Small fix for recurring time window testcase

[zhiyuanliang-ms]

Why this PR?

The validation of recurrence configuration has been decoupled from recurrence evaluation. I forgot to update the related testcase. Also, update the implementation to make it more readable, not a bug fix.

related PR: #266

Visible Changes

-changes that are visible to developers using this library-

[rossgrambo]

I don't like this Skip syntax- it seems less readable, could you add a comment why we skip the first?

I'd prefer we don't do a skip and explicitly check if prev == firstDay or if prev != null instead.

[zhiyuanliang-ms]

How about this? Using index to skip the first day, instead of .Skip(1)

  List<DayOfWeek> sortedDaysOfWeek = SortDaysOfWeek(daysOfWeek, firstDayOfWeek);

  DayOfWeek firstDay = sortedDaysOfWeek.First(); // the closest occurrence day to the first day of week

  DayOfWeek prev = firstDay;

  TimeSpan minGap = TimeSpan.FromDays(DaysPerWeek);

  for (int i = 1; i < sortedDaysOfWeek.Count(); i++)
  {
      DayOfWeek dayOfWeek = sortedDaysOfWeek[i];

      TimeSpan gap = TimeSpan.FromDays(CalculateWeeklyDayOffset(dayOfWeek, prev));

      if (gap < minGap)
      {
          minGap = gap;
      }

      prev = dayOfWeek;
  }

[rossgrambo]

Could we take a Set instead so we don't need to Distinct it?

[zhiyuanliang-ms]

I personally like the Distinct one, it is more readable. If we use a set here, we will either need to write two lines of code (1 line for new set and 1 line for ToList) or we will write List<DayOfWeek> result = new HashSet<DayOfWeek>(daysOfWeek).ToList(); I feel this single line ugly. I believe the background implementation of Distinct is based on hash set. Do you have any other concern about using Distinct

[zhiyuanliang-ms]

@rossgrambo I am going to merge this pr. If you have any further concern about what we've discussed in the comments, please let me know.