implement alternative window switching

editor/key.go

@@ -88,6 +88,7 @@ func defaultKeyManagers() map[mode.Mode]*key.Manager {
 
 	km.Register(event.New, "c-w", "n")
 	km.Register(event.New, "c-w", "c-n")
+	km.Register(event.Alternative, "\x1e")
 	km.Register(event.FocusWindowDown, "c-w", "down")
 	km.Register(event.FocusWindowDown, "c-w", "c-j")
 	km.Register(event.FocusWindowDown, "c-w", "j")

event/event.go

@@ -108,6 +108,7 @@ const (
 	Enew
 	New
 	Vnew
+	Alternative
 	Wincmd
 	FocusWindowUp
 	FocusWindowDown

window/manager.go

@@ -168,6 +168,9 @@ func (m *Manager) Emit(e event.Event) {
 		} else {
 			m.eventCh <- event.Event{Type: event.Redraw}
 		}
+	case event.Alternative:
+		m.alternative(e)
+		m.eventCh <- event.Event{Type: event.Redraw}
 	case event.Wincmd:
 		if len(e.Arg) == 0 {
 			m.eventCh <- event.Event{Type: event.Error, Error: fmt.Errorf("an argument is required for %s", e.CmdName)}
@@ -311,6 +314,17 @@ func (m *Manager) newWindow(e event.Event, vertical bool) error {
 	return nil
 }
 
+func (m *Manager) alternative(e event.Event) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if e.Count == 0 {
+		m.windowIndex, m.prevWindowIndex = m.prevWindowIndex, m.windowIndex
+	} else if 0 < e.Count && e.Count <= int64(len(m.windows)) {
+		m.windowIndex, m.prevWindowIndex = int(e.Count)-1, m.windowIndex
+	}
+	m.layout = m.layout.Replace(m.windowIndex)
+}
+
 func (m *Manager) wincmd(arg string) error {
 	switch arg {
 	case "n":