init.lua

-- No guests mod.
-- By VanessaE, sfan5, and kaeza.

local disallowed = {
   ["guest"]            =   "Guest accounts are disallowed on this server.  "..
                        "Please choose a proper username and try again.",
   ["[4a]dm[1il]n"]      =   "That is a clearly false, misleading, or otherwise disallowed username. "..
                        "Please choose a unique username and try again.",
   ["^[0-9]+$"]         =   "All-numeric usernames are disallowed on this server. "..
                        "Please choose a proper username and try again.",
   ["[0-9].-[0-9].-[0-9].-[0-9].-[0-9]"]   =   "Too many numbers in your username. "..
                                    "Please try again with less than five digits in your username.",
   ["^[A-Za-z]+[0-9][0-9][0-9]+$"] = "Please choice your own username. Usernames with letters then 3 or more digits are not allowed"
}

-- Original implementation (in Python) by sfan5
local function judge(msg)
   local numspeakable = 0
   local numnotspeakable = 0
   local cn = 0
   local lastc = '____'
   for c in msg:gmatch(".") do
      c = c:lower()
      if c:find("[aeiou0-9_-]") then
         if cn > 2 and not c:find("[0-9]") then
            numnotspeakable = numnotspeakable + 1
         elseif not c:find("[0-9]") then
            numspeakable = numspeakable + 1
         end
         cn = 0
      else
         if (cn == 1) and (lastc == c) and (lastc ~= 's') then
            numnotspeakable = numnotspeakable + 1
            cn = 0
         end
         if cn > 2 then
            numnotspeakable = numnotspeakable + 1
            cn = 0
         end
         if lastc:find("[aeiou]") then
            numspeakable = numspeakable + 1
            cn = 0
         end
         if not ((lastc:find("[aipfom]") and c == "r") or (lastc == "c" and c == "h")) then
            cn = cn + 1
         end
      end
      lastc = c
   end
   if cn > 0 then
      numnotspeakable = numnotspeakable + 1
   end
   return (numspeakable >= numnotspeakable)
end

minetest.register_on_prejoinplayer(function(name, ip)
   if not minetest.player_exists(name) then
      local lname = name:lower()
      for re, reason in pairs(disallowed) do
         if lname:find(re) then
            return reason
         end
      end

      if #name < 2 then
         return "Too short of a username. "..
               "Please pick a name with at least two letters and try again."
      end

      if not judge(name) and #name > 5 then
         return "Your username just plain looks like gibberish. "..
               "Please pick something readable and try again."
      end
   end
end)