feat: implemented horizontal scroll, tested

Updated lots of pieces with this, but it looks good.

FEATURES.md

@@ -164,8 +164,8 @@
 - [ ] `~` - Swap case of selection
 - [ ] `u` - Lowercase selection
 - [ ] `U` - Uppercase selection
-- [ ] `J` - Join selected lines
 - [ ] `o` - Go to other end of selection
+- [ ] `J` - Join selected lines
 - [ ] `O` - Go to other corner (block mode)
 
 ---

internal/core/window.go

@@ -1,5 +1,7 @@
 package core
 
+import "strconv"
+
 type WinOptions struct {
 	Number         bool
 	RelativeNumber bool
@@ -26,6 +28,7 @@ type Window struct {
 	Anchor Position
 
 	ScrollY int
+	ScrollX int
 	Height  int
 	Width   int
 
@@ -70,17 +73,17 @@ func (w *Window) ClampCursor() {
 	}
 }
 
-// Window.AdjustScroll ensures the cursor stays within the height with scrollOff margins.
+// Window.AdjustScroll ensures the cursor stays within the visible viewport on both axes.
 // Call this after any cursor movement.
 func (w *Window) AdjustScroll() {
-	if w.Height <= 0 {
+	if w.Buffer == nil || w.Height <= 0 {
 		return
 	}
 
-	viewPort := w.ViewportHeight()
+	viewPortHeight := w.ViewportHeight()
 
 	// Effective scrollOff (can't be more than half the viewport)
-	off := min(w.Options.ScrollOff, viewPort/2)
+	off := min(w.Options.ScrollOff, viewPortHeight/2)
 
 	// Cursor too close to top — scroll up
 	if w.Cursor.Line < w.ScrollY+off {
@@ -88,13 +91,29 @@ func (w *Window) AdjustScroll() {
 	}
 
 	// Cursor too close to bottom — scroll down
-	if w.Cursor.Line > w.ScrollY+viewPort-1-off {
-		w.ScrollY = w.Cursor.Line - viewPort + 1 + off
+	if w.Cursor.Line > w.ScrollY+viewPortHeight-1-off {
+		w.ScrollY = w.Cursor.Line - viewPortHeight + 1 + off
 	}
 
 	// Clamp scrollY to valid range
-	maxScroll := max(0, w.Buffer.LineCount()-viewPort)
+	maxScroll := max(0, w.Buffer.LineCount()-viewPortHeight)
 	w.ScrollY = max(0, min(w.ScrollY, maxScroll))
+
+	viewPortWidth := w.ViewportWidth()
+	if viewPortWidth <= 0 {
+		w.ScrollX = 0
+		return
+	}
+
+	if w.Cursor.Col < w.ScrollX {
+		w.ScrollX = w.Cursor.Col
+	} else if w.Cursor.Col >= w.ScrollX+viewPortWidth {
+		w.ScrollX = w.Cursor.Col - viewPortWidth + 1
+	}
+
+	lineLen := w.Buffer.Lines[w.Cursor.Line].Len()
+	maxScrollX := max(0, lineLen-viewPortWidth+1)
+	w.ScrollX = max(0, min(w.ScrollX, maxScrollX))
 }
 
 // ==================================================
@@ -109,6 +128,24 @@ func (w *Window) ViewportHeight() int {
 	return w.Height - 2
 }
 
+func (w *Window) GutterWidth() int {
+	if !(w.Options.Number || w.Options.RelativeNumber) {
+		return 0
+	}
+
+	lineCount := 1
+	if w.Buffer != nil {
+		lineCount = max(1, w.Buffer.LineCount())
+	}
+
+	maxLineLen := len(strconv.Itoa(lineCount))
+	return max(w.Options.GutterSize, maxLineLen+2)
+}
+
+func (w *Window) ViewportWidth() int {
+	return max(0, w.Width-w.GutterWidth())
+}
+
 // ==================================================
 // Setters
 // ==================================================

internal/core/window_test.go

@@ -279,6 +279,115 @@ func TestWindow_AdjustScroll(t *testing.T) {
 			t.Error("cursor should be visible in small viewport")
 		}
 	})
+
+	t.Run("scrolls right when cursor moves past visible width", func(t *testing.T) {
+		buf := NewBufferBuilder().
+			WithLines([]string{"0123456789abcdefghij"}).
+			Build()
+
+		win := NewWindowBuilder().
+			WithBuffer(&buf).
+			WithWidth(12).
+			WithHeight(10).
+			Build()
+
+		win.SetCursorCol(10)
+		win.AdjustScroll()
+
+		if win.ScrollX == 0 {
+			t.Fatal("expected horizontal scroll to move right")
+		}
+
+		viewport := win.ViewportWidth()
+		if win.Cursor.Col < win.ScrollX || win.Cursor.Col >= win.ScrollX+viewport {
+			t.Errorf("cursor at %d not visible in scroll range [%d, %d)",
+				win.Cursor.Col, win.ScrollX, win.ScrollX+viewport)
+		}
+	})
+
+	t.Run("scrolls left when cursor moves back into hidden content", func(t *testing.T) {
+		buf := NewBufferBuilder().
+			WithLines([]string{"0123456789abcdefghij"}).
+			Build()
+
+		win := NewWindowBuilder().
+			WithBuffer(&buf).
+			WithWidth(12).
+			WithHeight(10).
+			Build()
+
+		win.SetCursorCol(14)
+		win.AdjustScroll()
+		if win.ScrollX == 0 {
+			t.Fatal("expected initial horizontal scroll to move right")
+		}
+
+		win.SetCursorCol(2)
+		win.AdjustScroll()
+
+		if win.ScrollX != 2 {
+			t.Errorf("expected horizontal scroll to follow cursor left, got %d", win.ScrollX)
+		}
+	})
+}
+
+func TestWindow_AdjustScrollHorizontalRuneAware(t *testing.T) {
+	tests := []struct {
+		name          string
+		line          string
+		width         int
+		cursorCol     int
+		initialScroll int
+		expected      int
+	}{
+		{
+			name:      "ascii line scrolls using visible columns",
+			line:      "0123456789abcdef",
+			width:     12,
+			cursorCol: 10,
+			expected:  4,
+		},
+		{
+			name:      "multibyte rune line uses rune length not bytes",
+			line:      "abécdefghij",
+			width:     10,
+			cursorCol: 10,
+			expected:  6,
+		},
+		{
+			name:          "moving left pulls scroll back toward cursor",
+			line:          "abécdefghij",
+			width:         10,
+			cursorCol:     2,
+			initialScroll: 6,
+			expected:      2,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			buf := NewBufferBuilder().WithLines([]string{tt.line}).Build()
+			win := NewWindowBuilder().
+				WithBuffer(&buf).
+				WithWidth(tt.width).
+				WithHeight(10).
+				Build()
+
+			win.ScrollX = tt.initialScroll
+			win.SetCursorCol(tt.cursorCol)
+			win.AdjustScroll()
+
+			if win.ScrollX != tt.expected {
+				t.Errorf("ScrollX() = %d, want %d", win.ScrollX, tt.expected)
+			}
+
+			viewport := win.ViewportWidth()
+			if viewport > 0 && (win.Cursor.Col < win.ScrollX || win.Cursor.Col >= win.ScrollX+viewport) {
+				t.Errorf("cursor at %d not visible in scroll range [%d, %d)",
+					win.Cursor.Col, win.ScrollX, win.ScrollX+viewport)
+			}
+		})
+	}
 }
 
 func TestWindow_ViewportHeight(t *testing.T) {
@@ -327,6 +436,34 @@ func TestWindow_ViewportHeight(t *testing.T) {
 	})
 }
 
+func TestWindow_ViewportWidth(t *testing.T) {
+	t.Run("subtracts gutter width", func(t *testing.T) {
+		buf := NewBufferBuilder().WithLines([]string{"line"}).Build()
+		win := NewWindowBuilder().
+			WithBuffer(&buf).
+			WithWidth(20).
+			Build()
+
+		expected := 15
+		if win.ViewportWidth() != expected {
+			t.Errorf("expected viewport width %d, got %d", expected, win.ViewportWidth())
+		}
+	})
+
+	t.Run("returns full width when gutter disabled", func(t *testing.T) {
+		buf := NewBufferBuilder().WithLines([]string{"line"}).Build()
+		win := NewWindowBuilder().
+			WithBuffer(&buf).
+			WithWidth(20).
+			WithOptions(WinOptions{Number: false, RelativeNumber: false, GutterSize: 5, ScrollOff: 8}).
+			Build()
+
+		if win.ViewportWidth() != 20 {
+			t.Errorf("expected viewport width 20, got %d", win.ViewportWidth())
+		}
+	})
+}
+
 func TestWindow_SetOptions(t *testing.T) {
 	t.Run("updates options", func(t *testing.T) {
 		buf := NewBufferBuilder().Build()

internal/editor/integration_scroll_horizontal_test.go

@@ -0,0 +1,86 @@
+package editor
+
+import (
+	"regexp"
+	"strings"
+	"testing"
+
+	"git.gophernest.net/azpect/TextEditor/internal/core"
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+var ansiPattern = regexp.MustCompile(`\x1b\[[0-9;]*m`)
+
+func stripANSI(s string) string {
+	return ansiPattern.ReplaceAllString(s, "")
+}
+
+func firstViewLine(view string) string {
+	lines := strings.Split(view, "\n")
+	if len(lines) == 0 {
+		return ""
+	}
+	return stripANSI(lines[0])
+}
+
+func TestHorizontalScrollRender(t *testing.T) {
+	line := "0123456789abcdef"
+	tm := newTestModelWithTermSize(t, []string{line}, core.Position{Line: 0, Col: 0}, 12, 10)
+
+	for range 10 {
+		sendKeys(tm, "l")
+	}
+
+	m := getFinalModel(t, tm)
+	if m.ActiveWindow().ScrollX != 4 {
+		t.Fatalf("ScrollX() = %d, want 4", m.ActiveWindow().ScrollX)
+	}
+
+	visible := firstViewLine(m.View())
+	if !strings.Contains(visible, "456789a") {
+		t.Fatalf("first visible line = %q, want it to contain %q", visible, "456789a")
+	}
+}
+
+func TestHorizontalScrollRenderReturnsWhenMovingLeft(t *testing.T) {
+	line := "0123456789abcdef"
+	tm := newTestModelWithTermSize(t, []string{line}, core.Position{Line: 0, Col: 0}, 12, 10)
+
+	for range 10 {
+		sendKeys(tm, "l")
+	}
+	for range 10 {
+		sendKeys(tm, "h")
+	}
+
+	m := getFinalModel(t, tm)
+	if m.ActiveWindow().ScrollX != 0 {
+		t.Fatalf("ScrollX() after moving back left = %d, want 0", m.ActiveWindow().ScrollX)
+	}
+
+	visible := firstViewLine(m.View())
+	if !strings.Contains(visible, "0123456") {
+		t.Fatalf("first visible line after moving back left = %q, want it to contain %q", visible, "0123456")
+	}
+}
+
+func TestHorizontalScrollResizeClampWithRunes(t *testing.T) {
+	line := "abécdefghij"
+	tm := newTestModelWithTermSize(t, []string{line}, core.Position{Line: 0, Col: 0}, 10, 10)
+
+	for range 10 {
+		sendKeys(tm, "l")
+	}
+
+	tm.Send(tea.WindowSizeMsg{Width: 12, Height: 10})
+
+	m := getFinalModel(t, tm)
+	if m.ActiveWindow().ScrollX != 5 {
+		t.Fatalf("ScrollX() after resize = %d, want 5", m.ActiveWindow().ScrollX)
+	}
+
+	visible := firstViewLine(m.View())
+	if !strings.Contains(visible, "efghij") {
+		t.Fatalf("first visible line after resize = %q, want it to contain %q", visible, "efghij")
+	}
+}

internal/editor/model.go

@@ -141,8 +141,13 @@ func (m *Model) ClearLastChangeKeys() {
 	m.lastChangeKeys = []string{}
 }
 
+// Handle key also adjusts the scroll anytime an input is pressed.
 func (m *Model) HandleKey(key string) tea.Cmd {
-	return m.input.Handle(m, key)
+	cmd := m.input.Handle(m, key)
+	if len(m.windows) > 0 {
+		m.ActiveWindow().AdjustScroll()
+	}
+	return cmd
 }
 
 func (m *Model) ExitInsertMode() {
@@ -151,7 +156,7 @@ func (m *Model) ExitInsertMode() {
 		m.replayInsert()
 	}
 	if win.Cursor.Col > 0 {
-		win.Cursor.Col--
+		win.SetCursorCol(win.Cursor.Col - 1)
 	}
 	m.mode = core.NormalMode
 	m.insertCount = 0
@@ -271,6 +276,7 @@ func (m *Model) processInsertKey(key string) {
 		}
 		win.SetCursorCol(col + len(key))
 	}
+
 }
 
 // ==================================================

internal/editor/update.go

@@ -48,6 +48,7 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		for i := range m.windows {
 			m.windows[i].Height = msg.Height
 			m.windows[i].Width = msg.Width
+			m.windows[i].AdjustScroll()
 		}
 
 	// TODO: This is not great, totally temporary. But I don't like vim's handling, so this is up to me
@@ -60,6 +61,9 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			scrollAction := motion.ScrollDownPage{Divisor: 4} // Quarter page
 			cmd = scrollAction.Execute(m)
 		}
+		if len(m.windows) > 0 {
+			m.ActiveWindow().AdjustScroll()
+		}
 
 	case tea.KeyMsg:
 		// TODO: This needs to be removed, but for now its required for the tests.
@@ -83,13 +87,9 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				m.CommandOutput().ScrollUp()
 			}
 		} else {
-			cmd = m.input.Handle(m, msg.String())
+			cmd = m.HandleKey(msg.String())
 		}
 	}
 
-	// Keep cursor in view after any update
-	win := m.ActiveWindow()
-	win.AdjustScroll()
-
 	return m, cmd
 }

internal/editor/view.go

@@ -61,12 +61,12 @@ func viewWindow(w *core.Window, t theme.EditorTheme, options core.WinOptions, mo
 	// Draw buffer lines
 	for lineNum := start; lineNum < end; lineNum++ {
 		if lineNum < buf.LineCount() {
-			styleMap := make([]lipgloss.Style, len([]rune(buf.Line(lineNum))))
+			line := buf.Lines[lineNum]
+			styleMap := make([]lipgloss.Style, line.Len())
 			if sx != nil {
 				styleMap = sx.LineStyleMap(buf, lineNum, t)
 			}
-			line := drawLine(w, t, options, mode, buf.Line(lineNum), lineNum, styleMap)
-			view.WriteString(line)
+			view.WriteString(drawLine(w, t, options, mode, line, lineNum, styleMap))
 		} else {
 			view.WriteString(strings.Repeat(t.Background.Render(" "), w.Width))
 		}
@@ -82,46 +82,49 @@ func viewWindow(w *core.Window, t theme.EditorTheme, options core.WinOptions, mo
 
 // drawLine: Renders a single line with syntax highlighting, cursor, and visual selection.
 // Handles gutter, cursor rendering, and visual mode highlighting.
-func drawLine(w *core.Window, t theme.EditorTheme, options core.WinOptions, mode core.Mode, line string, lineNumber int, styleMap []lipgloss.Style) string {
+func drawLine(w *core.Window, t theme.EditorTheme, options core.WinOptions, mode core.Mode, line *core.GapBuffer, lineNumber int, styleMap []lipgloss.Style) string {
 	var view strings.Builder
-	runes := []rune(line)
+	lineLen := line.Len()
 
 	// Draw gutter first
 	gutter := drawGutter(w, t, options, lineNumber)
 	view.WriteString(gutter)
+	contentWidth := w.ViewportWidth()
+	if contentWidth <= 0 {
+		return view.String()
+	}
+
+	// Draw visible content slice only
+	startCol := max(0, w.ScrollX)
+	for screenCol := range contentWidth {
+		col := startCol + screenCol
 
-	// Now draw the line content
-	for col := 0; col <= len(runes); col++ {
 		// Current char is cursor
 		if col == w.Cursor.Col && lineNumber == w.Cursor.Line {
-			if col < len(runes) {
+			if col < lineLen {
 				cur := t.Cursor(mode, styleMap[col])
-				view.WriteString(cur.Render(string(runes[col])))
+				view.WriteString(cur.Render(string(line.RuneAt(col))))
 			} else {
 				view.WriteString(t.DefaultCursor(mode).Render(" "))
 			}
+			continue
+		}
 
-			// Not cursor, but not end
-		} else if col < len(runes) {
+		if col < lineLen {
 			s := styleMap[col]
 			if mode.IsVisualMode() && posInsideSelection(w, mode, col, lineNumber) {
 				vis := t.VisualHighlightWithTextColor(s)
-				view.WriteString(vis.Render(string(runes[col])))
+				view.WriteString(vis.Render(string(line.RuneAt(col))))
 			} else {
-				view.WriteString(s.Render(string(runes[col])))
+				view.WriteString(s.Render(string(line.RuneAt(col))))
 			}
-			// Allow highlight on blank lines or chars
 		} else if mode.IsVisualMode() && posInsideSelection(w, mode, col, lineNumber) {
 			view.WriteString(t.VisualHightlight.Render(" "))
+		} else {
+			view.WriteString(t.Background.Render(" "))
 		}
 	}
 
-	// Pad remainder of line to window width with background color
-	dif := w.Width - lipgloss.Width(view.String())
-	if dif > 0 {
-		view.WriteString(strings.Repeat(t.Background.Render(" "), dif))
-	}
-
 	return view.String()
 }
 

v0.1.md

@@ -20,8 +20,8 @@
 - [ ] Better command-mode autocomplete/hints
 - [ ] Configuration file support (~/.gimrc or similar)
 - [ ] ~Persistent undo history~
-- [ ] Line wrapping display option
-- [ ] Horozontal scroll
+- [ ] ~Line wrapping display option~
+- [ ] Horizontal scroll
 - [ ] Handle large files gracefully (>10k lines) [Pretty sure this is fine]
 - [ ] Alternate buffer implementation