[PIU] Simple Text Editor

#include <windows.h>
#define BUFFER(x,y) *(pBuffer + y * cxBuffer + x)

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("Typer");
    HWND hwnd;
    MSG msg;
    WNDCLASS wndclass;

    wndclass.style = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc = WndProc;
    wndclass.cbClsExtra = 0;
    wndclass.cbWndExtra = 0;
    wndclass.hInstance = hInstance;
    wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName = NULL;
    wndclass.lpszClassName = szAppName;

    if (!RegisterClass(&wndclass))
    {
        MessageBox(NULL, TEXT("Nie udało się zarejestrować klasy okna!"), szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("Simple Text Editor"),
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    static DWORD dwCharSet = DEFAULT_CHARSET;
    static int cxChar, cyChar, cxClient, cyClient, cxBuffer, cyBuffer, xCaret, yCaret;
    static TCHAR * pBuffer = NULL;
    HDC hdc;
    int x, y, i;
    PAINTSTRUCT ps;
    TEXTMETRIC tm;

    switch (msg)
    {
    case WM_INPUTLANGCHANGE:
        dwCharSet = wParam;

    case WM_CREATE:
        hdc = GetDC(hwnd);
        SelectObject(hdc, CreateFont(0, 0, 0, 0, 0, 0, 0, 0, dwCharSet, 0, 0, 0, FIXED_PITCH, NULL));

        GetTextMetrics(hdc, &tm);
        cxChar = tm.tmAveCharWidth;
        cyChar = tm.tmHeight;

        DeleteObject(SelectObject(hdc, GetStockObject(SYSTEM_FONT)));
        ReleaseDC(hwnd, hdc);

    case WM_SIZE: //pobierz rozmiar okna w pikselach

        if (msg == WM_SIZE)
        {
            cxClient = LOWORD(lParam);
            cyClient = HIWORD(lParam);
        }

        cxBuffer = max(1, cxClient / cxChar);
        cyBuffer = max(1, cyClient / cyChar);

        //przydziel pamięć na bufor i wykasuj ją

        if (pBuffer != NULL)
            free(pBuffer);

        pBuffer = (TCHAR *) malloc(cxBuffer * cyBuffer * sizeof(TCHAR));

        for (y = 0; y < cyBuffer; y++)
            for (x = 0; x < cxBuffer; x++)
                BUFFER(x, y) = ' ';

        xCaret = 0;
        yCaret = 0;

        if (hwnd == GetFocus())
            SetCaretPos(xCaret * cxChar, yCaret * cyChar);

        InvalidateRect(hwnd, NULL, TRUE);
        return 0;

    case WM_SETFOCUS: //stwórz i wyświetl karetkę

        CreateCaret(hwnd, NULL, cxChar, cyChar);
        SetCaretPos(xCaret * cxChar, yCaret * cyChar);
        ShowCaret(hwnd);
        return 0;

    case WM_KILLFOCUS: // ukryj i usuń karetkę

        HideCaret(hwnd);
        DestroyCaret();
        return 0;

    case WM_KEYDOWN:
        switch (wParam)
        {
        case VK_HOME:
            xCaret = 0;
            break;

        case VK_END:
            xCaret = cxBuffer - 1;
            break;

        case VK_PRIOR:
            yCaret = 0;
            break;

        case VK_NEXT:
            yCaret = cyBuffer - 1;
            break;

        case VK_LEFT:
            yCaret = max(xCaret - 1, 0);
            break;

        case VK_RIGHT:
            xCaret = max(xCaret + 1, cxBuffer - 1);
            break;

        case VK_UP:
            yCaret = max(yCaret - 1, 0);
            break;

        case VK_DOWN:
            yCaret = min(yCaret + 1, cyBuffer - 1);
            break;

        case VK_DELETE:
            for (x = xCaret; x < cxBuffer - 1; x++)
                BUFFER(x, yCaret) = BUFFER(x + 1, yCaret);

            BUFFER(cxBuffer - 1, yCaret) = ' ';

            HideCaret(hwnd);
            hdc = GetDC(hwnd);

            SelectObject(hdc, CreateFont(0, 0, 0, 0, 0, 0, 0, 0, dwCharSet, 0, 0, 0, FIXED_PITCH, NULL));

            TextOut(hdc, xCaret * cxChar, yCaret *cyChar, &BUFFER(xCaret, yCaret), cxBuffer - xCaret);

            DeleteObject(SelectObject(hdc, GetStockObject(SYSTEM_FONT)));
            ReleaseDC(hwnd, hdc);
            ShowCaret(hwnd);
            break;
        }

        SetCaretPos(xCaret * cxChar, yCaret * cyChar);
        return 0;

    case WM_CHAR:
        for (i = 0; i < (int)LOWORD(lParam); i++)
        {
            switch (wParam)
            {
            case '\b': //backspace
                if (xCaret > 0)
                {
                    xCaret--;
                    SendMessage(hwnd, WM_KEYDOWN, VK_DELETE, 1);
                }
                break;

            case '\t': // tab
                do {
                    SendMessage(hwnd, WM_CHAR, ' ', 1);
                } while (xCaret % 8 != 0);
                break;

            case '\n': //new line
                if (++yCaret == cyBuffer)
                    yCaret = 0;
                break;

            case '\r': // powrót karetki
                xCaret = 0;

                if (++yCaret == cyBuffer)
                    yCaret = 0;
                break;

            case '\x1B': //esc key
                for (y = 0; y< cyBuffer; y++)
                    for (x = 0; x< cxBuffer; x++)
                        BUFFER(x, y) = ' ';

                xCaret = 0;
                yCaret = 0;

                InvalidateRect(hwnd, NULL, FALSE);
                break;

            default:
                BUFFER(xCaret, yCaret) = (TCHAR)wParam;

                HideCaret(hwnd);
                hdc = GetDC(hwnd);

                SelectObject(hdc, CreateFont(0, 0, 0, 0, 0, 0, 0, 0, dwCharSet, 0, 0, 0, FIXED_PITCH, NULL));

                TextOut(hdc, xCaret * cxChar, yCaret * cyChar, &BUFFER(xCaret, yCaret), 1);
                DeleteObject(SelectObject(hdc, GetStockObject(SYSTEM_FONT)));
                ReleaseDC(hwnd, hdc);
                ShowCaret(hwnd);

                if (++xCaret == cxBuffer)
                {
                    xCaret = 0;

                    if (++yCaret == cyBuffer)
                        yCaret = 0;
                }
                break;
            }
        }

        SetCaretPos(xCaret * cxChar, yCaret * cyChar);
        return 0;

    case WM_PAINT:

        hdc = BeginPaint(hwnd, &ps);
        SelectObject(hdc, CreateFont(0, 0, 0, 0, 0, 0, 0, 0, dwCharSet, 0, 0, 0, FIXED_PITCH, NULL));

        for (y = 0; y< cyBuffer; y++)
            TextOut(hdc, 0, y * cyChar, &BUFFER(0, y), cxBuffer);

        DeleteObject(SelectObject(hdc, GetStockObject(SYSTEM_FONT)));
        EndPaint(hwnd, &ps);
        return 0;

    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd, msg, wParam, lParam);
}