I realy love the idea of your app. By showing completed task and uncompeletd task seprately. User can swip right to mark a task as done, but what if tehy did it by mistake?. The user may wants to mark the task as uncompleted, but there's no way to do it on history tab. It seems all I can do at hisgtory tab is just deleting task which is marked as done.
I widsh there is a mark as uncompeletd button to show up when user slid task swipe in history tab just like Tasks tab.