public static TimeSpan Span(this TargetTimeline type)
        {
            switch (type)
            {
            case TargetTimeline.Cumulative: return(TimeSpan.MaxValue);

            case TargetTimeline.Daily: return(TimeSpan.FromDays(1));

            case TargetTimeline.Monthly: return(TimeSpan.FromDays(30));

            case TargetTimeline.SingleActivity: return(TimeSpan.FromDays(600));

            case TargetTimeline.Weekly: return(TimeSpan.FromDays(7));
            }
            throw new NotImplementedException();
        }
        public static string AsPostfix(this TargetTimeline type)
        {
            switch (type)
            {
            case TargetTimeline.Cumulative: return("ever");

            case TargetTimeline.Daily: return("in a day");

            case TargetTimeline.Monthly: return("in a month");

            case TargetTimeline.SingleActivity: return("at once");

            case TargetTimeline.Weekly: return("in a week");
            }
            throw new NotImplementedException();
        }