wm_char

#define WIN32_LEAN_AND_MEAN
#define _CRT_SECURE_NO_WARNINGS
#define _SCL_SECURE_NO_WARNINGS

#include <Windows.h>
#include <cstdio>
#include <utility>
#include <string>
#include <vector>

struct TextEdit {
    std::wstring buffer;
    int caret = 0;

    wchar_t const* Buffer() {
        return buffer.data();
    }

    int Length() {
        return buffer.size();
    }

    void NormalizeCaret() {
        if (caret < 0) {
            caret = 0;
        } else if (caret > Length()) {
            caret = buffer.size();
        }
    }

    void Insert(wchar_t ch) {
        NormalizeCaret();
        buffer.insert(caret, 1, ch);
        caret += 1;
    }

    void Insert(std::wstring const& str) {
        NormalizeCaret();
        if (!str.empty()) {
            buffer.insert(caret, str);
            caret += str.size();
        }
    }

    void EraseLeft() {
        NormalizeCaret();
        if (caret > 0) {
            buffer.erase(caret - 1, 1);
            caret -= 1;
        }
    }

    void EraseRight() {
        NormalizeCaret();
        if (caret < Length()) {
            buffer.erase(caret, 1);
        }
    }

    void MoveLeft() {
        if (caret > 0) {
            caret -= 1;
        }
    }

    void MoveRight() {
        if (caret < Length()) {
            caret += 1;
        }
    }

    void MoveHome() {
        caret = 0;
    }

    void MoveEnd() {
        caret = buffer.size();
    }
};

TextEdit Current;
HPEN CaretPen;

void WindowPaint(HWND hwnd) {
    RECT clientrect;
    GetClientRect(hwnd, &clientrect);
    SIZE wndsize = {clientrect.right - clientrect.left, clientrect.bottom - clientrect.top};

    PAINTSTRUCT ps;
    HDC wnddc = BeginPaint(hwnd, &ps);
    HBITMAP bitmap = CreateCompatibleBitmap(wnddc, wndsize.cx, wndsize.cy);
    HDC dc = CreateCompatibleDC(wnddc);
    SelectObject(dc, bitmap);

    RECT wndrect = {0, 0, wndsize.cx, wndsize.cy};
    HBRUSH brush = CreateSolidBrush(RGB(255, 255, 255));
    FillRect(dc, &wndrect, brush);

    TEXTMETRICW textmetric;
    GetTextMetricsW(dc, &textmetric);

    int currentx = textmetric.tmHeight;
    int currenty = textmetric.tmHeight;
    SIZE textsize;

    TextOutW(dc, currentx, currenty, Current.Buffer(), Current.Length());

    GetTextExtentPointW(dc, Current.Buffer(), Current.caret, &textsize);
    SelectObject(dc, CaretPen);
    MoveToEx(dc, currentx + textsize.cx, currenty, nullptr);
    LineTo(dc, currentx + textsize.cx, currenty + textmetric.tmHeight);

    BitBlt(wnddc, 0, 0, wndsize.cx, wndsize.cy, dc, 0, 0, SRCCOPY);
    DeleteObject(brush);
    DeleteDC(dc);
    DeleteObject(bitmap);
    EndPaint(hwnd, &ps);
}

LRESULT CALLBACK WindowProc(
    HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam
) {
    switch (uMsg) {
    case WM_CREATE:
        CaretPen = CreatePen(PS_SOLID, 0, RGB(0, 0, 0));
        return 0;
    case WM_DESTROY:
        DeleteObject(CaretPen);
        PostQuitMessage(0);
        return 0;
    case WM_CHAR:
        wprintf(L"WM_CHAR %#4llx'%lc' %3lli\n", wParam, (wchar_t)wParam, (lParam >> 16) & 0xff);
        if (wParam == 8) {
            Current.EraseLeft();
        } else if (wParam >= 32) {
            Current.Insert(wParam);
        }
        InvalidateRect(hwnd, nullptr, false);
        return 0;
    case WM_KEYDOWN:
        wprintf(L"WM_KEYDOWN    %4lli %3lli\n", wParam, (lParam >> 16) & 0xff);
        if (wParam == VK_LEFT) {
            Current.MoveLeft();
            InvalidateRect(hwnd, nullptr, false);
        } else if (wParam == VK_RIGHT) {
            Current.MoveRight();
            InvalidateRect(hwnd, nullptr, false);
        } else if (wParam == VK_HOME || wParam == VK_PRIOR || wParam == VK_UP) {
            Current.MoveHome();
            InvalidateRect(hwnd, nullptr, false);
        } else if (wParam == VK_END || wParam == VK_NEXT || wParam == VK_DOWN) {
            Current.MoveEnd();
            InvalidateRect(hwnd, nullptr, false);
        } else if (wParam == VK_DELETE) {
            Current.EraseRight();
            InvalidateRect(hwnd, nullptr, false);
        }
        return 0;
    case WM_KEYUP:
        return 0;
    case WM_PAINT:
        WindowPaint(hwnd);
        return 0;
    default:
        return DefWindowProcW(hwnd, uMsg, wParam, lParam);
    }
}

int CALLBACK WinMain(
    HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    AllocConsole();
    freopen("CONOUT$", "w", stdout);
    const DWORD WindowStyle = WS_OVERLAPPEDWINDOW;
    WNDCLASSW wndclass;
    wndclass.style = CS_VREDRAW | CS_HREDRAW;
    wndclass.lpfnWndProc = &WindowProc;
    wndclass.cbClsExtra = 8;
    wndclass.cbWndExtra = 0;
    wndclass.hInstance = hInstance;
    wndclass.hIcon = LoadIcon(0, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(0, IDC_ARROW);
    wndclass.hbrBackground = 0;
    wndclass.lpszMenuName = 0;
    wndclass.lpszClassName = L"MyWindowClass";
    ATOM wndclassatom = RegisterClassW(&wndclass);
    RECT WindowRect = {0, 0, 800, 600};
    AdjustWindowRect(
        &WindowRect, WindowStyle, false);
    HWND hwnd = CreateWindowW(
        (LPCWSTR)wndclassatom,
        L"window",
        WindowStyle,
        20,
        20,
        WindowRect.right - WindowRect.left,
        WindowRect.bottom - WindowRect.top,
        0,
        0,
        hInstance,
        0);
    ShowWindow(hwnd, SW_SHOW);
    UpdateWindow(hwnd);
    MSG message = {0, 0, 0, 0};
    while (GetMessageW(&message, nullptr, 0, 0)) {
        TranslateMessage(&message);
        DispatchMessageW(&message);
    }
    return 0;
};