#include <stdio.h>
#include <SDL.h>
#ifdef __MINGW32__
// mingw has its nanosleep implementation in pthread.h for some reson
#include <pthread.h>
#else
#include <unistd.h>
#include <time.h>
#endif

#include "gfx_window_manager_api.h"
#include "gfx_screen_config.h"

#define GFX_BACKEND_NAME "SDL"

static SDL_Window* wnd;
static SDL_GLContext ctx;
static SDL_Renderer* renderer;
static int sdl_to_lus_table[512];
static bool vsync_enabled = true;
// OTRTODO: These are redundant. Info can be queried from SDL.
static int window_width = DESIRED_SCREEN_WIDTH;
static int window_height = DESIRED_SCREEN_HEIGHT;
static bool fullscreen_state;
static bool is_running = true;
static void (*on_fullscreen_changed_callback)(bool is_now_fullscreen);

static uint64_t previous_time;

static int target_fps = 120; // above 60 since vsync is enabled by default

static uint64_t qpc_freq;

#define FRAME_INTERVAL_US_NUMERATOR 1000000
#define FRAME_INTERVAL_US_DENOMINATOR (target_fps)

static void set_fullscreen(bool on, bool call_callback) {
    if (fullscreen_state == on) {
        return;
    }
    fullscreen_state = on;
    SDL_SetWindowFullscreen(wnd, on ? SDL_WINDOW_FULLSCREEN_DESKTOP : 0);
    if (call_callback && on_fullscreen_changed_callback) {
        on_fullscreen_changed_callback(on);
    }
}

static void gfx_sdl_get_active_window_refresh_rate(uint32_t* refresh_rate) {
    int display_in_use = SDL_GetWindowDisplayIndex(wnd);

    SDL_DisplayMode mode;
    SDL_GetCurrentDisplayMode(display_in_use, &mode);
    *refresh_rate = mode.refresh_rate;
}

static inline void do_sleep(const uint64_t ns) {
    const timespec spec = { 0, ns };
    nanosleep(&spec, nullptr);
}

static void gfx_sdl_init(const char* game_name, const char* gfx_api_name, bool start_in_fullscreen, uint32_t width,
                         uint32_t height, int32_t posX, int32_t posY) {
    window_width = width;
    window_height = height;

    SDL_Init(SDL_INIT_VIDEO);

    SDL_EventState(SDL_DROPFILE, SDL_ENABLE);

    bool use_opengl = true;

    if (use_opengl) {
        SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
        SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    }

    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_COMPATIBILITY);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_DEBUG_FLAG);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);

    char title[512];
    int len = sprintf(title, "%s (%s)", game_name, gfx_api_name);

    Uint32 flags = SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;

    if (use_opengl) {
        flags = flags | SDL_WINDOW_OPENGL;
    } else {
        flags = flags | SDL_WINDOW_METAL;
    }

    int display_in_use = SDL_GetWindowDisplayIndex(wnd);
    if (display_in_use < 0) { // Fallback to default if out of bounds
        posX = 100;
        posY = 100;
    }

    wnd = SDL_CreateWindow(title, posX, posY, window_width, window_height, flags);

    if (use_opengl) {
        ctx = SDL_GL_CreateContext(wnd);
        SDL_GL_MakeCurrent(wnd, ctx);
        SDL_GL_SetSwapInterval(1);
    }

    qpc_freq = SDL_GetPerformanceFrequency();

    set_fullscreen(start_in_fullscreen, false);
}

static void gfx_sdl_close(void) {
    is_running = false;
}

static void gfx_sdl_set_fullscreen_changed_callback(void (*on_fullscreen_changed)(bool is_now_fullscreen)) {
    on_fullscreen_changed_callback = on_fullscreen_changed;
}

static void gfx_sdl_set_fullscreen(bool enable) {
    set_fullscreen(enable, true);
}

static void gfx_sdl_set_cursor_visibility(bool visible) {
    if (visible) {
        SDL_ShowCursor(SDL_ENABLE);
    } else {
        SDL_ShowCursor(SDL_DISABLE);
    }
}

static void gfx_sdl_get_dimensions(uint32_t* width, uint32_t* height, int32_t* posX, int32_t* posY) {
    SDL_GL_GetDrawableSize(wnd, static_cast<int*>((void*)width), static_cast<int*>((void*)height));
    SDL_GetWindowPosition(wnd, static_cast<int*>(posX), static_cast<int*>(posY));
}

static void gfx_sdl_handle_events(void) {
    SDL_Event event;
    while (SDL_PollEvent(&event)) {
        switch (event.type) {
            case SDL_KEYDOWN:
                if (event.key.keysym.sym == SDLK_RETURN && (event.key.keysym.mod & KMOD_ALT)) {
                    // alt-enter received, switch fullscreen state
                    set_fullscreen(!fullscreen_state, true);
                }
                break;
            case SDL_WINDOWEVENT:
                if (event.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
                    SDL_GL_GetDrawableSize(wnd, &window_width, &window_height);
                } else if (event.window.event == SDL_WINDOWEVENT_CLOSE &&
                           event.window.windowID == SDL_GetWindowID(wnd)) {
                    // We listen specifically for main window close because closing main window
                    // on macOS does not trigger SDL_Quit.
                    exit(0);
                }
                break;
            case SDL_QUIT:
                exit(0);
                break;
        }
    }
}

static bool gfx_sdl_start_frame(void) {
    return true;
}

static uint64_t qpc_to_100ns(uint64_t qpc) {
    return qpc / qpc_freq * 10000000 + qpc % qpc_freq * 10000000 / qpc_freq;
}

static inline void sync_framerate_with_timer(void) {
    uint64_t t;
    t = qpc_to_100ns(SDL_GetPerformanceCounter());

    const int64_t next = previous_time + 10 * FRAME_INTERVAL_US_NUMERATOR / FRAME_INTERVAL_US_DENOMINATOR;
    const int64_t left = next - t;
    if (left > 0) {
        do_sleep(left * 100);
    }

    t = qpc_to_100ns(SDL_GetPerformanceCounter());
    if (left > 0 && t - next < 10000) {
        // In case it takes some time for the application to wake up after sleep,
        // or inaccurate timer,
        // don't let that slow down the framerate.
        t = next;
    }
    previous_time = t;
}

static void gfx_sdl_swap_buffers_begin(void) {
    if (target_fps) {
        sync_framerate_with_timer();
    }
    SDL_GL_SwapWindow(wnd);
}

static void gfx_sdl_swap_buffers_end(void) {

}

static double gfx_sdl_get_time(void) {
    return SDL_GetPerformanceCounter() / (double)qpc_freq;
}

static void gfx_sdl_set_target_fps(int fps) {
    target_fps = fps;
}

static bool gfx_sdl_can_disable_vsync(void) {
    return false;
}

static void *gfx_sdl_get_window_handle(void) {
    return (void *)wnd;
}

static void gfx_sdl_set_window_title(const char *title) {
    SDL_SetWindowTitle(wnd, title);
}

static void gfx_sdl_set_swap_interval(int interval) {
    SDL_GL_SetSwapInterval(interval);
    vsync_enabled = (interval != 0);
}

struct GfxWindowManagerAPI gfx_sdl = { 
    gfx_sdl_init,
    gfx_sdl_close,
    gfx_sdl_set_fullscreen_changed_callback,
    gfx_sdl_set_fullscreen,
    gfx_sdl_get_active_window_refresh_rate,
    gfx_sdl_set_cursor_visibility,
    gfx_sdl_get_dimensions,
    gfx_sdl_handle_events,
    gfx_sdl_start_frame,
    gfx_sdl_swap_buffers_begin,
    gfx_sdl_swap_buffers_end,
    gfx_sdl_get_time,
    gfx_sdl_set_target_fps,
    gfx_sdl_can_disable_vsync,
    gfx_sdl_get_window_handle,
    gfx_sdl_set_window_title,
    gfx_sdl_set_swap_interval,
};