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???? public ? static ? class ?DateUtility
????{
???????? /// ? <summary>
???????? /// ?Returns?the?first?day?of?the?year?for?a?given?date
???????? /// ? </summary>
???????? /// ? <param?name="date"></param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?BeginOfYear(DateTime?date)
????????{
???????????? return ? new ?DateTime(date.Year,? 1 ,? 1 );
????????}

???????? /// ? <summary>
???????? /// ?Returns?the?last?day?of?the?year?for?a?given?date
???????? /// ? </summary>
???????? /// ? <param?name="date"></param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?EndOfYear(DateTime?date)
????????{
???????????? return ? new ?DateTime(date.Year,? 12 ,? 31 );
????????}

???????? /// ? <summary>
???????? /// ?Returns?the?first?day?of?a?month?for?a?given?date
???????? /// ? </summary>
???????? /// ? <param?name="date"></param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?BeginOfMonth(DateTime?date)
????????{
???????????? return ? new ?DateTime(date.Year,?date.Month,? 1 );
????????}

???????? /// ? <summary>
???????? /// ?Returns?the?last?day?of?a?month?for?a?given?date
???????? /// ? </summary>
???????? /// ? <param?name="date"> Date </param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?EndOfMonth(DateTime?date)
????????{
???????????? int ?year? = ?date.Year;
???????????? int ?month? = ?date.Month;
???????????? if ?(month? == ? 12 )
????????????{
????????????????year ++ ;
????????????????month = 1 ;
????????????}
???????????? else
????????????????month ++ ;
???????????? return ? new ?DateTime(year,month, 1 ).AddDays( - 1 );
????????}


???????? /// ? <summary>
???????? /// ?Returns?the?first?day?of?a?quarter
???????? /// ? </summary>
???????? /// ? <param?name="date"></param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?BeginOfQuarter(DateTime?date)
????????{
???????????? int ?month? = ?(((date.Month? - 1 )? / ? 3 ) * 3 ) + 1 ;
???????????? return ? new ?DateTime(date.Year,?month,? 1 );
????????}

???????? /// ? <summary>
???????? /// ?Returns?the?last?day?of?a?quarter
???????? /// ? </summary>
???????? /// ? <param?name="date"> Date </param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?EndOfQuarter(DateTime?date)
????????{
???????????? return ?BeginOfQuarter(BeginOfMonth(date).AddMonths( + 3 )).AddDays( - 1 );
????????}

???????? /// ? <summary>
???????? /// ?Check?if?the?date?is?in?a?leapyear
???????? /// ? </summary>
???????? /// ? <param?name="date"> Date </param>
???????? /// ? <returns></returns>
???????? public ? static ? bool ?LeapYear(DateTime?date)
????????{
???????????? int ?year? = ?date.Year;
???????????? return ?(year? % ? 4 ? == ? 0 )? && ?((year? % ? 100 ? != ? 0 )? || ?(year? % ? 400 ? == ? 0 ));
????????}

???????? /// ? <summary>
???????? /// ?Caclulates?the?weeknumber?for?a?given?date
???????? /// ? </summary>
???????? /// ? <param?name="date"> Date </param>
???????? /// ? <returns></returns>
???????? public ? static ? int ?WeekOfYear(DateTime?date)
????????{????????????
???????????? int []?t1? = ? new ? int [ 7 ]?{ - 1 ,?? 0 ,?? 1 ,?? 2 ,?? 3 ,? - 3 ,? - 2 };
???????????? int []?t2? = ? new ? int [ 7 ]?{ - 4 ,?? 2 ,?? 1 ,?? 0 ,? - 1 ,? - 2 ,? - 3 };

????????????DateTime?newYear? = ?BeginOfYear(date);
???????????? int ?doy1? = ?date.DayOfYear? + ?t1[( int )newYear.DayOfWeek];
???????????? int ?doy2? = ?date.DayOfYear? + ?t2[( int )date.DayOfWeek];

???????????? if ?(doy1? <= ? 0 )?
???????????????? return ?WeekOfYear(newYear.AddDays( - 1 ));
???????????? else
???????????????? if ?(doy2? >= ?EndOfYear(newYear).DayOfYear?)
???????????????????? return ? 1 ;
???????????????? else
???????????????????? return ?(doy1 - 1 ) / 7 ? + 1 ;
????????}

???????? /// ? <summary>
???????? /// ?Determines?how?much?days?a?month?has
???????? /// ? </summary>
???????? /// ? <param?name="date"> Date </param>
???????? /// ? <returns> Number?of?days?in?the?month </returns>
???????? public ? static ? int ?DaysInMonth(DateTime?date)
????????{
???????????? short []?daysPerMonth? = ? new ? short [ 12 ]?{? 31 ,? 28 ,? 31 ,? 30 ,? 31 ,? 30 ,? 31 ,? 31 ,? 30 ,? 31 ,? 30 ,? 31 ?};
???????????? int ?month? = ?date.Month;
???????????? if ?(month? == ? 2 ? && ?LeapYear(date))
???????????????? return ?daysPerMonth[month? - ? 1 ]? + ? 1 ;
???????????? else
???????????????? return ?daysPerMonth[month? - ? 1 ];
????????}


???????? /// ? <summary>
???????? /// ?Return?the?duration?between?two?dates?in?months
???????? /// ? </summary>
???????? /// ? <param?name="start"></param>
???????? /// ? <param?name="end"></param>
???????? /// ? <returns></returns>
???????? public ? static ? int ?AgeInMonths(DateTime?start,?DateTime?end)
????????{
???????????? return ?(end.Year - start.Year)? * ? 12 ? + ?(end.Month - start.Month);
????????}

???????? /// ? <summary>
???????? /// ?Return?the?duration?between?two?dates?in?years
???????? /// ? </summary>
???????? /// ? <param?name="start"></param>
???????? /// ? <param?name="end"></param>
???????? /// ? <returns></returns>
???????? public ? static ? int ?AgeInYears(DateTime?start,?DateTime?end)
????????{
???????????? return ?AgeInMonths(start,?end)? / ? 12 ;
????????}

???????? /// ? <summary>
???????? /// ?Return?the?duration?until?today?in?months
???????? /// ? </summary>
???????? /// ? <param?name="start"></param>
???????? /// ? <returns></returns>
???????? public ? static ? int ?AgeInMonths(DateTime?start)
????????{
???????????? return ?AgeInMonths(start,?DateTime.Today);
????????}

???????? /// ? <summary>
???????? /// ?Return?the?duration?until?today?in?years
???????? /// ? </summary>
???????? /// ? <param?name="start"></param>
???????? /// ? <param?name="end"></param>
???????? /// ? <returns></returns>
???????? public ? static ? int ?AgeInYears(DateTime?start)
????????{
???????????? return ?AgeInYears(start,?DateTime.Today);
????????}

???????? /// ? <summary>
???????? /// ?Calculate?the?easter?holiday?for?a?year
???????? /// ? </summary>
???????? /// ? <param?name="year"></param>
???????? /// ? <returns></returns>
???????? public ? static ?DateTime?Easter( int ?year)
????????{
???????????? int ?month;
???????????? int ?day;

???????????? int ?k1? = ? 24 ;
???????????? int ?k2? = ? 5 ;

???????????? int ?r1? = ?year? % ? 19 ;
???????????? int ?r2? = ?year? % ? 4 ;
???????????? int ?r3? = ?year? % ? 7 ;
???????????? int ?r4? = ?( 19 ? * ?r1? + ?k1)? % ? 30 ;
???????????? int ?r5? = ?( 2 ? * ?r2? + ? 4 ? * ?r3? + ? 6 ? * ?r4? + ?k2)? % ? 7 ;
???????????? int ?A?? = ? 22 ? + ?r4? + ?r5;

???????????? if ?(A? < ? 32 )?
????????????{
????????????????month? = ? 3 ;
????????????????day? = ?A;
????????????}
???????????? else
????????????{
????????????????A? = ?r4? + ?r5? - ? 9 ;
????????????????month? = ? 4 ;
???????????????? if ?(A? == ? 26 )
????????????????????day? = ? 19 ;
???????????????? else ? if ?(A? != ? 25 )?
????????????????????day? = ?A;
???????????????? else ? if ?(r4? == ? 18 ?? && ?r5? > ? 10 )
????????????????????day? = ? 18 ;
???????????????? else
????????????????????day? = ? 25 ;
????????????}
????????????
???????????? return ? new ?DateTime(year,month,day);
????????}
????}