lua_kernel_base.cpp

/*
   Copyright (C) 2014 by Chris Beck <render787@gmail.com>
   Part of the Battle for Wesnoth Project http://www.wesnoth.org/

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY.

   See the COPYING file for more details.
*/

#include "scripting/lua_kernel_base.hpp"

#include "global.hpp"

#include "exceptions.hpp"
#include "filesystem.hpp"
#include "game_errors.hpp"
#include "game_config.hpp" //for game_config::debug_lua
#include "log.hpp"
#include "lua/lauxlib.h"
#include "lua/lua.h"
#include "lua/lualib.h"
#include "lua/luaconf.h"                // for LUAL_BUFFERSIZE
#include "lua_jailbreak_exception.hpp"  // for tlua_jailbreak_exception
#include "map_location.hpp"

#ifdef DEBUG_LUA
#include "scripting/debug_lua.hpp"
#endif

#include "scripting/lua_api.hpp"
#include "scripting/lua_common.hpp"
#include "scripting/lua_gui2.hpp"
#include "scripting/lua_types.hpp"

#include "version.hpp"                  // for do_version_check, etc

#include <boost/bind.hpp>
#include <boost/scoped_ptr.hpp>

#include <cstring>
#include <exception>
#include <new>
#include <string>
#include <sstream>
#include <vector>

static lg::log_domain log_scripting_lua("scripting/lua");
#define DBG_LUA LOG_STREAM(debug, log_scripting_lua)
#define LOG_LUA LOG_STREAM(info, log_scripting_lua)
#define WRN_LUA LOG_STREAM(warn, log_scripting_lua)
#define ERR_LUA LOG_STREAM(err, log_scripting_lua)

// Callback implementations

/**
 * Checks if a file exists (not necessarily a Lua script).
 * - Arg 1: string containing the file name.
 * - Ret 1: boolean
 */
static int intf_have_file(lua_State *L)
{
	char const *m = luaL_checkstring(L, 1);
	std::string p = filesystem::get_wml_location(m);
	if (p.empty()) { lua_pushboolean(L, false); }
	else { lua_pushboolean(L, true); }
	return 1;
}

class lua_filestream
{
public:
	lua_filestream(const std::string& fname)
		: pistream_(filesystem::istream_file(fname))
	{

	}

	static const char * lua_read_data(lua_State * /*L*/, void *data, size_t *size)
	{
		lua_filestream* lfs = static_cast<lua_filestream*>(data);

		//int startpos = lfs->pistream_->tellg();
		lfs->pistream_->read(lfs->buff_, LUAL_BUFFERSIZE);
		//int newpos = lfs->pistream_->tellg();
		*size = lfs->pistream_->gcount();
#if 0
		ERR_LUA << "read bytes from " << startpos << " to " << newpos << " in total " *size << " from steam\n";
		ERR_LUA << "streamstate beeing "
			<< " goodbit:" << lfs->pistream_->good()
			<< " endoffile:" << lfs->pistream_->eof()
			<< " badbit:" <<  lfs->pistream_->bad()
			<< " failbit:" << lfs->pistream_->fail() << "\n";
#endif
		return lfs->buff_;
	}

	static int lua_loadfile(lua_State *L, const std::string& fname)
	{
		lua_filestream lfs(fname);
		//lua uses '@' to know that this is a file (as opposed to a something as opposed to something loaded via loadstring )
		std::string chunkname = '@' + fname;
		LOG_LUA << "starting to read from " << fname << "\n";
		return  lua_load(L, &lua_filestream::lua_read_data, &lfs, chunkname.c_str(), NULL);
	}
private:
	char buff_[LUAL_BUFFERSIZE];
	boost::scoped_ptr<std::istream> pistream_;
};

/**
 * Loads and executes a Lua file.
 * - Arg 1: string containing the file name.
 * - Ret *: values returned by executing the file body.
 */
static int intf_dofile(lua_State *L)
{
	char const *m = luaL_checkstring(L, 1);
	std::string p = filesystem::get_wml_location(m);
	if (p.empty())
		return luaL_argerror(L, 1, "file not found");

	lua_settop(L, 0);

#if 1
	try
	{
		if(lua_filestream::lua_loadfile(L, p))
			return lua_error(L);
	}
	catch(const std::exception & ex)
	{
		luaL_argerror(L, 1, ex.what());
	}
#else
	//oldcode to be deleted if newcode works
	if (luaL_loadfile(L, p.c_str()))
		return lua_error(L);
#endif

	lua_call(L, 0, LUA_MULTRET);
	return lua_gettop(L);
}


/**
 * Loads and executes a Lua file, if there is no corresponding entry in wesnoth.package.
 * Stores the result of the script in wesnoth.package and returns it.
 * - Arg 1: string containing the file name.
 * - Ret 1: value returned by the script.
 */
static int intf_require(lua_State *L)
{
	char const *m = luaL_checkstring(L, 1);

	// Check if there is already an entry.

	luaW_getglobal(L, "wesnoth", NULL);
	lua_pushstring(L, "package");
	lua_rawget(L, -2);
	lua_pushvalue(L, 1);
	lua_rawget(L, -2);
	if (!lua_isnil(L, -1) && !game_config::debug_lua) return 1;
	lua_pop(L, 1);


	std::string p = filesystem::get_wml_location(m);
	if (p.empty())
		return luaL_argerror(L, 1, "file not found");

	// Compile the file.

#if 1
	try
	{
		if(lua_filestream::lua_loadfile(L, p))
			throw game::error(lua_tostring(L, -1));
	}
	catch(const std::exception & ex)
	{
		chat_message("Lua error", ex.what());
		ERR_LUA << ex.what() << '\n';
		return 0;
	}
#else
	//oldcode to be deleted if newcode works

	int res = luaL_loadfile(L, p.c_str());
	if (res)
	{
		char const *m = lua_tostring(L, -1);
		chat_message("Lua error", m);
		ERR_LUA << m << '\n';
		return 0;
	}
#endif

	// Execute it.
	if (!luaW_pcall(L, 0, 1)) return 0;

	// Add the return value to the table.
	lua_pushvalue(L, 1);
	lua_pushvalue(L, -2);
	lua_settable(L, -4);
	return 1;
}


/**
 * Compares 2 version strings - which is newer.
 * - Args 1,3: version strings
 * - Arg 2: comparison operator (string)
 * - Ret 1: comparison result
 */
static int intf_compare_versions(lua_State* L)
{
	char const *v1 = luaL_checkstring(L, 1);

	const VERSION_COMP_OP vop = parse_version_op(luaL_checkstring(L, 2));
	if(vop == OP_INVALID) return luaL_argerror(L, 2, "unknown version comparison operator - allowed are ==, !=, <, <=, > and >=");

	char const *v2 = luaL_checkstring(L, 3);

	const bool result = do_version_check(version_info(v1), vop, version_info(v2));
	lua_pushboolean(L, result);

	return 1;
}

/**
 * Helper function which gets a map location from the stack. Handles lua (1-based) to C++ (0-based) conversion.
 * Expected: stack has at least two elements, top is y, next is x.
 */
static map_location pop_map_location(lua_State* L)
{
	if (lua_gettop(L) < 2) {
		luaL_error(L, "pop_map_location: expected to find a map location on the stack, but stack has less than two elements");
		return map_location();
	}
	int y = luaL_checkint(L, -1);
	int x = luaL_checkint(L, -2);
	lua_pop(L, 2);

	return map_location(x-1, y-1);
}

/**
 * Helper function which pushes a map location onto the stack. Handles lua (1-based) to C++ (0-based) conversion.
 */
static void push_map_location(lua_State* L, const map_location & loc)
{
	lua_pushinteger(L, loc.x+1);
	lua_pushinteger(L, loc.y+1);
}

/**
 * Expose map_location::get_direction function to lua
 */
static int intf_map_location_get_direction(lua_State* L)
{
	int nargs = lua_gettop(L);
	if (nargs != 3 and nargs != 4) {
		std::string msg("get_direction: must pass 3 or 4 args, found ");
		msg += nargs;
		luaL_error(L, msg.c_str());
		return 0;
	}

	int n = 1;
	if (nargs == 4) {
		n = luaL_checkint(L, -1);
		lua_pop(L,1);
	}

	map_location::DIRECTION d;
	if (lua_isnumber(L, -1)) {
		d = map_location::rotate_right(map_location::NORTH, luaL_checkint(L, -1)); //easiest way to correctly convert int to direction
		lua_pop(L,1);
	} else if (lua_isstring(L, -1)) {
		d = map_location::parse_direction(luaL_checkstring(L,-1));
		lua_pop(L,1);
	} else {
		std::string msg("get_direction: third argument should be a direction, either a string or an integer, instead found a ");
		msg += lua_typename(L, lua_type(L, -1));
		luaL_argerror(L, -1, msg.c_str());
		return 0;
	}

	map_location l = pop_map_location(L);
	map_location result = l.get_direction(d, n);

	push_map_location(L, result);
	return 2;
}

/**
 * Expose map_location::vector_sum to lua
 */
static int intf_map_location_vector_sum(lua_State* L)
{
	map_location l2 = pop_map_location(L);
	map_location l1 = pop_map_location(L);

	push_map_location(L, l1.vector_sum_assign(l2));
	return 2;
}

/**
 * Expose map_location::vector_negation to lua
 */
static int intf_map_location_vector_negation(lua_State* L)
{
	map_location l1 = pop_map_location(L);

	push_map_location(L, l1.vector_negation());
	return 2;
}

/**
 * Expose map_location::ZERO to lua
 */
static int intf_map_location_vector_zero(lua_State* L)
{
	push_map_location(L, map_location::ZERO());
	return 2;
}

/**
 * Expose map_location::rotate_right_around_center to lua
 */
static int intf_map_location_rotate_right_around_center(lua_State* L)
{
	int k = luaL_checkint(L, -1);
	lua_pop(L,1);
	map_location center = pop_map_location(L);
	map_location loc = pop_map_location(L);

	push_map_location(L, loc.rotate_right_around_center(center, k));
	return 2;
}

/**
 * Expose map_location tiles_adjacent
 */
static int intf_map_location_tiles_adjacent(lua_State* L)
{
	map_location l2 = pop_map_location(L);
	map_location l1 = pop_map_location(L);

	lua_pushboolean(L, tiles_adjacent(l1,l2));
	return 1;
}

/**
 * Expose map_location get_adjacent_tiles
 */
static int intf_map_location_get_adjacent_tiles(lua_State* L)
{
	map_location l1 = pop_map_location(L);

	map_location locs[6];
	get_adjacent_tiles(l1, locs);

	for (int i = 0; i < 6; ++i) {
		push_map_location(L, locs[i]);
	}

	return 12;
}

/**
 * Expose map_location distance_between
 */
static int intf_map_location_distance_between(lua_State* L)
{
	map_location l2 = pop_map_location(L);
	map_location l1 = pop_map_location(L);

	lua_pushinteger(L, distance_between(l1,l2));
	return 1;
}

/**
 * Expose map_location get_in_basis_N_NE
 */
static int intf_map_location_get_in_basis_N_NE(lua_State* L)
{
	map_location l1 = pop_map_location(L);

	std::pair<int, int> r = l1.get_in_basis_N_NE();
	lua_pushinteger(L, r.first);
	lua_pushinteger(L, r.second);
	return 2;
}

/**
 * Expose map_location get_relative_dir
 */
static int intf_map_location_get_relative_dir(lua_State* L)
{
	map_location l2 = pop_map_location(L);
	map_location l1 = pop_map_location(L);

	lua_pushinteger(L, l1.get_relative_dir(l2));
	return 1;
}

/**
 * Expose map_location parse_direction
 */
static int intf_map_location_parse_direction(lua_State* L)
{
	std::string str = luaL_checkstring(L, -1);
	map_location::DIRECTION d = map_location::parse_direction(str);
	if (d == map_location::NDIRECTIONS) {
		luaL_argerror(L, -1, "error: not a direction string");
		return 0;
	} else {
		lua_pushinteger(L, d);
		return 1;
	}
}

/**
 * Expose map_location write_direction
 */
static int intf_map_location_write_direction(lua_State* L)
{
	int d = luaL_checkint(L, -1);
	if (d >= 0 && d < map_location::NDIRECTIONS) {
		lua_pushstring(L, map_location::write_direction(static_cast<map_location::DIRECTION>(d)).c_str());
		return 1;
	} else {
		luaL_argerror(L, -1, "error: must be an integer from 0 to 5");
		return 0;
	}
}

/**
 * Replacement print function -- instead of printing to std::cout, print to the command log.
 * Intended to be bound to this' command_log at registration time.
 */
int lua_kernel_base::intf_print(lua_State* L)
{
	DBG_LUA << "intf_print called:\n";
	size_t nargs = lua_gettop(L);

	for (size_t i = 2; i <= nargs; ++i) { // ignore first argument, since it's the userdata from boost cfunc binding
		cmd_log_ << lua_tostring(L,i);
		DBG_LUA << "'" << lua_tostring(L,i) << "'\n";
	}

	cmd_log_ << "\n";
	DBG_LUA << "\n";

	lua_pop(L, nargs - 1);

	return 0;
}

// Make the possibility to push the boost::bind 'ed intf_print onto the lua stack, using a dispatcher to get around the C++ / boost::function aspect of this
char const * boost_cfunc = "Boost_C_Function";

typedef boost::function<int(lua_State*)> lua_cfunc;

static int intf_boost_cfunc_dispatcher ( lua_State* L )
{
	lua_cfunc *f = static_cast<lua_cfunc *> (lua_touserdata(L, 1));
	int result = (*f)(L);
	lua_remove(L,1);
	return result;
}

static int intf_boost_cfunc_cleanup ( lua_State* L )
{
	lua_cfunc * d = static_cast< lua_cfunc *> (luaL_testudata(L, 1, boost_cfunc));
	if (d == NULL) {
		ERR_LUA << "boost_cfunc_cleanup called on data of type: " << lua_typename( L, lua_type( L, 1 ) ) << std::endl;
		ERR_LUA << "This may indicate a memory leak, please report at bugs.wesnoth.org" << std::endl;
	} else {
		d->~lua_cfunc();
	}
	return 0;
}

static void register_boost_cfunc_metatable ( lua_State* L )
{
	luaL_newmetatable(L, boost_cfunc);
	lua_pushcfunction(L, intf_boost_cfunc_dispatcher);
	lua_setfield(L, -2, "__call");
	lua_pushcfunction(L, intf_boost_cfunc_cleanup);
	lua_setfield(L, -2, "__gc");
	lua_pushvalue(L, -1); //make a copy of this table, set it to be its own __index table
	lua_setfield(L, -2, "__index");

	lua_pop(L, 1);
}

static void push_boost_cfunc( lua_State* L, const lua_cfunc & f )
{
	void * p = lua_newuserdata(L, sizeof(lua_cfunc));
	luaL_setmetatable(L, boost_cfunc);
	new (p) lua_cfunc(f);
}

// The show-dialog call back is here implemented as a method of lua kernel, since it needs a pointer to external object CVideo
int lua_kernel_base::intf_show_dialog(lua_State *L)
{
	if (!video_) {
		ERR_LUA << "Cannot show dialog, no video object is available to this lua kernel.";
		lua_error(L);
		return 0;
	}

	return lua_gui2::show_dialog(L, *video_);
}


// End Callback implementations

lua_kernel_base::lua_kernel_base(CVideo * video)
 : mState(luaL_newstate())
 , video_(video)
 , cmd_log_()
{
	lua_State *L = mState;

	cmd_log_ << "Initializing " << my_name() << "...\n";

	// Open safe libraries.
	// Debug and OS are not, but most of their functions will be disabled below.
	cmd_log_ << "Adding standard libs...\n";

	static const luaL_Reg safe_libs[] = {
		{ "",       luaopen_base   },
		{ "table",  luaopen_table  },
		{ "string", luaopen_string },
		{ "math",   luaopen_math   },
		{ "debug",  luaopen_debug  },
		{ "os",     luaopen_os     },
		{ NULL, NULL }
	};
	for (luaL_Reg const *lib = safe_libs; lib->func; ++lib)
	{
		luaL_requiref(L, lib->name, lib->func, 1);
		lua_pop(L, 1);  /* remove lib */
	}

	// Disable functions from os which we don't want.
	lua_getglobal(L, "os");
	lua_pushnil(L);
	while(lua_next(L, -2) != 0) {
		lua_pop(L, 1);
		char const* function = lua_tostring(L, -1);
		if(strcmp(function, "clock") == 0 || strcmp(function, "date") == 0
			|| strcmp(function, "time") == 0 || strcmp(function, "difftime") == 0) continue;
		lua_pushnil(L);
		lua_setfield(L, -3, function);
	}
	lua_pop(L, 1);

	// Disable functions from debug which we don't want.
	lua_getglobal(L, "debug");
	lua_pushnil(L);
	while(lua_next(L, -2) != 0) {
		lua_pop(L, 1);
		char const* function = lua_tostring(L, -1);
		if(strcmp(function, "traceback") == 0) continue;
		lua_pushnil(L);
		lua_setfield(L, -3, function);
	}
	lua_pop(L, 1);

	// Delete dofile and loadfile.
	lua_pushnil(L);
	lua_setglobal(L, "dofile");
	lua_pushnil(L);
	lua_setglobal(L, "loadfile");

	// Store the error handler.
	cmd_log_ << "Adding error handler...\n";

	lua_pushlightuserdata(L
			, executeKey);
	lua_getglobal(L, "debug");
	lua_getfield(L, -1, "traceback");
	lua_remove(L, -2);
	lua_rawset(L, LUA_REGISTRYINDEX);
	lua_pop(L, 1);

	// Create the gettext metatable.
	cmd_log_ << "Adding gettext metatable...\n";

	lua_pushlightuserdata(L
			, gettextKey);
	lua_createtable(L, 0, 2);
	lua_pushcfunction(L, lua_common::impl_gettext);
	lua_setfield(L, -2, "__call");
	lua_pushstring(L, "message domain");
	lua_setfield(L, -2, "__metatable");
	lua_rawset(L, LUA_REGISTRYINDEX);

	// Create the tstring metatable.
	cmd_log_ << "Adding tstring metatable...\n";

	lua_pushlightuserdata(L
			, tstringKey);
	lua_createtable(L, 0, 4);
	lua_pushcfunction(L, lua_common::impl_tstring_concat);
	lua_setfield(L, -2, "__concat");
	lua_pushcfunction(L, lua_common::impl_tstring_collect);
	lua_setfield(L, -2, "__gc");
	lua_pushcfunction(L, lua_common::impl_tstring_tostring);
	lua_setfield(L, -2, "__tostring");
	lua_pushstring(L, "translatable string");
	lua_setfield(L, -2, "__metatable");
	lua_rawset(L, LUA_REGISTRYINDEX);

	lua_settop(L, 0);

	// Define the Boost_C_Function metatable ( so we can override print to point to a C++ member function )
	cmd_log_ << "Adding boost cfunc proxy...\n";

	register_boost_cfunc_metatable(L);

	// Add some callback from the wesnoth lib
	cmd_log_ << "Registering basic wesnoth API...\n";

	static luaL_Reg const callbacks[] = {
		{ "compare_versions",         &intf_compare_versions         		},
		{ "dofile",                   &intf_dofile                   		},
		{ "have_file",                &intf_have_file                		},
		{ "require",                  &intf_require                  		},
		{ "textdomain",               &lua_common::intf_textdomain   		},
		{ "get_dialog_value",         &lua_gui2::intf_get_dialog_value		},
		{ "set_dialog_active",        &lua_gui2::intf_set_dialog_active		},
		{ "set_dialog_callback",      &lua_gui2::intf_set_dialog_callback	},
		{ "set_dialog_canvas",        &lua_gui2::intf_set_dialog_canvas		},
		{ "set_dialog_markup",        &lua_gui2::intf_set_dialog_markup		},
		{ "set_dialog_value",         &lua_gui2::intf_set_dialog_value		},
		{ NULL, NULL }
	};

	lua_getglobal(L, "wesnoth");
	if (!lua_istable(L,-1)) {
		lua_newtable(L);
	}
	luaL_setfuncs(L, callbacks, 0);
	lua_setglobal(L, "wesnoth");

	// Override the print function
	cmd_log_ << "Redirecting print function...\n";

	lua_getglobal(L, "print");
	lua_setglobal(L, "std_print"); //storing original impl as 'std_print'
	lua_settop(L, 0); //clear stack, just to be sure

	lua_cfunc my_print = boost::bind(&lua_kernel_base::intf_print, this, _1);
	push_boost_cfunc(L, my_print);
	lua_setglobal(L, "print");

	// Add the show_dialog function
	cmd_log_ << "Adding dialog support...\n";

	lua_getglobal(L, "wesnoth");
	lua_cfunc show_dialog = boost::bind(&lua_kernel_base::intf_show_dialog, this, _1);
	push_boost_cfunc(L, show_dialog);
	lua_setfield(L, -2, "show_dialog");
	lua_pop(L,1);

	// Create the package table.
	lua_getglobal(L, "wesnoth");
	lua_newtable(L);
	lua_setfield(L, -2, "package");
	lua_pop(L, 1);

	// Get some callbacks for map locations
	cmd_log_ << "Adding map_location table...\n";

	static luaL_Reg const map_callbacks[] = {
		{ "get_direction",		&intf_map_location_get_direction         		},
		{ "vector_sum",			&intf_map_location_vector_sum				},
		{ "vector_negation",		&intf_map_location_vector_negation			},
		{ "zero",			&intf_map_location_vector_zero				},
		{ "rotate_right_around_center",	&intf_map_location_rotate_right_around_center		},
		{ "tiles_adjacent",		&intf_map_location_tiles_adjacent			},
		{ "get_adjacent_tiles",		&intf_map_location_get_adjacent_tiles			},
		{ "distance_between",		&intf_map_location_distance_between			},
		{ "get_in_basis_N_NE",		&intf_map_location_get_in_basis_N_NE			},
		{ "get_relative_dir",		&intf_map_location_get_relative_dir			},
		{ "parse_direction",		&intf_map_location_parse_direction			},
		{ "write_direction",		&intf_map_location_write_direction			},
		{ NULL, NULL }
	};

	// Create the map_location table.
	lua_getglobal(L, "wesnoth");
	lua_newtable(L);
	luaL_setfuncs(L, map_callbacks, 0);
	lua_setfield(L, -2, "map_location");
	lua_pop(L,1);
}

lua_kernel_base::~lua_kernel_base()
{
	lua_close(mState);
}

void lua_kernel_base::log_error(char const * msg, char const * context)
{
	ERR_LUA << context << ": " << msg;
}

void lua_kernel_base::throw_exception(char const * msg, char const * context)
{
	throw game::lua_error(msg, context);
}

bool lua_kernel_base::protected_call(int nArgs, int nRets)
{
	error_handler eh = boost::bind(&lua_kernel_base::log_error, this, _1, _2 );
	return protected_call(nArgs, nRets, eh);
}

bool lua_kernel_base::load_string(char const * prog)
{
	error_handler eh = boost::bind(&lua_kernel_base::log_error, this, _1, _2 );
	return load_string(prog, eh);
}

bool lua_kernel_base::protected_call(int nArgs, int nRets, error_handler e_h)
{
	lua_State *L = mState;

	// Load the error handler before the function and its arguments.
	lua_pushlightuserdata(L
			, executeKey);

	lua_rawget(L, LUA_REGISTRYINDEX);
	lua_insert(L, -2 - nArgs);

	int error_handler_index = lua_gettop(L) - nArgs - 1;

	// Call the function.
	int errcode = lua_pcall(L, nArgs, nRets, -2 - nArgs);
	tlua_jailbreak_exception::rethrow();

	// Remove the error handler.
	lua_remove(L, error_handler_index);

	if (errcode != LUA_OK) {
		std::string message = lua_tostring(L, -1);

		std::string context = "When executing, ";
		if (errcode == LUA_ERRRUN) {
			context += "Lua runtime error";
		} else if (errcode == LUA_ERRERR) {
			context += "Lua error in attached debugger";
		} else if (errcode == LUA_ERRMEM) {
			context += "Lua out of memory error";
		} else if (errcode == LUA_ERRGCMM) {
			context += "Lua error in garbage collection metamethod";
		} else {
			context += "unknown lua error";
		}

		lua_pop(mState, 1);

		e_h(message.c_str(), context.c_str());

		return false;
	}

	return true;
}

bool lua_kernel_base::load_string(char const * prog, error_handler e_h)
{
	int errcode = luaL_loadstring(mState, prog);
	if (errcode != LUA_OK) {
		std::string msg = lua_tostring(mState, -1);

		std::string context = "When parsing a string to lua, ";

		if (errcode == LUA_ERRSYNTAX) {
			context += " a syntax error";
		} else if(errcode == LUA_ERRMEM){
			context += " a memory error";
		} else if(errcode == LUA_ERRGCMM) {
			context += " an error in garbage collection metamethod";
		} else {
			context += " an unknown error";
		}

		lua_pop(mState, 1);

		e_h(msg.c_str(), context.c_str());

		return false;
	}
	return true;
}

// Call load_string and protected call. Make them throw exceptions.
// 
void lua_kernel_base::throwing_run(const char * prog) {
	cmd_log_ << "$ " << prog << "\n";
	error_handler eh = boost::bind(&lua_kernel_base::throw_exception, this, _1, _2 );
	load_string(prog, eh);
	protected_call(0, 0, eh);
}

// Do a throwing run, but if we catch a lua_error, reformat it with signature for this function and log it.
void lua_kernel_base::run(const char * prog) {
	try {
		throwing_run(prog);
	} catch (game::lua_error & e) {
		cmd_log_ << e.what() << "\n";
		lua_kernel_base::log_error(e.what(), "In function lua_kernel::run()");
	}
}



/**
 * Loads the "package" package into the Lua environment.
 * This action is inherently unsafe, as Lua scripts will now be able to
 * load C libraries on their own, hence granting them the same privileges
 * as the Wesnoth binary itsef.
 */
void lua_kernel_base::load_package()
{
	lua_State *L = mState;
	lua_pushcfunction(L, luaopen_package);
	lua_pushstring(L, "package");
	lua_call(L, 1, 0);
}

/**
 * Gets all the global variable names in the Lua environment. This is useful for tab completion.
 */
std::vector<std::string> lua_kernel_base::get_global_var_names()
{
	std::vector<std::string> ret;

	lua_State *L = mState;

	int idx = lua_gettop(L);
	lua_getglobal(L, "_G");
	lua_pushnil(L);
	
	while (lua_next(L, idx+1) != 0) {
		if (lua_isstring(L, -2)) {
			ret.push_back(lua_tostring(L,-2));
		}
		lua_pop(L,1);
	}
	lua_settop(L, idx);
	return ret;
}

/**
 * Gets all attribute names of an extended variable name. This is useful for tab completion.
 */
std::vector<std::string> lua_kernel_base::get_attribute_names(const std::string & input)
{
	std::vector<std::string> ret;
	std::string var_path = input; // it's convenient to make a copy, even if it's a little slower

	lua_State *L = mState;

	int base = lua_gettop(L);
	lua_getglobal(L, "_G");

	size_t idx = var_path.find('.');
	size_t last_dot = 0;
	while (idx != std::string::npos ) {
		last_dot += idx + 1; // Since idx was not npos, add it to the "last_dot" idx, so that last_dot keeps track of indices in input string
		lua_pushstring(L, var_path.substr(0, idx).c_str()); //push the part of the path up to the period
		lua_rawget(L, -2);

		if (!lua_istable(L,-1) && !lua_isuserdata(L,-1)) {
			return ret; //if we didn't get a table or userdata we can't proceed
		}

		var_path = var_path.substr(idx+1); // chop off the part of the path we just dereferenced		
		idx = var_path.find('.'); // find the next .
	}
	
	std::string prefix = input.substr(0, last_dot);

	lua_pushnil(L);
	while (lua_next(L, -2) != 0) {
		if (lua_isstring(L, -2)) {
			ret.push_back(prefix + lua_tostring(L,-2));
		}
		lua_pop(L,1);
	}
	lua_settop(L, base);
	return ret;
}