GMail and iCloud style Date Formatting

DateExtensions.cs

 public enum TimeFormat
{
    Auto,
    IfPresent,
    Always,
    Today,
    Never
}

public static class DateExtensions
{
    const string DefaultDateFormat = "{0:MM/dd/yyyy}";
    const string DefaultDateNoYearFormat = "{0:dd MMM}";
    const string DefaultWeekDateFormat = "{0:ddd}";
    const string DefaultDateTimeFormat = "{0:dd MMM yyyy hh:mm tt}";
    const string DefaultTimeFormat = "{0:hh:mm tt}";
    
    public static DateTime GetStartOfWeek(this DateTime dateTime)
    {
      DayOfWeek day = dateTime.DayOfWeek;
      int days = day - DayOfWeek.Monday;
      return dateTime.AddDays(-days);
    }

    public static DateTime GetEndOfWeek(this DateTime dateTime)
    {
      DayOfWeek day = dateTime.DayOfWeek;
      int days = DayOfWeek.Saturday - day;
      return dateTime.AddDays(days);
    }
    
    public static string ToDisplayText(this DateTime dateTime, TimeFormat timeFormat = TimeFormat.Auto)
    {
        StringBuilder builder = new StringBuilder();
        if (DateTime.Today != dateTime.Date)
        {
            //TimeSpan elapsed = (DateTime.Now - dateTime);
            if (dateTime >= DateTime.Today.GetStartOfWeek() && dateTime <= DateTime.Today.GetEndOfWeek())
                builder.AppendFormat(DefaultWeekDateFormat, dateTime);
            else
                builder.AppendFormat(dateTime.Year == DateTime.Today.Year 
                    ? DefaultDateNoYearFormat
                    : DefaultDateFormat, dateTime);
        }

        switch (timeFormat)
        {
            case TimeFormat.Auto: // In auto mode we use the Today Logic
            case TimeFormat.Today:
                if (dateTime.Date == DateTime.Today && dateTime.TimeOfDay.TotalSeconds > 0.0)
                    goto case TimeFormat.Always;
                break;

            case TimeFormat.IfPresent:
                if (dateTime.TimeOfDay.TotalSeconds > 0.0)
                    goto case TimeFormat.Always;
                break;

            case TimeFormat.Always:
                builder.Append(' ');
                builder.AppendFormat(DefaultTimeFormat, dateTime);
                break;

            case TimeFormat.Never:
                break;
        }            
        return builder.ToString();
    }

}