#include "luaincl.h"

    template <typename T> class Lunar {
      typedef struct { T *pT; } userdataType;
    public:
      typedef int (T::*mfp)(lua_State *L);
      typedef struct { const char *name; mfp mfunc; } RegType;

      static void Register(lua_State *L) {
        lua_newtable(L);
        int methods = lua_gettop(L);

        luaL_newmetatable(L, T::className);
        int metatable = lua_gettop(L);

        // store method table in globals so that
        // scripts can add functions written in Lua.
        lua_pushvalue(L, methods);
        set(L, LUA_GLOBALSINDEX, T::className);

        // hide metatable from Lua getmetatable()
        lua_pushvalue(L, methods);
        set(L, metatable, "__metatable");

        lua_pushvalue(L, methods);
        set(L, metatable, "__index");

        lua_pushcfunction(L, tostring_T);
        set(L, metatable, "__tostring");

        lua_pushcfunction(L, gc_T);
        set(L, metatable, "__gc");

        lua_newtable(L);                // mt for method table
        lua_pushcfunction(L, new_T);
        lua_pushvalue(L, -1);           // dup new_T function
        set(L, methods, "new");         // add new_T to method table
        set(L, -3, "__call");           // mt.__call = new_T
        lua_setmetatable(L, methods);

        // fill method table with methods from class T
        for (RegType *l = T::methods; l->name; l++) {
          lua_pushstring(L, l->name);
          lua_pushlightuserdata(L, (void*)l);
          lua_pushcclosure(L, thunk, 1);
          lua_settable(L, methods);
        }

        lua_pop(L, 2);  // drop metatable and method table
      }

      // call named lua method from userdata method table
      static int call(lua_State *L, const char *method,
                      int nargs=0, int nresults=LUA_MULTRET, int errfunc=0)
      {
        int base = lua_gettop(L) - nargs;  // userdata index
        if (!luaL_checkudata(L, base, T::className)) {
          lua_settop(L, base-1);           // drop userdata and args
          lua_pushfstring(L, "not a valid %s userdata", T::className);
          return -1;
        }

        lua_pushstring(L, method);         // method name
        lua_gettable(L, base);             // get method from userdata
        if (lua_isnil(L, -1)) {            // no method?
          lua_settop(L, base-1);           // drop userdata and args
          lua_pushfstring(L, "%s missing method '%s'", T::className, method);
          return -1;
        }
        lua_insert(L, base);               // put method under userdata, args

        int status = lua_pcall(L, 1+nargs, nresults, errfunc);  // call method
        if (status) {
          const char *msg = lua_tostring(L, -1);
          if (msg == NULL) msg = "(error with no message)";
          lua_pushfstring(L, "%s:%s status = %d\n%s",
                          T::className, method, status, msg);
          lua_remove(L, base);             // remove old message
          return -1;
        }
        return lua_gettop(L) - base + 1;   // number of results
      }

      // push onto the Lua stack a userdata containing a pointer to T object
      static int push(lua_State *L, T *obj, bool gc=false) {
        if (!obj) { lua_pushnil(L); return 0; }
        luaL_getmetatable(L, T::className);  // lookup metatable in Lua registry
        if (lua_isnil(L, -1)) luaL_error(L, "%s missing metatable", T::className);
        int mt = lua_gettop(L);
        subtable(L, mt, "userdata", "v");
        userdataType *ud =
          static_cast<userdataType*>(pushuserdata(L, obj, sizeof(userdataType)));
        if (ud) {
          ud->pT = obj;  // store pointer to object in userdata
          lua_pushvalue(L, mt);
          lua_setmetatable(L, -2);
          if (gc == false) {
            lua_checkstack(L, 3);
            subtable(L, mt, "do not trash", "k");
            lua_pushvalue(L, -2);
            lua_pushboolean(L, 1);
            lua_settable(L, -3);
            lua_pop(L, 1);
          }
        }
        lua_replace(L, mt);
        lua_settop(L, mt);
        return mt;  // index of userdata containing pointer to T object
      }

      // get userdata from Lua stack and return pointer to T object
      static T *check(lua_State *L, int narg) {
        userdataType *ud =
          static_cast<userdataType*>(luaL_checkudata(L, narg, T::className));
        if(!ud) luaL_typerror(L, narg, T::className);
        return ud->pT;  // pointer to T object
      }

    private:
      Lunar();  // hide default constructor

      // member function dispatcher
      static int thunk(lua_State *L) {
        // stack has userdata, followed by method args
        T *obj = check(L, 1);  // get 'self', or if you prefer, 'this'
        lua_remove(L, 1);  // remove self so member function args start at index 1
        // get member function from upvalue
        RegType *l = static_cast<RegType*>(lua_touserdata(L, lua_upvalueindex(1)));
        return (obj->*(l->mfunc))(L);  // call member function
      }

      // create a new T object and
      // push onto the Lua stack a userdata containing a pointer to T object
      static int new_T(lua_State *L) {
        lua_remove(L, 1);   // use classname:new(), instead of classname.new()
        T *obj = new T(L);  // call constructor for T objects
        push(L, obj, true); // gc_T will delete this object
        return 1;           // userdata containing pointer to T object
      }

      // garbage collection metamethod
      static int gc_T(lua_State *L) {
        if (luaL_getmetafield(L, 1, "do not trash")) {
          lua_pushvalue(L, 1);  // dup userdata
          lua_gettable(L, -2);
          if (!lua_isnil(L, -1)) return 0;  // do not delete object
        }
        userdataType *ud = static_cast<userdataType*>(lua_touserdata(L, 1));
        T *obj = ud->pT;
        if (obj) delete obj;  // call destructor for T objects
        return 0;
      }

      static int tostring_T (lua_State *L) {
        char buff[32];
        userdataType *ud = static_cast<userdataType*>(lua_touserdata(L, 1));
        T *obj = ud->pT;
        sprintf(buff, "%p", obj);
        lua_pushfstring(L, "%s (%s)", T::className, buff);
        return 1;
      }

      static void set(lua_State *L, int table_index, const char *key) {
        lua_pushstring(L, key);
        lua_insert(L, -2);  // swap value and key
        lua_settable(L, table_index);
      }

      static void weaktable(lua_State *L, const char *mode) {
        lua_newtable(L);
        lua_pushvalue(L, -1);  // table is its own metatable
        lua_setmetatable(L, -2);
        lua_pushliteral(L, "__mode");
        lua_pushstring(L, mode);
        lua_settable(L, -3);   // metatable.__mode = mode
      }

      static void subtable(lua_State *L, int tindex, const char *name, const char *mode) {
        lua_pushstring(L, name);
        lua_gettable(L, tindex);
        if (lua_isnil(L, -1)) {
          lua_pop(L, 1);
          lua_checkstack(L, 3);
          weaktable(L, mode);
          lua_pushstring(L, name);
          lua_pushvalue(L, -2);
          lua_settable(L, tindex);
        }
      }

      static void *pushuserdata(lua_State *L, void *key, size_t sz) {
        void *ud = 0;
        lua_pushlightuserdata(L, key);
        lua_gettable(L, -2);     // lookup[key]
        if (lua_isnil(L, -1)) {
          lua_pop(L, 1);         // drop nil
          lua_checkstack(L, 3);
          ud = lua_newuserdata(L, sz);  // create new userdata
          lua_pushlightuserdata(L, key);
          lua_pushvalue(L, -2);  // dup userdata
          lua_settable(L, -4);   // lookup[key] = userdata
        }
        return ud;
      }
    };