widgets: add dialog interface

Implement an interface for aerc's dialog implementation. Provide dialogs
the ability to set their own height and width of their drawing context.

Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>

widgets/aerc.go

@@ -187,7 +187,14 @@ func (aerc *Aerc) Draw(ctx *ui.Context) {
 	aerc.grid.Draw(ctx)
 	if aerc.dialog != nil {
 		if w, h := ctx.Width(), ctx.Height(); w > 8 && h > 4 {
-			aerc.dialog.Draw(ctx.Subcontext(4, h/2-2, w-8, 4))
+			if d, ok := aerc.dialog.(Dialog); ok {
+				start, height := d.ContextHeight()
+				aerc.dialog.Draw(
+					ctx.Subcontext(4, start(h),
+						w-8, height(h)))
+			} else {
+				aerc.dialog.Draw(ctx.Subcontext(4, h/2-2, w-8, 4))
+			}
 		}
 	}
 }

widgets/dialog.go

@@ -0,0 +1,24 @@
+package widgets
+
+import (
+	"git.sr.ht/~rjarry/aerc/lib/ui"
+)
+
+type Dialog interface {
+	ui.DrawableInteractive
+	ContextHeight() (func(int) int, func(int) int)
+}
+
+type dialog struct {
+	ui.DrawableInteractive
+	y func(int) int
+	h func(int) int
+}
+
+func (d *dialog) ContextHeight() (func(int) int, func(int) int) {
+	return d.y, d.h
+}
+
+func NewDialog(d ui.DrawableInteractive, y func(int) int, h func(int) int) Dialog {
+	return &dialog{DrawableInteractive: d, y: y, h: h}
+}