/* luaload.c
 *
 * Kamil Kaminski
 * kkaminsk.com
 *
 * Loading a Lua table in C
 *
 *
 */

#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct platform
{
    unsigned int xres_w;
    unsigned int yres_w;
    unsigned int bpp_w;
    float fovy_w;
    float znear_w;
    float zfar_w;
};

const char *LuaGetFieldString(lua_State *L, const char *);
double luaGetFieldNumber(lua_State *, const char *);
int luaLoadConfig(lua_State *, const char *);
int luaFillPlatform(lua_State *, struct platform *);
void printPlatform(struct platform *);

const char *LuaGetFieldString(lua_State *L, const char *key)
{
    if (!L || !key)
        return NULL;

    const char *ret = NULL;

    /* push the key string onto stack */
    lua_pushstring(L, key);

    lua_gettable(L, -2);
    if (!lua_isstring(L, -1))
    {
        fprintf(stderr, "Lua: \"%s\" field within the table is not a string\n", key);
        lua_pop(L, 1);

        return ret;
    }

    ret = lua_tostring(L, -1);
    lua_pop(L, 1);

    return ret;
}

double luaGetFieldNumber(lua_State *L, const char *key)
{
    if (!L || !key)
        return -1.0;

    double ret = -1.0;

    /* push the key string onto stack */
    lua_pushstring(L, key);

    /* remember, -1 points to top of the stack, our table should a second
     * item from the top, this call effectively accesses t[key] and
     * pushes that value on the stack */
    lua_gettable(L, -2);
    if (!lua_isnumber(L, -1))
    {
        fprintf(stderr, "Lua: \"%s\" field within the table is NaN\n", key);
        lua_pop(L, 1);

        return ret;
    }

    /* finally retrieve our value */
    ret = lua_tonumber(L, -1);

    /* value is no longer needed, pop it */
    lua_pop(L, 1);

    return ret;
}

int luaLoadConfig(lua_State *L, const char *fname)
{
    if (!L || !fname)
        return -1;

    int status;

    /* load the file containing the config */
    /* call a function, what function? dry run the script? */
    status = (luaL_loadfile(L, fname) || lua_pcall(L, 0, 0, 0));
    if (status)
    {
        fprintf(stderr, "Lua: %s\n", lua_tostring(L, -1));
        return -1;
    }

    return 0;
}

int luaFillPlatform(lua_State *L, struct platform *p)
{
    if (!L || !p)
        return -1;

    double ret;

    /* pushes the table on the stack */
    lua_getglobal(L, "platform");

    if (!lua_istable(L, -1))
    {
        fprintf(stderr, "Lua: failed to parse \"platform\" table\n");
        lua_pop(L, 1);
        return -1;
    }

    if ((ret = luaGetFieldNumber(L, "xres_w")) != -1.0)
        p->xres_w  = (unsigned int) ret;

    if ((ret = luaGetFieldNumber(L, "yres_w")) != -1.0)
        p->yres_w  = (unsigned int) ret;

    if ((ret = luaGetFieldNumber(L, "bpp_w")) != -1.0)
        p->bpp_w   = (unsigned int) ret;

    if ((ret = luaGetFieldNumber(L, "fovy_w")) != -1.0)
        p->fovy_w  = (float) ret;

    if ((ret = luaGetFieldNumber(L, "znear_w")) != -1.0)
        p->znear_w = (float) ret;

    if ((ret = luaGetFieldNumber(L, "zfar_w")) != -1.0)
        p->zfar_w  = (float) ret;

    /* pop the table */
    lua_pop(L, 1);

    return 0;
}

void printPlatform(struct platform *p)
{
    if (!p)
        return;

    printf("xres_w : %u\n"
           "yres_w : %u\n"
           "bpp_w  : %u\n"
           "fovy_w : %f\n"
           "znear_w: %f\n"
           "zfar_w : %f",
           p->xres_w, p->yres_w, p->bpp_w, p->fovy_w,
           p->znear_w, p->zfar_w);
    puts("");
}

int main(int argc, char **argv)
{
    lua_State *L;

    /* create new lua state */
    L = luaL_newstate();

    /* load lua libraries */
    luaL_openlibs(L);

    struct platform p;
    memset(&p, 0, sizeof(p));
    luaLoadConfig(L, "config.lua");
    luaFillPlatform(L, &p);
    printPlatform(&p);

    lua_close(L);

    return 0;
}