Add stack UI container

lib/ui/stack.go

@@ -0,0 +1,73 @@
+package ui
+
+import (
+	"fmt"
+
+	tb "github.com/nsf/termbox-go"
+)
+
+type Stack struct {
+	children []Drawable
+	onInvalidate func(d Drawable)
+}
+
+func NewStack() *Stack {
+	return &Stack{}
+}
+
+func (stack *Stack) OnInvalidate(onInvalidate func (d Drawable)) {
+	stack.onInvalidate = onInvalidate
+}
+
+func (stack *Stack) Invalidate() {
+	if stack.onInvalidate != nil {
+		stack.onInvalidate(stack)
+	}
+}
+
+func (stack *Stack) Draw(ctx *Context) {
+	if len(stack.children) > 0 {
+		stack.Peek().Draw(ctx)
+	} else {
+		cell := tb.Cell{
+			Fg: tb.ColorDefault,
+			Bg: tb.ColorDefault,
+			Ch: ' ',
+		}
+		ctx.Fill(0, 0, ctx.Width(), ctx.Height(), cell)
+	}
+}
+
+func (stack *Stack) Push(d Drawable) {
+	if len(stack.children) != 0 {
+		stack.Peek().OnInvalidate(nil)
+	}
+	stack.children = append(stack.children, d)
+	d.OnInvalidate(stack.invalidateFromChild)
+	stack.Invalidate()
+}
+
+func (stack *Stack) Pop() Drawable {
+	if len(stack.children) == 0 {
+		panic(fmt.Errorf("Tried to pop from an empty UI stack"))
+	}
+	d := stack.children[len(stack.children)-1]
+	stack.children = stack.children[:len(stack.children)-1]
+	stack.Invalidate()
+	d.OnInvalidate(nil)
+	if len(stack.children) != 0 {
+		stack.Peek().OnInvalidate(stack.invalidateFromChild)
+	}
+	return d
+}
+
+func (stack *Stack) Peek() Drawable {
+	if len(stack.children) == 0 {
+		panic(fmt.Errorf("Tried to peek from an empty stack"))
+	}
+	return stack.children[len(stack.children)-1]
+}
+
+func (stack *Stack) invalidateFromChild(d Drawable) {
+	stack.Invalidate()
+}