JUCE/modules/juce_gui_basics/native/x11/juce_linux_ScopedWindowAssociation.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2022 - Raw Material Software Limited

   JUCE is an open source library subject to commercial or open-source
   licensing.

   By using JUCE, you agree to the terms of both the JUCE 7 End-User License
   Agreement and JUCE Privacy Policy.

   End User License Agreement: www.juce.com/juce-7-licence
   Privacy Policy: www.juce.com/juce-privacy-policy

   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

extern XContext windowHandleXContext;

/*  Attaches a pointer to a given window, so that it can be retrieved with XFindContext on
    the windowHandleXContext.
*/
class ScopedWindowAssociation
{
public:
    ScopedWindowAssociation() = default;

    ScopedWindowAssociation (void* associatedIn, Window windowIn)
        : associatedPointer ([&]() -> void*
          {
              if (associatedIn == nullptr)
                  return nullptr;

              // If you hit this, there's already a pointer associated with this window.
              const auto display = XWindowSystem::getInstance()->getDisplay();
              jassert (! getAssociatedPointer (display, windowIn).has_value());

              if (X11Symbols::getInstance()->xSaveContext (display,
                                                           static_cast<XID> (windowIn),
                                                           windowHandleXContext,
                                                           unalignedPointerCast<XPointer> (associatedIn)) != 0)
              {
                  jassertfalse;
                  return nullptr;
              }

              return associatedIn;
          }()),
          window (static_cast<XID> (windowIn)) {}

    ScopedWindowAssociation (const ScopedWindowAssociation&) = delete;
    ScopedWindowAssociation& operator= (const ScopedWindowAssociation&) = delete;

    ScopedWindowAssociation (ScopedWindowAssociation&& other) noexcept
        : associatedPointer (std::exchange (other.associatedPointer, nullptr)), window (other.window) {}

    ScopedWindowAssociation& operator= (ScopedWindowAssociation&& other) noexcept
    {
        ScopedWindowAssociation { std::move (other) }.swap (*this);
        return *this;
    }

    ~ScopedWindowAssociation() noexcept
    {
        if (associatedPointer == nullptr)
            return;

        const auto display = XWindowSystem::getInstance()->getDisplay();
        const auto ptr = getAssociatedPointer (display, window);

        if (! ptr.has_value())
        {
            // If you hit this, something else has cleared this association before we were able to.
            jassertfalse;
            return;
        }

        jassert (unalignedPointerCast<XPointer> (associatedPointer) == *ptr);

        if (X11Symbols::getInstance()->xDeleteContext (display, window, windowHandleXContext) != 0)
            jassertfalse;
    }

    bool isValid() const { return associatedPointer != nullptr; }

private:
    static std::optional<XPointer> getAssociatedPointer (Display* display, Window window)
    {
        XPointer ptr{};

        if (X11Symbols::getInstance()->xFindContext (display, window, windowHandleXContext, &ptr) != 0)
            return std::nullopt;

        return ptr;
    }

    void swap (ScopedWindowAssociation& other) noexcept
    {
        std::swap (other.associatedPointer, associatedPointer);
        std::swap (other.window, window);
    }

    void* associatedPointer = nullptr;
    XID window{};
};

} // namespace juce