add support to dynamically adjust file tree width

pkg/ui/keys.go

@@ -33,6 +33,8 @@ type KeyMap struct {
 	ToggleHelp            key.Binding
 	ToggleMessage         key.Binding
 	ToggleSelection       key.Binding
+	IncreaseFileTreeWidth key.Binding
+	DecreaseFileTreeWidth key.Binding
 }
 
 var keys = &KeyMap{
@@ -156,6 +158,14 @@ var keys = &KeyMap{
 		key.WithKeys("v"),
 		key.WithHelp("v", "toggle selection"),
 	),
+	IncreaseFileTreeWidth: key.NewBinding(
+		key.WithKeys(">"),
+		key.WithHelp(">", "increase file tree width"),
+	),
+	DecreaseFileTreeWidth: key.NewBinding(
+		key.WithKeys("<"),
+		key.WithHelp("<", "decrease file tree width"),
+	),
 }
 
 func KeyGroups() [][]key.Binding {
@@ -171,6 +181,7 @@ func KeyGroups() [][]key.Binding {
 		keys.CtrlU,
 		keys.ScrollLeft,
 		keys.ScrollRight,
+		keys.IncreaseFileTreeWidth,
 	}, {
 		keys.ToggleFileTree,
 		keys.SearchFiles,
@@ -183,6 +194,7 @@ func KeyGroups() [][]key.Binding {
 		keys.ToggleDiffView,
 		keys.ToggleIconStyle,
 		keys.ToggleSelection,
+		keys.DecreaseFileTreeWidth,
 	}, {
 		keys.ToggleMessage,
 		keys.ToggleHelp,

pkg/ui/tui.go

@@ -361,6 +361,15 @@ func (m mainModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		case key.Matches(msg, keys.CtrlD, keys.CtrlU, keys.CtrlE, keys.CtrlY):
 			m.diffViewer, cmd = m.diffViewer.Update(msg)
 			cmds = append(cmds, cmd)
+
+		case key.Matches(msg, keys.IncreaseFileTreeWidth):
+			m, cmd = m.handleSidebarResize(minResizeStep)
+			cmds = append(cmds, cmd)
+
+		case key.Matches(msg, keys.DecreaseFileTreeWidth):
+			m, cmd = m.handleSidebarResize(-minResizeStep)
+			cmds = append(cmds, cmd)
+
 		default:
 			if m.activePanel == DiffViewerPanel {
 				m.diffViewer, cmd = m.diffViewer.Update(msg)
@@ -1324,6 +1333,38 @@ func (m mainModel) handleSidebarDrag(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
 	return m, tea.Batch(cmds...)
 }
 
+func (m mainModel) handleSidebarResize(resize int) (mainModel, tea.Cmd) {
+	if m.searchingFiles {
+		return m, nil
+	}
+
+	// Clamp to reasonable bounds.
+	minWidth := sidebarMinWidth
+	maxWidth := m.width / 2
+	newWidth := max(minWidth, min(maxWidth, m.sidebarWidth()+resize))
+
+	// Hide sidebar if resized below threshold.
+	if newWidth < sidebarHideWidth {
+		m.isShowingFileTree = false
+		cmd := m.diffViewer.SetSize(m.width, m.mainContentHeight())
+		return m, cmd
+	}
+
+	// TODO: for some reason setting a value smaller than minResizeStep
+	// will garble up the output when resizing. I have no idea why.
+	if abs(newWidth-m.sidebarWidth()) < minResizeStep {
+		return m, nil
+	}
+
+	// Resize components.
+	cmds := []tea.Cmd{}
+
+	cmds = append(cmds, m.diffViewer.SetSize(m.width-newWidth, m.mainContentHeight()))
+	m.fileTree.SetSize(newWidth-1, m.mainContentHeight()-searchHeight-1)
+
+	return m, tea.Batch(cmds...)
+}
+
 func abs(x int) int {
 	if x < 0 {
 		return -x