Zeitumrechnung möglich?

[DeddyH]

Ich habe es nicht getestet (und evtl. auch wieder zu kompliziert gedacht), aber klappt das hier?

Delphi-Quellcode:

uses DateUtils;

function ArizonaTimeToMEZ(aDateTime: TDateTime): TDateTime;
const
  UTC_DIFF                = 7;
  SUMMERTIME_RELEVANTHOUR = 2;

  function UTCToMEZ(aDateTime: TDateTime): TDateTime;
  var
    SummerTimeStart, SummerTimeEnd: TDateTime;
    Year: word;

    function LastDayOfWeekOfMonth(Year, month: Integer; DayOfWeek: word): TDate;
    var
      temp: TDate;
    begin
      temp := IncMonth(EncodeDate(Year, month, 1));
      Result := IncDay(temp, (DayOfWeek - DayOfTheWeek(temp) + DaysPerWeek)
        mod DaysPerWeek - DaysPerWeek);
    end;

  begin
    Year := YearOf(aDateTime);
    SummerTimeStart := LastDayOfWeekOfMonth(Year, MonthMarch, DaySunday);
    SummerTimeStart := IncHour(DateOf(SummerTimeStart), SUMMERTIME_RELEVANTHOUR);
    SummerTimeEnd := LastDayOfWeekOfMonth(Year, MonthOctober, DaySunday);
    SummerTimeEnd := IncHour(DateOf(SummerTimeEnd), SUMMERTIME_RELEVANTHOUR);
    Result := aDateTime;
    if DateTimeInRange(aDateTime, SummerTimeStart, SummerTimeEnd) then
      Result := IncHour(Result);
  end;

begin
  Result := UTCToMEZ(IncHour(aDateTime, UTC_DIFF));
end;