// gcc -Wall -Wextra -pedantic -Wno-unused-parameter -std=c11 kruzhochek.c -luser32 -lgdi32 -o kruzhochek.exe

#define STRICT
#define UNICODE
#define WIN32_LEAN_AND_MEAN
#define _WIN32_WINNT 0x501
#include <windows.h>

static void window_create(HWND hWnd)
{
    HDC dc = GetDC(hWnd);

    // По-хорошему, после SelectObject нужно старые объекты бережно хранить и
    // восстанавливать, но окна собственный DC (CS_OWNDS), а приложение все
    // равно закрывается после закрытия окна, поэтому ничего никуда не утекает.

    HBRUSH brush = CreateSolidBrush(RGB(20, 80, 100));
    SelectObject(dc, brush);

    HPEN pen = CreatePen(PS_SOLID, 8, RGB(200, 40, 40));
    SelectObject(dc, pen);

    HFONT font = CreateFont(-100, 0, 0, 0, FW_DONTCARE, FALSE, FALSE, FALSE,
        DEFAULT_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY,
        DEFAULT_PITCH, TEXT("Comic Sans MS"));
    SelectObject(dc, font);

    SetTextColor(dc, RGB(240, 240, 240));
    SetBkMode(dc, TRANSPARENT);
}

static void window_paint(HWND hWnd)
{
    RECT rect;
    GetClientRect(hWnd, &rect);

    // У клиентской областии left/top всегда нули
    const int width = rect.right;
    const int height = rect.bottom;
    const int radius = 200;
    const int center_x = width / 2;
    const int center_y = height / 2;

    PAINTSTRUCT ps;

    BeginPaint(hWnd, &ps);
        const HDC dc = ps.hdc;

        BeginPath(dc);
        Arc(dc, center_x - radius, center_y - radius, center_x + radius, center_y + radius,
            center_x, center_y, center_x, center_y);
        EndPath(dc);
        StrokeAndFillPath(dc);

        MoveToEx(dc, 0, 0, NULL);
        LineTo(dc, width, height);
        MoveToEx(dc, rect.right, 0, NULL);
        LineTo(dc, 0, height);

        DrawText(dc, TEXT("sup /pr/"), -1, &rect, DT_CENTER | DT_VCENTER | DT_SINGLELINE);
    EndPaint(hWnd, &ps);
}

// Дальше обычный бойлерплейт для винды.

static LRESULT CALLBACK window_proc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg) {
        case WM_CREATE:
            window_create(hWnd);
            return 0;

        case WM_PAINT:
            window_paint(hWnd);
            return 0;

        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;

        default:
            break;
    }

    return DefWindowProc(hWnd, uMsg, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASS wc = {
        .style = CS_OWNDC | CS_SAVEBITS | CS_HREDRAW | CS_VREDRAW,
        .lpfnWndProc = window_proc,
        .hInstance = hInstance,
        .hIcon = LoadIcon(NULL, IDI_APPLICATION),
        .hCursor = LoadCursor(NULL, IDC_ARROW),
        .hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH),
        .lpszClassName = TEXT("gdi_graphics"),
    };

    if (!RegisterClass(&wc)) {
        MessageBox(NULL, TEXT("RegisterClass() failed!"), TEXT("Error"), MB_ICONERROR);
        return 1;
    }

    HWND hWnd = CreateWindowEx(0, wc.lpszClassName, TEXT("GDI Graphics"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 600, 600, NULL, NULL, hInstance, NULL);

    if (!hWnd) {
        MessageBox(NULL, TEXT("CreateWindowEx() failed!"), TEXT("Error"), MB_ICONERROR);
        return 2;
    }

    ShowWindow(hWnd, nCmdShow);
    UpdateWindow(hWnd);

    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam; // nExitCode от PostQuitMessage.
}