按以下要求写c++代码，只需写消息处理函数：在窗口用户区中做一个简单的英文文本编辑器，基本功能： 1）能够响应键盘输入文字； 2）按Ctrl+A，实现文字底色全部变为蓝色，试着实现Ctrl+C，Ctrl+V实现复制粘贴功能，粘贴位置紧随原文之后 3）按“Ctrl+S”键能够将所输入文字存成文件 4）分别按“R”“G”“B”能够相应改变文字颜色 5）能够用键盘移动在文字键插入字母

下面是一个简单的英文文本编辑器的代码，其中实现了基本功能和部分附加功能：Ctrl+A实现选中全部文字并变蓝色，Ctrl+C和Ctrl+V实现复制和粘贴功能，Ctrl+S实现保存到文件，R、G、B分别实现文字颜色的变化，方向键实现光标的移动。

#include <windows.h>
#include <string>
#include <fstream>

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

const int ID_EDIT = 1;

bool ctrlPressed = false;
bool rPressed = false;
bool gPressed = false;
bool bPressed = false;

COLORREF textColor = RGB(0, 0, 0);
COLORREF bgColor = RGB(255, 255, 255);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    const char* CLASS_NAME = "SimpleTextEditor";
    WNDCLASS wc = {};
    wc.lpfnWndProc = WndProc;
    wc.hInstance = hInstance;
    wc.lpszClassName = CLASS_NAME;
    RegisterClass(&wc);

    HWND hWnd = CreateWindowEx(
        0,
        CLASS_NAME,
        "Simple Text Editor",
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        nullptr,
        nullptr,
        hInstance,
        nullptr
    );

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

    return 0;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) {
    static HWND hEdit;

    switch (message) {
    case WM_CREATE:
        hEdit = CreateWindowEx(
            WS_EX_CLIENTEDGE,
            "EDIT",
            "",
            WS_CHILD | WS_VISIBLE | ES_MULTILINE | ES_AUTOVSCROLL | ES_AUTOHSCROLL,
            0, 0, 0, 0,
            hWnd,
            (HMENU)ID_EDIT,
            GetModuleHandle(nullptr),
            nullptr
        );
        break;

    case WM_SIZE:
        MoveWindow(hEdit, 0, 0, LOWORD(lParam), HIWORD(lParam), TRUE);
        break;

    case WM_COMMAND:
        if (LOWORD(wParam) == ID_EDIT) {
            if (HIWORD(wParam) == EN_UPDATE) {
                // text has been updated
            }
        }
        break;

    case WM_KEYDOWN:
        if (wParam == VK_CONTROL) {
            ctrlPressed = true;
        }
        else if (ctrlPressed) {
            if (wParam == 'A') {
                SendMessage(hEdit, EM_SETSEL, 0, -1);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, RGB(0, 0, 255));
            }
            else if (wParam == 'C') {
                SendMessage(hEdit, WM_COPY, 0, 0);
            }
            else if (wParam == 'V') {
                SendMessage(hEdit, WM_PASTE, 0, 0);
            }
            else if (wParam == 'S') {
                char buffer[MAX_PATH];
                OPENFILENAME ofn = {};
                ofn.lStructSize = sizeof(ofn);
                ofn.hwndOwner = hWnd;
                ofn.lpstrFile = buffer;
                ofn.nMaxFile = MAX_PATH;
                ofn.Flags = OFN_OVERWRITEPROMPT;
                if (GetSaveFileName(&ofn)) {
                    std::ofstream file(ofn.lpstrFile);
                    int length = GetWindowTextLength(hEdit);
                    char* text = new char[length + 1];
                    GetWindowText(hEdit, text, length + 1);
                    file << text;
                    delete[] text;
                }
            }
            else if (wParam == 'R') {
                rPressed = true;
                gPressed = false;
                bPressed = false;
                textColor = RGB(255, 0, 0);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, textColor);
            }
            else if (wParam == 'G') {
                rPressed = false;
                gPressed = true;
                bPressed = false;
                textColor = RGB(0, 255, 0);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, textColor);
            }
            else if (wParam == 'B') {
                rPressed = false;
                gPressed = false;
                bPressed = true;
                textColor = RGB(0, 0, 255);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, textColor);
            }
        }
        else if (wParam == VK_LEFT) {
            int pos = SendMessage(hEdit, EM_GETSEL, 0, 0);
            SendMessage(hEdit, EM_SETSEL, pos - 1, pos - 1);
        }
        else if (wParam == VK_RIGHT) {
            int pos = SendMessage(hEdit, EM_GETSEL, 0, 0);
            SendMessage(hEdit, EM_SETSEL, pos + 1, pos + 1);
        }
        else if (wParam == VK_UP) {
            int line = SendMessage(hEdit, EM_LINEFROMCHAR, -1, 0);
            int pos = SendMessage(hEdit, EM_LINEINDEX, line - 1, 0);
            SendMessage(hEdit, EM_SETSEL, pos, pos);
        }
        else if (wParam == VK_DOWN) {
            int line = SendMessage(hEdit, EM_LINEFROMCHAR, -1, 0);
            int pos = SendMessage(hEdit, EM_LINEINDEX, line + 1, 0);
            SendMessage(hEdit, EM_SETSEL, pos, pos);
        }
        break;

    case WM_KEYUP:
        if (wParam == VK_CONTROL) {
            ctrlPressed = false;
        }
        else if (wParam == 'R') {
            if (!gPressed && !bPressed) {
                textColor = RGB(0, 0, 0);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, textColor);
            }
            rPressed = false;
        }
        else if (wParam == 'G') {
            if (!rPressed && !bPressed) {
                textColor = RGB(0, 0, 0);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, textColor);
            }
            gPressed = false;
        }
        else if (wParam == 'B') {
            if (!rPressed && !gPressed) {
                textColor = RGB(0, 0, 0);
                SendMessage(hEdit, EM_SETBKGNDCOLOR, 0, bgColor);
                SendMessage(hEdit, EM_SETTEXTCOLOR, 0, textColor);
            }
            bPressed = false;
        }
        break;

    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }

    return 0;
}