User:GreenC/software/base62.lua

!/usr/bin/lua

-- Given a Webcite ID on arg[1], return dates in mdy|dmy|iso|ymd format -- example ID: 6H8pdR68H

-- http://convertxy.com/index.php/numberbases/ -- http://www.onlineconversion.com/unix_time.htm

--[[--------------------------< base62 >-----------------------

    Convert base-62 to base-10
    Credit: https://de.wikipedia.org/wiki/Modul:Expr

]]

local function base62( value )

   local r = 1

   if value:match( "^%w+$" ) then
       local n = #value
       local k = 1
       local c
       r = 0
       for i = n, 1, -1 do
           c = value:byte( i, i )
           if c >= 48  and  c <= 57 then
               c = c - 48
           elseif c >= 65  and  c <= 90 then
               c = c - 55
           elseif c >= 97  and  c <= 122 then
               c = c - 61
           else    -- How comes?
               r = 1
               break    -- for i
           end
           r = r + c * k
           k = k * 62
       end -- for i
   end
   return r

end

local function main()

 -- "!" in os.date means use GMT

 zday = os.date("!%d", string.sub(string.format("%d", base62(arg[1])),1,10) )
 day = zday:match("0*(%d+)")                                                             -- remove leading zero
 zmonth = os.date("!%m", string.sub(string.format("%d", base62(arg[1])),1,10) )
 month = zmonth:match("0*(%d+)")
 nmonth = os.date("!%B", string.sub(string.format("%d", base62(arg[1])),1,10) ) 
 year = os.date("!%Y", string.sub(string.format("%d", base62(arg[1])),1,10) )

 mdy = nmonth .. " " .. day .. ", " .. year
 dmy = day .. " " .. nmonth .. " " .. year
 iso = year .. "-" .. zmonth .. "-" .. zday
 ymd = year .. " " .. nmonth .. " " .. day

 year = tonumber(year)
 month = tonumber(month)
 day = tonumber(day)

 if year < 1970 or year > 2020 then
   print "error"
 elseif day < 1 or day > 31 then
   print "error"
 elseif month < 1 or month > 12 then
   print "error"
 else
   print(mdy .. "|" .. dmy .. "|" .. iso .. "|" .. ymd)
 end

end

main()