日期和时间处理的类库

　　发一个专门处理时间和日期的类库，记录以备查询。

using System;

namespace Utilities
{
    /// <summary>
    /// Common DateTime Methods.
    /// </summary>
    /// 
    public enum Quarter
    {
        First = 1,
        Second = 2,
        Third = 3,
        Fourth = 4
    }

    public enum Month
    {
        January = 1,
        February = 2,
        March = 3,
        April = 4,
        May = 5,
        June = 6,
        July = 7,
        August = 8,
        September = 9,
        October = 10,
        November = 11,
        December = 12
    }

    public class DateUtilities
    {
        #region Quarter

        public static DateTime GetStartOfQuarter( int Year, Quarter Qtr )
        {
            if( Qtr == Quarter.First )    // 1st Quarter = January 1 to March 31
                return new DateTime( Year, 1, 1, 0, 0, 0, 0 );
            else if( Qtr == Quarter.Second ) // 2nd Quarter = April 1 to June 30
                return new DateTime( Year, 4, 1, 0, 0, 0, 0 );
            else if( Qtr == Quarter.Third ) // 3rd Quarter = July 1 to September 30
                return new DateTime( Year, 7, 1, 0, 0, 0, 0 );
            else // 4th Quarter = October 1 to December 31
                return new DateTime( Year, 10, 1, 0, 0, 0, 0 );
        }

        public static DateTime GetEndOfQuarter( int Year, Quarter Qtr )
        {
            if( Qtr == Quarter.First )    // 1st Quarter = January 1 to March 31
                return new DateTime( Year, 3, DateTime.DaysInMonth( Year, 3 ), 23, 59, 59, 999 );
            else if( Qtr == Quarter.Second ) // 2nd Quarter = April 1 to June 30
                return new DateTime( Year, 6, DateTime.DaysInMonth( Year, 6 ), 23, 59, 59, 999 );
            else if( Qtr == Quarter.Third ) // 3rd Quarter = July 1 to September 30
                return new DateTime( Year, 9, DateTime.DaysInMonth( Year, 9 ), 23, 59, 59, 999 );
            else // 4th Quarter = October 1 to December 31
                return new DateTime( Year, 12, DateTime.DaysInMonth( Year, 12 ), 23, 59, 59, 999 );
        }
        
        public static Quarter GetQuarter( Month month )
        {
            if( month <= Month.March )    // 1st Quarter = January 1 to March 31
                return Quarter.First;
            else if( ( month >= Month.April ) && ( month <= Month.June ) ) // 2nd Quarter = April 1 to June 30
                return Quarter.Second;
            else if( ( month >= Month.July ) && ( month <= Month.September ) ) // 3rd Quarter = July 1 to September 30
                return Quarter.Third;
            else // 4th Quarter = October 1 to December 31
                return Quarter.Fourth;
        }

        public static DateTime GetEndOfLastQuarter()
        {            
            if( DateTime.Now.Month <= (int)Month.March ) //go to last quarter of previous year
                return GetEndOfQuarter( DateTime.Now.Year - 1, GetQuarter( Month.December ));
            else //return last quarter of current year
                return GetEndOfQuarter( DateTime.Now.Year, GetQuarter( (Month)DateTime.Now.Month));
        }

        public static DateTime GetStartOfLastQuarter()
        {
            if( DateTime.Now.Month <= 3 ) //go to last quarter of previous year
                return GetStartOfQuarter( DateTime.Now.Year - 1, GetQuarter( Month.December ));
            else //return last quarter of current year
                return GetStartOfQuarter( DateTime.Now.Year, GetQuarter( (Month)DateTime.Now.Month));
        }

        public static DateTime GetStartOfCurrentQuarter()
        {
            return GetStartOfQuarter( DateTime.Now.Year, GetQuarter( (Month)DateTime.Now.Month ));
        }

        public static DateTime GetEndOfCurrentQuarter()
        {
            return GetEndOfQuarter( DateTime.Now.Year, GetQuarter( (Month)DateTime.Now.Month ));
        }
        #endregion

        #region Weeks
        public static DateTime GetStartOfLastWeek()
        {
            int DaysToSubtract = (int)DateTime.Now.DayOfWeek + 7;
            DateTime dt = DateTime.Now.Subtract( System.TimeSpan.FromDays( DaysToSubtract ) );
            return new DateTime( dt.Year, dt.Month, dt.Day, 0, 0, 0, 0 );
        }

        public static DateTime GetEndOfLastWeek()
        {
            DateTime dt = GetStartOfLastWeek().AddDays(6);
            return new DateTime( dt.Year, dt.Month, dt.Day, 23, 59, 59, 999 );
        }

        public static DateTime GetStartOfCurrentWeek()
        {
            int DaysToSubtract = (int)DateTime.Now.DayOfWeek ;
            DateTime dt = DateTime.Now.Subtract( System.TimeSpan.FromDays( DaysToSubtract ) );
            return new DateTime( dt.Year, dt.Month, dt.Day, 0, 0, 0, 0 );
        }

        public static DateTime GetEndOfCurrentWeek()
        {
            DateTime dt = GetStartOfCurrentWeek().AddDays(6);
            return new DateTime( dt.Year, dt.Month, dt.Day, 23, 59, 59, 999 );
        }
        #endregion

        #region Months

        public static DateTime GetStartOfMonth( int Month, int Year )
        {
            return new DateTime( Year, Month, 1, 0, 0, 0, 0 );
        }

        public static DateTime GetEndOfMonth( int Month, int Year )
        {
            return new DateTime( Year, Month, DateTime.DaysInMonth( Year, Month ), 23, 59, 59, 999 );
        }

        public static DateTime GetStartOfLastMonth()
        {
            if( DateTime.Now.Month == 1 )
                return GetStartOfMonth( 12, DateTime.Now.Year - 1);
            else
                return GetStartOfMonth( DateTime.Now.Month -1, DateTime.Now.Year );            
        }

        public static DateTime GetEndOfLastMonth()
        {
            if( DateTime.Now.Month == 1 )
                return GetEndOfMonth( 12, DateTime.Now.Year - 1);
            else
                return GetEndOfMonth( DateTime.Now.Month -1, DateTime.Now.Year );
        }

        public static DateTime GetStartOfCurrentMonth()
        {
            return GetStartOfMonth( DateTime.Now.Month, DateTime.Now.Year );
        }

        public static DateTime GetEndOfCurrentMonth()
        {
            return GetEndOfMonth( DateTime.Now.Month, DateTime.Now.Year );
        }
        #endregion

        #region Years
        public static DateTime GetStartOfYear( int Year )
        {
            return new DateTime( Year, 1, 1, 0, 0, 0, 0 );
        }

        public static DateTime GetEndOfYear( int Year )
        {
            return new DateTime( Year, 12, DateTime.DaysInMonth( Year, 12 ), 23, 59, 59, 999 );
        }

        public static DateTime GetStartOfLastYear()
        {
            return GetStartOfYear( DateTime.Now.Year - 1 );
        }

        public static DateTime GetEndOfLastYear()
        {
            return GetEndOfYear( DateTime.Now.Year - 1 );
        }

        public static DateTime GetStartOfCurrentYear()
        {
            return GetStartOfYear( DateTime.Now.Year );
        }

        public static DateTime GetEndOfCurrentYear()
        {
            return GetEndOfYear( DateTime.Now.Year );
        }
        #endregion        

        #region Days

        public static DateTime GetStartOfDay( DateTime date )
        {
            return new DateTime( date.Year, date.Month, date.Day, 0, 0, 0, 0 );
        }

        public static DateTime GetEndOfDay( DateTime date )
        {
            return new DateTime( date.Year, date.Month, date.Day, 23, 59, 59, 999 );
        }

        #endregion
    }
}