offer alternative date if there's no slots

src/ui/date-input.imba

@@ -44,7 +44,19 @@ tag date-input
 		<plus-minus value=R.param('date').getFullYear! decr=h.decr_year incr=h.incr_year>
 		<plus-minus value=R.param('date').getMonth!+1 decorate=h.format decr=h.decr_month incr=h.incr_month>
 		<plus-minus value=R.param('date').getDate! decorate=h.format decr=h.decr_day incr=h.incr_day>
-		
+
+let h2 =
+	incr_altday: do R.write 'alt-date', h.modify("Date", 1, R.param('alt-date'))
+	decr_altday: do R.write 'alt-date', h.modify("Date", -1, R.param('alt-date'))
+
+R.setters['alt-date'] = do |v|
+	let d = R.setters.date(v);
+	if d
+		d if d != R.params.date
+	else R.setters.date(h.today!)
+
+R.getters['alt-date'] = do |v| if v then R.getters.date(v) else R.param('date')
+
 tag simple-date-input
 	<self>
-		<plus-minus-v decorate=R.setters.date decr=h.decr_day incr=h.incr_day value=R.param('date')>
+		<plus-minus-v decorate=R.setters.date decr=h2.decr_altday incr=h2.incr_altday value=R.param('alt-date')>