#include <cassert>

#define SDL_MAIN_HANDLED
#include <SDL2/SDL.h>

SDL_Rect clientArea;

SDL_HitTestResult MyHitTest(SDL_Window* win, const SDL_Point* area, void* data) {
    int w=0, h = 0;
    SDL_GetWindowSize(win, &w, &h);

    int borderWidth = 5;

    // Top
    if (area->y < borderWidth) {
        // Corners
        if (area->x < borderWidth)
            return SDL_HITTEST_RESIZE_TOPLEFT;
        else if (area->x >= w - borderWidth)
            return SDL_HITTEST_RESIZE_TOPRIGHT;
        return SDL_HITTEST_RESIZE_TOP;
    }

    // Bottom
    else if (area->y >= h - borderWidth) {
        // Corners
        if (area->x < borderWidth)
            return SDL_HITTEST_RESIZE_BOTTOMLEFT;
        else if (area->x >= w - borderWidth)
            return SDL_HITTEST_RESIZE_BOTTOMRIGHT;
        return SDL_HITTEST_RESIZE_BOTTOM;
    }

    // Left
    else if (area->x < borderWidth) {
        return SDL_HITTEST_RESIZE_LEFT;
    }

    // Right
    else if (area->x >= w - borderWidth) {
        return SDL_HITTEST_RESIZE_RIGHT;
    }

    // Drag the title bar
    else if (area->y < clientArea.y) {
        return SDL_HITTEST_DRAGGABLE;
    }

    // Cursor is in the client area
    return SDL_HITTEST_NORMAL;
}

int main() {
    assert(0 == SDL_Init(SDL_INIT_VIDEO));

    SDL_Window *window = SDL_CreateWindow(
            "HelloSDL",
            SDL_WINDOWPOS_CENTERED,
            SDL_WINDOWPOS_CENTERED,
            800,
            600,
            SDL_WINDOW_SHOWN | SDL_WINDOW_BORDERLESS
            | SDL_WINDOW_RESIZABLE
    );
    assert(window);

    SDL_Renderer *renderer = SDL_CreateRenderer(
            window,
            -1,
            SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC
    );
    assert(renderer);

    clientArea.x = 5;
    clientArea.y = 30;
    clientArea.w = 800 - 10;
    clientArea.h = 600 - 35;

    SDL_SetWindowHitTest(window, MyHitTest, nullptr);
    // The resizable flag doesn't work (?)
    SDL_SetWindowResizable(window, SDL_TRUE);

    SDL_Event event;
    do {
        SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 0xFF);
        SDL_RenderClear(renderer);
        SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
        SDL_RenderFillRect(renderer, &clientArea);
        SDL_RenderPresent(renderer);

        SDL_WaitEvent(&event);
        if (event.type == SDL_WINDOWEVENT && event.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
            clientArea.w = event.window.data1 - 10;
            clientArea.h = event.window.data2 - 35;
        }
    } while (event.type != SDL_QUIT);

    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}