--[[
空想具現化プログラミング
http://hammm.blog21.fc2.com/
http://hammm.dw.land.to/lua/

documentation by silica as 冬物語の人
http://winter.sgv417.jp/

[Lua] 暗黙のグローバル変数定義を抑制する方法
http://hammm.blog21.fc2.com/blog-entry-8.html
[Lua] 明示的グローバル変数宣言モジュール
http://hammm.blog21.fc2.com/blog-entry-13.html

-- 特徴
-- 以下のようにグローバル変数を明示的に宣言できます。 
global "myvar"

-- 以下の関数を記述すると「グローバル変数定義抑制」が有効になります。
use_explicit_globals()

-- 定義方法
global("変数名",値)
global "変数名"

-- モジュール未使用

このモジュールを使って組んだコードをこのモジュールを使わないで動かす場合、以下のような宣言をすれば問題なく動きます。

function global() end
function use_explicit_globals() end
function use_implicit_globals() end

----------- example ------------
require "explicit_globals"
use_explicit_globals(true) -- メインチャンクでも明示的な宣言を行う

--- OK case
global "my_global_variable"
my_global_variable = 1
local a = my_global_variable

--- NG case
my_undeclared_variable = 1 -- NG
local a = my_undeclared_variable2 -- NG

--- functions declarations
function undeclared_global_func() end  --- ok
undeclared_global_func2 = function() end  --- ok

function test()
  global "my_global_func"
  function my_global_func() end --- ok

  function undeclared_global_func3() end  --- NG
end
test()
--]]
---- explicit_globals.lua ---

-- table for global var declaration checking
local gdef = {}
local gdef_enabled = nil

-- the function to define global vars
function global(n, v)
  if not gdef_enabled then
    error("calling function global() when explicit-globals not enabled",2)
  end
  if gdef[n] == true then
    error("re-definition of global \"" .. tostring(n) .. "\"",2)
  end
  rawset(_G, n, v)
  gdef[n] = true
  
  return
end

local function registerglobal(t,n,v)
  gdef[n] = true
  rawset(t,n,v)
end

-- forbid implicit definition of global vars
function use_explicit_globals( is_explicit_in_main_chunk )

  -- set metatable for gloval environment
  local mt = getmetatable(_G)
  if mt == nil then
    mt = {}
    setmetatable(_G, mt)
  end

  -- include implicitly-declared globals in gdef table, 
  -- in case some of it becomes nil and __index,__newindex be called.
  -- drawback: if the value is nil now, it will not be included.
  for k,v in pairs(_G) do
    gdef[k] = true
  end

  mt.__newindex = function (t,n,v)
    if gdef[n] ~= nil then -- declared global
      rawset(t,n,v);return
    end
    local upfuncinfo = debug.getinfo(2,"S")
    if upfuncinfo == nil then
      registerglobal(t,n,v);return
    end
    local w = upfuncinfo.what
    if w == "C" then -- in C chunk
      registerglobal(t,n,v);return
    end
    if ( not is_explicit_in_main_chunk and w == "main" ) then -- in main chunk
      registerglobal(t,n,v);return
    end
    if type(v) == "function" then
      -- funtcion value
      if w == "main" then 
        -- declatration of functions in main chunk is ok.
        registerglobal(t,n,v);return
      else
        error("assignment of undeclared global function \"" .. tostring(n) .. "\" outside of main chunk. use global(\"var\", val)", 2)
      end
    else
      -- not function value
      error("assignment of undeclared global \"" .. tostring(n) .. "\". use global(\"var\", val)", 2)
    end
  end
  mt.__index = function (t,n)
    local upfuncinfo = debug.getinfo(2,"S")
    if gdef[n] == nil and upfuncinfo ~= nil and upfuncinfo.what ~= "C" then
      error("attempt to use undeclared global \"" .. tostring(n) .. "\". use global(\"var\", val)", 2)
    end
    return rawget(t, n)
  end
  gdef_enabled = true
end

-- back to normal, implicit global declaration.
function use_implicit_globals()
  local mt = getmetatable(_G)
  if mt ~= nil then
    mt.__newindex = nil
    mt.__index = nil
  end
  gdef_enabled = nil
end

use_explicit_globals( true ) -- use explicit globals from start, except main chunk