-- xml.lua
-- (c) Dirk Laurie 2012   Licence: zlib/pnglib
-- That means you can do anything except claim I didn't write it.
-- Some code borrowed from `strict.lua`

--[[
Usage: 

interactive:     lua -l "xml" -i
or filter:       lua -l xml -e 'print(load("return "..io.read"*a")())'
or programming:  require "xml"

After that, you can write XMLinLua, e.g. the expression

   macro {name="author-short", 
     names{variable="author",'name form="short"'} }

represents the following string:

<macro name="author-short">
  <names variable="author">
    <name form="short"/>
  </names>
</macro>   

How it works:

  When an unknown name is encountered, an immediately available
  function is created that can be called in two ways: 
    name(body)
    name{param=val,param=val...,body}
  where `body` evaluates to a string.  If `body` does not match
  the pattern "<.*>", it will be formatted by "<%s/>".
  These will respectively be rendered in XML as 
    <name> body </name>
    <name param="val" param="val"...> body </name>
  Of course, the sequence of `param="val"` terms does not follow
  the original, since the argument is a table.

If you have already defined the name, assign `nil` to it before
trying to use it in this way. 
--]]

local getinfo, error, rawset, rawget = debug.getinfo, error, rawset, rawget

local mt = getmetatable(_G)
if mt == nil then
  mt = {}
  setmetatable(_G, mt)
end

local function what ()
  local d = getinfo(3, "S")
  return d and d.what or "C"
end

local concat=table.concat 
local format, match, gsub =string.format, string.match, string.gsub

mt.__index = function (t, n)
  if what() ~= "C" then
    local f = function(arg)   
       local body, restore    
       if type(arg)=="table" then body=arg[1]; restore=body; arg[1]=nil
       elseif type(arg)=="string" then body=arg; arg={} 
       else error("bad argument #1 to n: expected table or string, got "..
          type(arg))
       end
       if type(body)=="string" then
          if not match(body,"<.*>") then body=format("<%s/>",body) end
       else 
          arg[1]=restore
          error("bad argument to "..n..": expected string, got "..type(body))
       end
       local args={}
       for k,v in pairs(arg) do args[#args+1]=format(' %s="%s"',k,v) end
       return format("<%s%s>\n  %s\n</%s>",n,concat(args),
          gsub(body,"\n","\n  "),n)
    end
    rawset(t, n, f)
    return f
  end
end