// Exercise 30.1: 
// Modify the dir_iter function in the directory example
// so that it closes the DIR structure when it reaches
// the end of the traversal.
// With this change,
// the program does not need to wait for a garbage collection
// to release a resource that it knows it will not need anymore.

// (When you close the directory,
// you should set the address stored in the userdatum to NULL,
// to signal to the finalizer that the directory is already closed.
// Also, function dir_iter will have to check whether the directory
// is not closed before using it.)

#define LUA_COMPAT_APIINTCASTS

#include <cmath>
#include <cstdint>
#include <dirent.h>
#include <exception>
#include <iomanip>
#include <iostream>
#include <limits>
#include <string>
#include <vector>
#include <stack>
#include <unordered_set>

#include "lua.hpp"

namespace {

bool AbortWithMessage(const char* message) {
    std::cout << message << std::endl;
    std::abort();
}

bool LoadFile(lua_State* state, const std::string& filename) {
    return !(luaL_loadfile(state, filename.c_str()) || lua_pcall(state, 0, 0, 0));
}

int dir_iter(lua_State *L) {
    DIR** dir_ptr = (DIR**) lua_touserdata(L, lua_upvalueindex(1));

    struct dirent* entry;
    if (*dir_ptr && (entry = readdir(*dir_ptr)) != NULL) {
        lua_pushstring(L, entry->d_name);
        return 1;
    }

    // Directory is empty.
    if (*dir_ptr) {
        closedir(*dir_ptr);
        *dir_ptr = nullptr;
    }

    return 0;
}

int l_dir(lua_State *L) {
    const char *path = luaL_checkstring(L, 1);

    DIR** d = (DIR**) lua_newuserdata(L, sizeof(DIR*));

    luaL_getmetatable(L, "LuaBook.dir");
    lua_setmetatable(L, -2);

    *d = opendir(path);
    if (*d == NULL) {
        luaL_error(L, "cannot open %s: %s", path, strerror(errno));
    }

    lua_pushcclosure(L, dir_iter, 1);
    return 1;
}

int dir_gc(lua_State *L) {
    DIR* d = *(DIR**) lua_touserdata(L, 1);
    if (d) {
        closedir(d);
    }
    return 0;
}

const struct luaL_Reg dirlib[] = {
    {"open", l_dir},
    {NULL, NULL}
};

int luaopen_dir(lua_State *L) {
    luaL_newmetatable(L, "LuaBook.dir");

    lua_pushcfunction(L, dir_gc);
    lua_setfield(L, -2, "__gc");

    luaL_newlib(L, dirlib);
    lua_setglobal(L, "dir");
    return 0;
}

}  // namespace

int main(int argc, char* argv[]) {
    if (argc < 2) {
        std::cout << "Please, specify lua script file to run." << std::endl;
        return 0;
    }

    lua_State* L = luaL_newstate();
    luaL_openlibs(L);
    luaopen_dir(L);

    if (!LoadFile(L, std::string(argv[1]))) {
        AbortWithMessage(lua_tostring(L, -1));
        return -1;
    }

    return 0;
}