linqpad/FiscalMonthResolver/Test FiscalMonthResolver.linq

<Query Kind="Program">
  <Connection>
    <ID>eae63890-d1e5-4142-8086-9d954a38c63c</ID>
    <Persist>true</Persist>
    <Server>D0011-SQL-01.sdt.local</Server>
    <Database>jazz tst Edward Elmhurst 20210127.1</Database>
    <ShowServer>true</ShowServer>
  </Connection>
  <Namespace>System.Collections.ObjectModel</Namespace>
</Query>

void Main()
{
	var fmr = new FiscalMonthResolver(from fm in DimFiscalMonths
									  select new FiscalMonth
									  {
										  MemberGUID = fm.MemberGUID,
										  FiscalMonthID = fm.FiscalMonthID,
										  SortOrder = fm.SortOrder,
										  FiscalMonthCode = int.Parse(fm.FiscalMonthCode),
										  Name = fm.Name,
										  Abbreviation = fm.Abbreviation,
										  DaysInMonth = fm.DaysInMonth,
										  YTDDaysInMonth = fm.YTDDaysInMonth,
										  QuarterID = fm.QuarterID,
										  MonthColumnName = fm.MonthColumnName,
										  TransactionID = fm.TransactionID,
										  DaysInLeapYearMonth = fm.DaysInLeapYearMonth,
										  YTDDaysInLeapYearMonth = fm.YTDDaysInLeapYearMonth,
										  IsReal = fm.IsReal
									  });

	var config = new Configuration(fmr);
	var fiscalMonths = fmr.AllFiscalMonths;
	var startDate = new DateTime(2020, 1, 1);
	var endDate = startDate.AddYears(1).AddDays(-1);
	config.GetYearMonths(startDate, endDate).Dump();

	startDate = config.GetFiscalYearStartDate();
	endDate = config.GetFiscalYearEndDate();
	config.GetYearMonths(startDate, endDate).Dump();
	fiscalMonths.Where(fm => fm.IsReal).Dump();
}

// Define other methods and classes here

public class Configuration
{
	public int FiscalYearID = 2020;
	public FiscalMonthResolver FiscalMonthResolver;

	public Configuration(FiscalMonthResolver fmr)
	{
		FiscalMonthResolver = fmr;
	}

	public DateTime GetFiscalYearStartDate()
	{
		return GetFiscalYearEndDate().AddYears(-1).AddDays(1);
	}

	public DateTime GetFiscalYearEndDate()
	{
		var lastFiscalMonth = FiscalMonthResolver.LastFiscalMonth.FiscalMonthID;
		return new DateTime(FiscalYearID, lastFiscalMonth, DateTime.DaysInMonth(FiscalYearID, lastFiscalMonth));
	}

	public IList<YearMonth> GetYearMonths(DateTime startDate, DateTime endDate)
	{
		var ym = new List<YearMonth>();
		var currentMonth = startDate;
		$"\r\nCurrent: {currentMonth:d} - End: {endDate:d}".Dump();
		while (currentMonth <= endDate)
		{
			var fiscalMonth = FiscalMonthResolver.ConvertToFiscalYearMonth(currentMonth);
			fiscalMonth.Dump();
			ym.Add(new YearMonth(fiscalMonth.Year, currentMonth.Year,
			FiscalMonthResolver.GetByFiscalMonthId(currentMonth.Month)));
			currentMonth = currentMonth.AddMonths(1);
		}
		return ym;
	}
}

public interface IFiscalMonthResolver

{
	FiscalMonth FirstFiscalMonth { get; }

	FiscalMonth LastFiscalMonth { get; }

	FiscalMonth GetByFiscalMonthId(int fiscalMonthId);

	FiscalMonth GetByFiscalMonthSortOrder(int sortOrder);

	List<FiscalMonth> AllFiscalMonths { get; }
}

public class FiscalMonthResolver : IFiscalMonthResolver
{
	public FiscalMonthResolver(IEnumerable<FiscalMonth> fiscalMonths)
	{
		AllFiscalMonths = fiscalMonths.ToList();
	}

	public FiscalMonth FirstFiscalMonth => GetByFiscalMonthSortOrder(1);

	public FiscalMonth LastFiscalMonth => GetByFiscalMonthSortOrder(12);

	public List<FiscalMonth> AllFiscalMonths { get; set; }

	public FiscalMonth GetByFiscalMonthId(int fiscalMonthId)
	{
		return AllFiscalMonths.FirstOrDefault(afm => afm.FiscalMonthID == fiscalMonthId);
	}

	public FiscalMonth GetByFiscalMonthSortOrder(int sortOrder)
	{
		return AllFiscalMonths.FirstOrDefault(afm => afm.SortOrder == sortOrder);
	}

	public DateTime ConvertToFiscalYearMonth(DateTime calendarYearMonth)
	{
		var fiscalYearID = calendarYearMonth.Month <= LastFiscalMonth.FiscalMonthID
		? calendarYearMonth.Year
		: calendarYearMonth.Year + 1;
		return new DateTime(fiscalYearID, calendarYearMonth.Month, 1);
	}
}

public class FiscalMonth
{
	internal Guid MemberGUID { get; set; }
	public byte FiscalMonthID { get; set; }
	public byte SortOrder { get; set; }
	public int FiscalMonthCode { get; set; }
	public String Name { get; set; }
	public String Abbreviation { get; set; }
	public Int32 DaysInMonth { get; set; }
	public Int32 YTDDaysInMonth { get; set; }
	public byte QuarterID { get; set; }
	public String MonthColumnName { get; set; }
	internal String Version { get; set; }
	internal Guid HistoryItemGUID { get; set; }
	internal Int32 TransactionID { get; set; }
	public Int32 DaysInLeapYearMonth { get; set; }
	public Int32 YTDDaysInLeapYearMonth { get; set; }
	public Boolean IsReal { get; set; }

}

public class YearMonth
{
	public readonly int FiscalYear;
	public readonly int CalendarYear;

	internal readonly FiscalMonth FiscalMonth;

	public readonly DateTime FiscalYearMonth;

	public readonly DateTime CalendarYearMonth;

	#region Helper Properties  to corelate to database column names

	public int FiscalYearID => FiscalYear;

	/// <summary>
	/// This is calendar month and FiscalMonth.SortOrder is the real FiscalMonth
	/// we put it here so that we don't frikin confuse ourself between fiscalmonth and calendarmonth :x
	/// </summary>
	public int FiscalMonthID => FiscalMonth.FiscalMonthID;

	#endregion

	internal YearMonth(int fiscalYear, int calendarYear, FiscalMonth fiscalMonth)
	{
		FiscalYear = fiscalYear;
		CalendarYear = calendarYear;
		FiscalMonth = fiscalMonth;

		FiscalYearMonth = new DateTime(fiscalYear, fiscalMonth.SortOrder, 1);
		CalendarYearMonth = new DateTime(calendarYear, fiscalMonth.FiscalMonthID, 1);
	}
}