const int SECOND = 1;
const int MINUTE = 60 * SECOND;
const int HOUR = 60 * MINUTE;
const int DAY = 24 * HOUR;
const int MONTH = 30 * DAY;

if (delta < 0)
{
  return "not yet";
}
if (delta < 1 * MINUTE)
{
  return ts.Seconds == 1 ? "1秒前" : ts.Seconds + "秒前";
}
if (delta < 2 * MINUTE)
{
  return "1分钟之前";
}
if (delta < 45 * MINUTE)
{
  return ts.Minutes + "分钟";
}
if (delta < 90 * MINUTE)
{
  return "1小时前";
}
if (delta < 24 * HOUR)
{
  return ts.Hours + "小时前";
}
if (delta < 48 * HOUR)
{
  return "昨天";
}
if (delta < 30 * DAY)
{
  return ts.Days + " 天之前";
}
if (delta < 12 * MONTH)
{
  int months = Convert.ToInt32(Math.Floor((double)ts.Days / 30));
  return months <= 1 ? "一个月之前" : months + "月之前";
}
else
{
  int years = Convert.ToInt32(Math.Floor((double)ts.Days / 365));
  return years <= 1 ? "一年前" : years + "年前";
}