Q:

Get the dates for GetWeekOfYear in c#?

I have this function which gives me ( for a current date ) - its week num :
so for  : DateTime(2009,1,1)
 CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(new DateTime(2009,1,1), CalendarWeekRule.FirstDay, DayOfWeek.Sunday).Dump();

answer : 1
and for   : DateTime(2009,1,4)
answer : 2

now  , I need a function which gives me the startDate && endDate for this values  :
so for week #1 -> 1/1/2009   ---> 1/3/2009
so for week #2 -> 1/4/2009   ---> 1/10/2009

Hence : i have a function which gives me the week num for a specified date.
but this week spans from x---> y
I need those x and y.
thanks.
p.s. - i've been searching for a func like this , and didn't find . :-(

A:

To get the first day in the week, by date:
static DateTime GetFirstDayOfWeek(DateTime date)
{
    var firstDayOfWeek = date.AddDays(-((date.DayOfWeek - DayOfWeek.Sunday + 7) % 7));
    if (firstDayOfWeek.Year != date.Year)
        firstDayOfWeek = new DateTime(date.Year, 1, 1);
    return firstDayOfWeek;
}

The last day of the week works the same way:
static DateTime GetLastDayOfWeek(DateTime date)
{
    var lastDayOfWeek = date.AddDays((DayOfWeek.Saturday - date.DayOfWeek + 7) % 7);
    if (lastDayOfWeek.Year != date.Year)
        lastDayOfWeek = new DateTime(date.Year, 12, 31);
    return lastDayOfWeek;
}

Royi's addition ( final) :
extension method which gives you all the details ( week details) from a single date :
p.s. first day of week = sunday. 
   public class DateTimeSpan
    {
        public DateTime WeekStartDate;
        public DateTime WeekEndDate;
        public DateTime MonthStartDate;
        public DateTime MonthEndDate;
        public DateTime YearStartDate;
        public DateTime YearEndDate;
        public int WeekNum;

    }

    public static DateTimeSpan TimeProperties(this DateTime str)
    {
        if (str == null) return null;
        DateTimeSpan dts = new DateTimeSpan();
        dts.WeekNum=     CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(str, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
        dts.WeekStartDate = GetFirstDayOfWeek(str);
        dts.WeekEndDate = GetLAstDayOfWeek(str);
        dts.MonthStartDate = new DateTime(str.Year, str.Month, 1);
        int numberOfDays = DateTime.DaysInMonth(str.Year, str.Month);
        DateTime last = new DateTime(str.Year, str.Month, numberOfDays);
        dts.MonthEndDate = last;
        dts.YearStartDate = new DateTime(str.Year, 1, 1);
        numberOfDays = DateTime.DaysInMonth(str.Year, 12);
        last = new DateTime(str.Year, 12, numberOfDays);
        dts.YearEndDate = last;

        return dts;
    }

    static DateTime GetFirstDayOfWeek(DateTime date)
    {
        var firstDayOfWeek = date.AddDays(-((date.DayOfWeek - DayOfWeek.Sunday + 7) % 7));
        if (firstDayOfWeek.Year != date.Year)
            firstDayOfWeek = new DateTime(date.Year, 1, 1);
        return firstDayOfWeek;
    }

    static DateTime GetLAstDayOfWeek(DateTime date)
    {
        var firstDayOfWeek = date.AddDays(((DayOfWeek.Saturday - date.DayOfWeek + 7) % 7));
        if (firstDayOfWeek.Year != date.Year)
            firstDayOfWeek = new DateTime(date.Year, 12, 31);
        return firstDayOfWeek;
    }

