PanelContainer: Implement cycling selection

main.go

@@ -295,7 +295,11 @@ func main() {
 
 	panelMenu := ui.NewMenu("Panel", 0, &theme)
 
-	panelMenu.AddItems([]ui.Item{&ui.ItemEntry{Name: "Focus Up", QuickChar: -1, Shortcut: "Alt+Up", Callback: func() {
+	panelMenu.AddItems([]ui.Item{&ui.ItemEntry{Name: "Focus Next", Shortcut: "Alt+.", Callback: func() {
+		panelContainer.SelectNext()
+	}}, &ui.ItemEntry{Name: "Focus Prev", Shortcut: "Alt+,", Callback: func() {
+		panelContainer.SelectPrev()
+	}}, &ui.ItemEntry{Name: "Focus Up", QuickChar: -1, Shortcut: "Alt+Up", Callback: func() {
 		
 	}}, &ui.ItemEntry{Name: "Focus Down", QuickChar: -1, Shortcut: "Alt+Down", Callback: func() {
 

ui/panel.go

@@ -69,27 +69,42 @@ func (p *Panel) UpdateSplits() {
 }
 
 // Same as EachLeaf, but returns true if any call to `f` returned true.
-func (p *Panel) eachLeaf(f func(*Component) bool) bool {
+func (p *Panel) eachLeaf(rightMost bool, f func(*Panel) bool) bool {
 	switch p.Kind {
+	case PanelKindEmpty:
+		fallthrough
 	case PanelKindSingle:
-		return f(&p.Left)
+		return f(p)
+
 	case PanelKindSplitVert:
 		fallthrough
 	case PanelKindSplitHor:
-		if p.Left.(*Panel).eachLeaf(f) {
+		if rightMost {
+			if p.Right.(*Panel).eachLeaf(rightMost, f) {
 				return true
 			}
-		return p.Right.(*Panel).eachLeaf(f)
+			return p.Left.(*Panel).eachLeaf(rightMost, f)
+		} else {
+			if p.Left.(*Panel).eachLeaf(rightMost, f) {
+				return true
+			}
+			return p.Right.(*Panel).eachLeaf(rightMost, f)
+		}
+
 	default:
 		return false
 	}
 }
 
-// EachLeaf visits the entire tree in left-most order, and calls function `f`
-// at each individual Component (never for Panels). If the function `f` returns
-// true, then visiting stops.
-func (p *Panel) EachLeaf(f func(*Component) bool) {
-	p.eachLeaf(f)
+// EachLeaf visits the entire tree, and calls function `f` at each leaf Panel.
+// If the function `f` returns true, then visiting stops. if `rtl` is true,
+// the tree is traversed in right-most order. The default is to traverse
+// in left-most order.
+//
+// The caller of this function can safely assert that Panel's Kind is always
+// either `PanelKindSingle` or `PanelKindEmpty`.
+func (p *Panel) EachLeaf(rightMost bool, f func(*Panel) bool) {
+	p.eachLeaf(rightMost, f)
 }
 
 // IsLeaf returns whether the Panel is a leaf or not. A leaf is a panel with

ui/panelcontainer.go

@@ -266,6 +266,36 @@ func (c *PanelContainer) UnfloatSelected(kind SplitKind) bool {
 	return c.SetFloatingFocused(true)
 }
 
+func (c *PanelContainer) selectNext(rightMost bool) {
+	var nextIsIt bool
+	c.root.EachLeaf(rightMost, func(p *Panel) bool {
+		if nextIsIt {
+			c.selected = &p
+			nextIsIt = false
+			return true
+		} else if p == *c.selected {
+			nextIsIt = true
+		}
+		return false
+	})
+
+	// This boolean must be false if we found the next leaf.
+	// Therefore, if it is true, c.selected was the last leaf
+	// of the tree. We need to wrap around to the first leaf.
+	if nextIsIt {
+		// This gets the first leaf in left-most or right-most order
+		c.root.EachLeaf(rightMost, func(p *Panel) bool { c.selected = &p; return true })
+	}
+}
+
+func (c *PanelContainer) SelectNext() {
+	c.selectNext(false)
+}
+
+func (c *PanelContainer) SelectPrev() {
+	c.selectNext(true)
+}
+
 func (c *PanelContainer) Draw(s tcell.Screen) {
 	c.root.Draw(s)
 	for i := len(c.floating)-1; i >= 0; i-- {