#include <math.h>
#include "lua.h"
#include "lauxlib.h"

/* get value of Integer userdata or Lua number at index, or die */
static int checkint (lua_State *L, int index) {
   if (lua_isuserdata(L, index) && luaL_checkudata(L, index, "integer")) {
      return *(int*)lua_touserdata(L, index);
   } else if (lua_isnumber(L, index)) {
      return lua_tonumber(L, index);
   } else {
      lua_pushstring(L, "Invalid operand. Expected 'integer' or 'number'");
      lua_error(L);
      return 0; /* will never get here */
   }
}

static int create_integer(lua_State* L, int val) {
   int* ud = lua_newuserdata(L, sizeof(int));
   *ud = val;
   luaL_getmetatable(L, "integer");
   lua_setmetatable(L, -2);
   return 1;
}

static int int_new (lua_State* L) { return create_integer( L, checkint(L,1) ); }
static int int_add (lua_State* L) { return create_integer( L, checkint(L,1) + checkint(L,2) ); }
static int int_sub (lua_State* L) { return create_integer( L, checkint(L,1) - checkint(L,2) ); }
static int int_mul (lua_State* L) { return create_integer( L, checkint(L,1) * checkint(L,2) ); }
static int int_div (lua_State* L) { return create_integer( L, checkint(L,1) / checkint(L,2) ); }
static int int_mod (lua_State* L) { return create_integer( L, checkint(L,1) % checkint(L,2) ); }
static int int_pow (lua_State* L) { return create_integer( L, pow( checkint(L,1), checkint(L,2) ) ); }
static int int_unm (lua_State* L) { return create_integer( L, -checkint(L,1) ); }
static int int_eq  (lua_State* L) { lua_pushboolean( L, checkint(L,1) == checkint(L,2) ); return 1; }
static int int_lt  (lua_State* L) { lua_pushboolean( L, checkint(L,1) <  checkint(L,2) ); return 1; }
static int int_le  (lua_State* L) { lua_pushboolean( L, checkint(L,1) <= checkint(L,2) ); return 1; }
static int int_tostring (lua_State* L) {
   lua_pushnumber(L, checkint(L,1));
   lua_tostring(L, -1);
   return 1;
}

int __declspec(dllexport) __cdecl luaopen_integer (lua_State* L) {
   static const struct luaL_reg integermt[] = {
      { "__add", int_add },
      { "__sub", int_sub },
      { "__mul", int_mul },
      { "__div", int_div },
      { "__mod", int_mod },
      { "__pow", int_pow },
      { "__unm", int_unm },
      { "__eq",  int_eq  },
      { "__lt",  int_lt  },
      { "__le",  int_le  },
      { "__tostring", int_tostring},
      NULL, NULL
   };
   luaL_newmetatable(L, "integer");
   luaL_openlib(L, NULL, integermt, 0);

   lua_register(L, "int", int_new);

   return 0;
}