Alvin/src/windows/win32_windows.cpp

// Top-level window enumeration and focus via Win32 + DWM.

#include <dwmapi.h>

#include "backends.hpp"
#include "win_util.hpp"

namespace alvin::win_impl {
namespace {

std::string processName(DWORD pid) {
    HANDLE proc = OpenProcess(PROCESS_QUERY_LIMITED_INFORMATION, FALSE, pid);
    if (!proc) return {};
    wchar_t path[MAX_PATH];
    DWORD size = MAX_PATH;
    std::string name;
    if (QueryFullProcessImageNameW(proc, 0, path, &size)) {
        std::wstring_view p(path, size);
        if (auto slash = p.find_last_of(L"\\/"); slash != std::wstring_view::npos) p.remove_prefix(slash + 1);
        name = narrow(p);
    }
    CloseHandle(proc);
    return name;
}

// Windows a user would consider "open windows" (roughly what Alt+Tab shows).
bool isUserWindow(HWND hwnd) {
    if (!IsWindowVisible(hwnd) || GetWindow(hwnd, GW_OWNER) != nullptr) return false;
    if (GetWindowLongPtrW(hwnd, GWL_EXSTYLE) & WS_EX_TOOLWINDOW) return false;
    DWORD cloaked = 0;  // hidden UWP frames and windows on other virtual desktops
    if (SUCCEEDED(DwmGetWindowAttribute(hwnd, DWMWA_CLOAKED, &cloaked, sizeof cloaked)) && cloaked) return false;
    return GetWindowTextLengthW(hwnd) > 0;
}

WindowInfo describe(HWND hwnd, HWND foreground) {
    WindowInfo w;
    w.id.value = reinterpret_cast<std::uint64_t>(hwnd);
    int len = GetWindowTextLengthW(hwnd);
    std::wstring title(static_cast<std::size_t>(len) + 1, L'\0');
    GetWindowTextW(hwnd, title.data(), len + 1);
    title.resize(static_cast<std::size_t>(len));
    w.title = narrow(title);

    DWORD pid = 0;
    GetWindowThreadProcessId(hwnd, &pid);
    w.pid = pid;
    w.appId = processName(pid);

    // Extended frame bounds exclude the invisible resize borders of Windows 10+.
    RECT r{};
    if (FAILED(DwmGetWindowAttribute(hwnd, DWMWA_EXTENDED_FRAME_BOUNDS, &r, sizeof r))) GetWindowRect(hwnd, &r);
    w.bounds = {r.left, r.top, r.right - r.left, r.bottom - r.top};

    w.focused = hwnd == foreground;
    w.minimized = IsIconic(hwnd) != 0;
    w.visible = !w.minimized;

    HMONITOR mon = MonitorFromWindow(hwnd, MONITOR_DEFAULTTONULL);
    MONITORINFO mi{};
    mi.cbSize = sizeof mi;
    if (mon && GetMonitorInfoW(mon, &mi)) {
        const RECT& m = mi.rcMonitor;
        w.fullscreen = r.left <= m.left && r.top <= m.top && r.right >= m.right && r.bottom >= m.bottom;
    }
    return w;
}

class Win32Windows final : public WindowManager {
public:
    WindowBackend backend() const override { return WindowBackend::Win32; }

    Result<std::vector<WindowInfo>> list() override {
        struct Ctx {
            HWND foreground;
            std::vector<WindowInfo> out;
        } ctx{GetForegroundWindow(), {}};
        EnumWindows(
            [](HWND hwnd, LPARAM data) -> BOOL {
                auto* c = reinterpret_cast<Ctx*>(data);
                if (isUserWindow(hwnd)) c->out.push_back(describe(hwnd, c->foreground));
                return TRUE;
            },
            reinterpret_cast<LPARAM>(&ctx));
        return std::move(ctx.out);
    }

    Result<std::optional<WindowInfo>> active() override {
        HWND fg = GetForegroundWindow();
        if (!fg) return std::optional<WindowInfo>{};
        return std::optional{describe(fg, fg)};
    }

    Status focus(WindowId id) override {
        HWND hwnd = reinterpret_cast<HWND>(id.value);
        if (!IsWindow(hwnd)) return fail(ErrorCode::NotFound, "no such window");
        if (IsIconic(hwnd)) ShowWindow(hwnd, SW_RESTORE);
        if (SetForegroundWindow(hwnd)) return {};

        // The foreground lock only lets the process that received the last input
        // change focus. A synthetic Alt tap makes us that process.
        INPUT alt[2]{};
        alt[0].type = alt[1].type = INPUT_KEYBOARD;
        alt[0].ki.wVk = alt[1].ki.wVk = VK_MENU;
        alt[1].ki.dwFlags = KEYEVENTF_KEYUP;
        SendInput(2, alt, sizeof(INPUT));
        if (SetForegroundWindow(hwnd)) return {};
        return fail(ErrorCode::PermissionDenied, "Windows refused to change the foreground window");
    }
};

}  // namespace

Result<std::unique_ptr<WindowManager>> createWin32Windows() {
    ensureDpiAware();
    return std::make_unique<Win32Windows>();
}

}  // namespace alvin::win_impl