor.y += 1
 			e.cursor.x = 0
 		}
@@ -118,18 +118,28 @@ func (e *editor) moveCursor (key string) {
 			e.cursor.y -= 1
 		}
 	case keyDown:
-		if e.cursor.y < len(e.rows) {
+		if e.cursor.y < (len(e.rows) - 1) {
 			e.cursor.y += 1
 		}
 	case keyPageUp:
-		e.cursor.y = 0
+		if e.cursor.y > e.screen.Rows {
+			e.cursor.y -= e.screen.Rows
+		} else {
+			e.cursor.y = 0
+		}
+
 	case keyPageDown:
-		e.cursor.y = e.screen.Rows
+		if e.cursor.y + e.screen.Rows > len(e.rows) {
+			e.cursor.y += e.screen.Rows
+		} else {
+			e.cursor.y = len(e.rows) - 1
+		}
+
 	case keyHome:
 		e.cursor.x = 0
 	case keyEnd:
 		if row != nil {
-			e.cursor.x = row.Size()
+			e.cursor.x = row.size()
 		}
 	}
 
@@ -137,7 +147,7 @@ func (e *editor) moveCursor (key string) {
 		row = nil
 	} else {
 		row = e.rows[e.cursor.y]
-		rowLen := row.Size()
+		rowLen := row.size()
 
 		// Snap to the end of a shorter line from a longer one
 		if e.cursor.x > rowLen {
@@ -147,7 +157,8 @@ func (e *editor) moveCursor (key string) {
 }
 
 func (e *editor) appendRow(s string) {
-	newRow := NewRow(s)
+	newRow := newRow(s)
+	newRow.update()
 	e.rows = append(e.rows, newRow)
 }
 
diff --git a/editor/row.go b/editor/row.go
index fb51558..fc3da1e 100644
--- a/editor/row.go
+++ b/editor/row.go
@@ -1,21 +1,39 @@
 package editor
 
+import "strings"
+
 type row struct {
 	chars []rune
+	render []rune
 }
 
-func NewRow(s string) *row {
+func newRow(s string) *row {
 	var chars []rune
+	var render []rune
 
 	for _, ch := range s {
 		chars = append(chars, ch)
+		render = append(render, ch)
 	}
 
-	return &row {chars}
+	return &row {chars, render}
 }
 
-func (r *row) Size() int {
+func (r *row) size() int {
 	return len(r.chars)
 }
 
+func (r *row) rSize() int {
+	return len(r.render)
+}
+
+func (r *row) update() {
+	r.render = r.render[:0]
+	replacement := strings.Repeat(" ", KiloTabStop)
+
+	str := strings.ReplaceAll(string(r.chars), "\t", replacement)
+	for _, ch := range str {
+		r.render = append(r.render, ch)
+	}
+}
 
diff --git a/editor/row_test.go b/editor/row_test.go
index 0eb07ec..6a9bf16 100644
--- a/editor/row_test.go
+++ b/editor/row_test.go
@@ -4,7 +4,7 @@ import "testing"
 
 func TestNewRow(t *testing.T) {
 	str := "abcdefg"
-	row := NewRow(str)
+	row := newRow(str)
 
 	got := string(row.chars)
 	want := str
@@ -16,9 +16,9 @@ func TestNewRow(t *testing.T) {
 
 func TestRowSize(t *testing.T) {
 	str := "abcdefg"
-	row := NewRow(str)
+	row := newRow(str)
 
-	got := row.Size()
+	got := row.size()
 	want := 7
 
 	if got != want {