Lua (approx) elapsed Time calculation

elapsed.lua

function elapsed (datestring)
  local pattern = "(%d+)-(%d+)-(%d+)T(%d+):(%d+):(%d+)Z"
  local year,month,day,hour,min,sec = datestring:match(pattern)
  local start = os.time({year = year, month = month, day = day, hour = hour, min = min, sec = sec, isdst = false })
  local utcnow = os.time(os.date("!*t"))
  local diff = utcnow-start
  local years = math.floor(diff / 31557600)
  local remainder = diff % 31557600
  local months = math.floor(remainder / 2629800)
  local remainder = diff % 2629800
  local days = math.floor(remainder / 86400)
  local remainder = diff % 86400
  local hours = math.floor(remainder / 3600)
  local remainder = diff % 3600
  local mins = math.floor(remainder / 60)
  local rval = ""
  if years > 0 then
    rval = rval..pluralize(years, "year").." "
  end
  if months > 0 then
    rval = rval..pluralize(months, "month").." "
  end
  if days > 0 then
    rval = rval..pluralize(days, "day").." "
  end
  if hours > 0 then
    rval = rval..pluralize(hours,"hour").." and "..pluralize(mins,"minute")
  else
    rval = rval..pluralize(mins,"minute")
  end
  return rval
end