add scrollable functionality for fstree

fstree/fstree.go

@@ -52,6 +52,8 @@ type FsTree struct {
 	selectedNode *FsNode
 	hoveredNode  *FsNode
 	errMsg       string
+	height       int
+	width        int
 }
 
 // ==================== Bubble Tea Interface Implementation ====================
@@ -61,6 +63,9 @@ func (t *FsTree) Init() tea.Cmd {
 
 func (t *FsTree) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	switch m := msg.(type) {
+	case tea.WindowSizeMsg:
+		t.width = m.Width
+		t.height = m.Height
 	case tea.KeyMsg:
 		t.errMsg = ""
 		switch m.String() {
@@ -117,7 +122,33 @@ func (t *FsTree) View() string {
 
 	builder := &strings.Builder{}
 	t.renderNode(t.root, 0, builder)
-	return builder.String()
+	rendered := builder.String()
+
+	// clamp to height around selected node
+	if t.selectedNode != nil {
+		lines := strings.Split(rendered, "\n")
+		totalLines := len(lines)
+		selectedLine := t.selectedNode.line
+
+		halfHeight := t.height / 2
+		startLine := selectedLine - halfHeight
+		if startLine < 0 {
+			startLine = 0
+		}
+		endLine := startLine + t.height
+		if endLine > totalLines {
+			endLine = totalLines
+			startLine = endLine - t.height
+			if startLine < 0 {
+				startLine = 0
+			}
+		}
+
+		clampedLines := lines[startLine:endLine]
+		rendered = strings.Join(clampedLines, "\n")
+	}
+
+	return rendered
 }
 
 // ==================== FsTree helper methods ====================

main.go

@@ -98,12 +98,20 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	case tea.WindowSizeMsg:
 		m.terminalWidth = msg.Width
 		m.terminalHeight = msg.Height
-		m.viewport.Width = msg.Width - m.width - 1
-		m.viewport.Height = msg.Height
+		if m.tree != nil {
+			m.tree.Update(tea.WindowSizeMsg{
+				Height: m.terminalHeight,
+				Width:  m.terminalWidth,
+			})
+		}
 		return m, nil
 	case treeLoadedMsg:
 		m.tree = msg.tree
 		m.loading = false
+		m.tree.Update(tea.WindowSizeMsg{
+			Height: m.terminalHeight,
+			Width:  m.terminalWidth,
+		})
 		return m, nil
 	case spinner.TickMsg:
 		var cmd tea.Cmd