Best Extension Methods: Date and Time

Best Extension Methods for Date and time

public static class DateExtensions
{

    /// 

    /// DateDiff in SQL style. 
    /// Datepart implemented: 
    ///     "year" (abbr. "yy", "yyyy"), 
    ///     "quarter" (abbr. "qq", "q"), 
    ///     "month" (abbr. "mm", "m"), 
    ///     "day" (abbr. "dd", "d"), 
    ///     "week" (abbr. "wk", "ww"), 
    ///     "hour" (abbr. "hh"), 
    ///     "minute" (abbr. "mi", "n"), 
    ///     "second" (abbr. "ss", "s"), 
    ///     "millisecond" (abbr. "ms").
    /// 
    /// 
    /// 
    /// 
    public static Int64 DateDiff(this DateTime StartDate, String DatePart, DateTime EndDate)
    {
        Int64 DateDiffVal = 0;
        System.Globalization.Calendar cal = System.Threading.Thread.CurrentThread.CurrentCulture.Calendar;
        TimeSpan ts = new TimeSpan(EndDate.Ticks - StartDate.Ticks);
        switch (DatePart.ToLower().Trim())
        {
            #region year
            case "year":
            case "yy":
            case "yyyy":
                DateDiffVal = (Int64)(cal.GetYear(EndDate) - cal.GetYear(StartDate));
                break;
            #endregion

            #region quarter
            case "quarter":
            case "qq":
            case "q":
                DateDiffVal = (Int64)((((cal.GetYear(EndDate)
                                    - cal.GetYear(StartDate)) * 4)
                                    + ((cal.GetMonth(EndDate) - 1) / 3))
                                    - ((cal.GetMonth(StartDate) - 1) / 3));
                break;
            #endregion

            #region month
            case "month":
            case "mm":
            case "m":
                DateDiffVal = (Int64)(((cal.GetYear(EndDate)
                                    - cal.GetYear(StartDate)) * 12
                                    + cal.GetMonth(EndDate))
                                    - cal.GetMonth(StartDate));
                break;
            #endregion

            #region day
            case "day":
            case "d":
            case "dd":
                DateDiffVal = (Int64)ts.TotalDays;
                break;
            #endregion

            #region week
            case "week":
            case "wk":
            case "ww":
                DateDiffVal = (Int64)(ts.TotalDays / 7);
                break;
            #endregion

            #region hour
            case "hour":
            case "hh":
                DateDiffVal = (Int64)ts.TotalHours;
                break;
            #endregion

            #region minute
            case "minute":
            case "mi":
            case "n":
                DateDiffVal = (Int64)ts.TotalMinutes;
                break;
            #endregion

            #region second
            case "second":
            case "ss":
            case "s":
                DateDiffVal = (Int64)ts.TotalSeconds;
                break;
            #endregion

            #region millisecond
            case "millisecond":
            case "ms":
                DateDiffVal = (Int64)ts.TotalMilliseconds;
                break;
            #endregion

            default:
                throw new Exception(String.Format("DatePart \"{0}\" is unknown", DatePart));
        }
        return DateDiffVal;
    }
    public static string ToStringDDMMYYYYFromDate(this DateTime date)
    {
        if (date == null)
        {
            return "";
        }
        else
        {
            return date.ToString("dd/MM/yyyy");

        }
    }
    public static string ToStringDDMMYYYYFromDate(this DateTime? date)
    {
        if (date == null)
        {
            return "";
        }
        else
        {
            return ((DateTime)date).ToString("dd-MM-yyyy");

        }
    }
    static public int Age(this DateTime dateOfBirth)
    {
        if (DateTime.Today.Month < dateOfBirth.Month ||
        DateTime.Today.Month == dateOfBirth.Month &&
         DateTime.Today.Day < dateOfBirth.Day)
        {
            return DateTime.Today.Year - dateOfBirth.Year - 1;
        }
        else
            return DateTime.Today.Year - dateOfBirth.Year;
    }
    public static string ToFriendlyDateString(this DateTime Date)
    {
        string FormattedDate = "";
        if (Date.Date == DateTime.Today)
        {
            FormattedDate = "Today";
        }
        else if (Date.Date == DateTime.Today.AddDays(-1))
        {
            FormattedDate = "Yesterday";
        }
        else if (Date.Date > DateTime.Today.AddDays(-6))
        {
            // *** Show the Day of the week
            FormattedDate = Date.ToString("dddd").ToString();
        }
        else
        {
            FormattedDate = Date.ToString("MMMM dd, yyyy");
        }

        //append the time portion to the output
        FormattedDate += " @ " + Date.ToString("t").ToLower();
        return FormattedDate;
    }
    public static bool IsWeekend(this DayOfWeek d)
    {
        return !d.IsWeekday();
    }

    public static bool IsWeekday(this DayOfWeek d)
    {
        switch (d)
        {
            case DayOfWeek.Sunday:
            case DayOfWeek.Saturday: return false;

            default: return true;
        }
    }

    public static DateTime AddWorkdays(this DateTime d, int days)
    {
        // start from a weekday
        while (d.DayOfWeek.IsWeekday()) d = d.AddDays(1.0);
        for (int i = 0; i < days; ++i)
        {
            d = d.AddDays(1.0);
            while (d.DayOfWeek.IsWeekday()) d = d.AddDays(1.0);
        }
        return d;
    }
    public static string FirstDayOfMonth(this DateTime date)
    {
        return new DateTime(date.Year, date.Month, 1).ToString("MM/dd/yyyy");
    }

    public static string LastDayOfMonth(this DateTime date)
    {
        return new DateTime(DateTime.Now.Year, DateTime.Now.Month + 1, 1).AddDays(-1).ToString("MM/dd/yyyy");
    }
    /// 

    /// Converts a regular DateTime to a RFC822 date string.
    /// 
    /// The specified date formatted as a RFC822 date string.
    public static string ToRFC822DateString(this DateTime date)
    {
        int offset = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now).Hours;
        string timeZone = "+" + offset.ToString().PadLeft(2, '0');
        if (offset < 0)
        {
            int i = offset * -1;
            timeZone = "-" + i.ToString().PadLeft(2, '0');
        }
        return date.ToString("ddd, dd MMM yyyy HH:mm:ss " + timeZone.PadRight(5, '0'), System.Globalization.CultureInfo.GetCultureInfo("en-US"));
    }
}

Compiled By: Rajesh Rolen