#include <stdio.h> // for fprintf()
#include <stdlib.h> // for exit()

#include <SDL3/SDL.h>
#include <SDL3/SDL_main.h> // only include this one in the source file with main()!

#define INITIAL_FPS 60

SDL_Window* window = NULL;
SDL_Renderer* renderer = NULL;

static double FPS = INITIAL_FPS;
static double FrameTime = 1.0 / INITIAL_FPS;

static double PerformancePeriod;

static void panic ( const char *text ) __attribute__((noreturn));

static double GetTime()
{
    return PerformancePeriod * SDL_GetPerformanceCounter();
}

static void SetTitle(SDL_Window * window)
{
    char title[48] = {0};
    SDL_snprintf(title, sizeof(title), "Crude frame limiter @ %6.3f Hz", FPS);
    SDL_SetWindowTitle(window, title);
}

void panic ( const char *text )
{
    fprintf(stderr, "ERROR: %s. %s\n", text, SDL_GetError());
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    exit(1);
}

int main( int argc, char* argv[] )
{
    const int WIDTH = 640;
    const int HEIGHT = 480;
    int delay_threshold = 2;
    double sleep_time;
    double time_counter = 0;
    bool loopShouldStop = false;

    SDL_SetHint(SDL_HINT_RENDER_VSYNC, 0);

    if (!SDL_Init(SDL_INIT_VIDEO))
    {
        panic("SDL_Init failed");
    }

    PerformancePeriod = 1.0 / SDL_GetPerformanceFrequency();
    time_counter = GetTime();

    window = SDL_CreateWindow("Hello SDL", WIDTH, HEIGHT, SDL_WINDOW_OPENGL);
    if (!window)
    {
        panic("SDL_CreateWindow");
    }

    renderer = SDL_CreateRenderer(window, "opengl");
    if (!renderer)
    {
        panic("SDL_CreateRenderer");
    }

    //SDL_GetWindowSize(window, &width, &height);
    SetTitle(window);

    //if (!SDL_SetRenderVSync(renderer, 1))
    //{
    //    panic("SDL_SetRenderVSync");
    //}

    SDL_HideCursor();

    int red = 0;
    int green = 0;
    while (!loopShouldStop)
    {
        SDL_Event e;
        SDL_zero(e);
        while (SDL_PollEvent(&e))
        {
            if (e.type == SDL_EVENT_QUIT)
                loopShouldStop = true;
            else if (e.type == SDL_EVENT_KEY_DOWN)
            {
                if (e.key.key == SDLK_X)
                {
                    FPS -= 0.1;
                    if (FPS < 1)
                    {
                        FPS = 1;
                    }
                    FrameTime = 1.0 / FPS;
                    SetTitle(window);
                }
                else if (e.key.key == SDLK_C)
                {
                    FPS += 0.1;
                    FrameTime = 1.0 / FPS;
                    SetTitle(window);
                }
            }
            else if (e.key.mod == SDL_KMOD_LCTRL && e.key.key == SDLK_Q)
                loopShouldStop = true;
        }

        SDL_SetRenderDrawColor(renderer, red, green, 0, 255);
        SDL_RenderClear(renderer);

        sleep_time = time_counter - GetTime();
        if (sleep_time * 1000 > delay_threshold)
        {
            Uint32 ms = (Uint32)(sleep_time * 1000) - delay_threshold;
            SDL_Delay(ms);
            if (time_counter < GetTime())
            {
                delay_threshold++;
                SDL_Log("Slept too long. Increased threshold to %u ms.", delay_threshold);
            }
        }

        while (time_counter > GetTime()) {
            /* Waiting for the right moment. */
        }

        SDL_RenderPresent(renderer);
        red = (red + 1) % 256;
        green = (green + 1) % 64;

        time_counter += FrameTime;
    }
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    exit(0);
}