1 files changed, 70 insertions, 0 deletions
diff --git a/gui/widget/focus.go b/gui/widget/focus.go
new file mode 100644
index 0000000..e2d1074
--- /dev/null
+++ b/gui/widget/focus.go
@@ -0,0 +1,70 @@
+package widget
+
+import "image"
+
+// Focus keeps track of the currently selected widget.
+// A widget receives true when it gains focus and false when it loses focus.
+type Focus struct {
+	Widgets [][]chan bool
+	p       image.Point // coordinates of currently focused widget
+}
+
+func NewFocus(rows []int) Focus {
+	f := Focus{
+		make([][]chan bool, len(rows)),
+		image.Point{},
+	}
+	for i := range f.Widgets {
+		f.Widgets[i] = make([]chan bool, rows[i])
+		for j := range f.Widgets[i] {
+			f.Widgets[i][j] = make(chan bool)
+		}
+	}
+	return f
+}
+
+func (f *Focus) Close() {
+	for i := range f.Widgets {
+		for j := range f.Widgets[i] {
+			close(f.Widgets[i][j])
+		}
+	}
+}
+
+func (f *Focus) Focus(focus bool) {
+	f.Widgets[f.p.Y][f.p.X] <- focus
+}
+
+func (f *Focus) Left() {
+	f.Focus(false)
+	if f.p.X <= 0 {
+		f.p.X = len(f.Widgets[f.p.Y]) - 1
+	} else {
+		f.p.X--
+	}
+	f.Focus(true)
+}
+
+func (f *Focus) Right() {
+	f.Focus(false)
+	f.p.X = (f.p.X + 1) % len(f.Widgets[f.p.Y])
+	f.Focus(true)
+}
+
+func (f *Focus) Up() {
+	f.Focus(false)
+	if f.p.Y <= 0 {
+		f.p.Y = len(f.Widgets) - 1
+	} else {
+		f.p.Y--
+	}
+	f.p.X = min(f.p.X, len(f.Widgets[f.p.Y])-1)
+	f.Focus(true)
+}
+
+func (f *Focus) Down() {
+	f.Focus(false)
+	f.p.Y = (f.p.Y + 1) % len(f.Widgets)
+	f.p.X = min(f.p.X, len(f.Widgets[f.p.Y])-1)
+	f.Focus(true)
+}