Asp.NET時間Since変換

public static string Since(System.DateTime now, System.DateTime last)
{
    string strResult = "";

    try
    {
        TimeSpan ts = new TimeSpan();
        ts = now.Subtract(last);
        string strNumber = "";

        if (ts.TotalSeconds <= 30)
        {
            //30   
            strResult = "  ";
        }
        else if (ts.TotalSeconds <= 59)
        {
            //  1  
            strResult = "1   ";
        }
        else if (ts.TotalMinutes <= 60 && ts.TotalMinutes != 30)
        {
            //  ，    30    
            strNumber = Convert.ToInt32(ts.TotalMinutes).ToString();
            if (ts.TotalMinutes == 2)
            {
                strNumber = " ";
            }

            strResult = strNumber + "   ";
        }
        else if (ts.TotalMinutes == 30)
        {
            //    
            strResult = "    ";
        }
        else if (ts.TotalHours <= 23)
        {
            //  
            strNumber = Convert.ToInt32(ts.TotalHours).ToString();
            if (ts.TotalHours == 2)
            {
                strNumber = " ";
            }

            strResult = ts.Hours + "   ";
        }
        else if (ts.TotalHours == 24)
        {
            //    
            strResult = "   ";
        }
        else if (ts.TotalDays < 30 && ts.TotalDays != 15)
        {
            //     
            strNumber = Convert.ToInt32(ts.TotalDays).ToString();
            if (ts.TotalDays == 2)
            {
                strNumber = " ";
            }

            strResult = strNumber + "  ";
        }
        else if (ts.TotalDays == 15)
        {
            //  
            strResult = "    ";
        }
        else if (ts.TotalDays <= 364)
        {
            //   
            int month = Convert.ToInt32(ts.TotalDays) / 30;
            strNumber = month.ToString();
            if (month == 2)
            {
                strNumber = " ";
            }
            strResult = strNumber + "   ";
        }
        else if (ts.TotalDays <= 547)
        {
            //      
            strResult = "   ";
        }
        else if (ts.TotalDays <= 910)
        {
            //      
            strResult = "   ";
        }
        else
        {
            strResult = last.ToString("yy M d ");
        }
    }
    catch (Exception ex)
    {
        YtRuntime.WriteLog(ex.ToString());
        strResult = last.ToString("yy M d ");
    }
    return strResult;
}

public static string Since(System.DateTime last)
{
    return Since(System.DateTime.Now, last);
}