A way to generate the dates that need to appear on a calendar page

CalendarDates.cs

void Main()
{
  var refDate = DateTime.Today.AddMonths(-1);
	
	var start = refDate.StartOfMonth().Backwards().FirstOrDefault (d => d.DayOfWeek == DayOfWeek.Monday);
	var end = refDate.EndOfMonth().Forwards().FirstOrDefault (d => d.DayOfWeek == DayOfWeek.Sunday);
	
	start.UpTo(end).ToArray().Dump();
}


public static class Ext
{
	public static DateTime StartOfMonth(this DateTime refDate)
	{
		return new DateTime(refDate.Year, refDate.Month, 1);
	}
	
	public static DateTime EndOfMonth(this DateTime refDate)
	{
		return refDate.AddMonths(1).StartOfMonth().AddDays(-1);
	}

	public static IEnumerable<DateTime> UpTo(this DateTime start, DateTime end)
	{
		return start.Forwards().TakeWhile(x => x <= end);
	}
	
	public static IEnumerable<DateTime> Forwards(this DateTime start)
	{
		return start.Generate(x => x.AddDays(1));
	}
	
	public static IEnumerable<DateTime> Backwards(this DateTime start)
	{
		return start.Generate(x => x.AddDays(-1));
	}
 
	public static IEnumerable<T> Generate<T>(this T start, Func<T, T> getNext)
	{
		var current = start;
		while(true)
		{
			yield return current;
			current = getNext(current);
		}
	}
}