/*****************************************************************************************
 *                                                                                       *
 * OpenSpace                                                                             *
 *                                                                                       *
 * Copyright (c) 2014-2025                                                               *
 *                                                                                       *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this  *
 * software and associated documentation files (the "Software"), to deal in the Software *
 * without restriction, including without limitation the rights to use, copy, modify,    *
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to    *
 * permit persons to whom the Software is furnished to do so, subject to the following   *
 * conditions:                                                                           *
 *                                                                                       *
 * The above copyright notice and this permission notice shall be included in all copies *
 * or substantial portions of the Software.                                              *
 *                                                                                       *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,   *
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A         *
 * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT    *
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF  *
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE  *
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                                         *
 ****************************************************************************************/

#include <modules/imgui/imguimodule.h>

#include <modules/imgui/include/imgui_include.h>
#include <openspace/engine/globals.h>
#include <openspace/engine/globalscallbacks.h>
#include <openspace/engine/moduleengine.h>
#include <openspace/engine/windowdelegate.h>
#include <openspace/interaction/sessionrecordinghandler.h>
#include <openspace/navigation/navigationhandler.h>
#include <openspace/network/parallelpeer.h>
#include <openspace/rendering/dashboard.h>
#include <openspace/rendering/luaconsole.h>
#include <openspace/rendering/renderengine.h>
#include <openspace/scene/scene.h>
#include <openspace/scripting/scriptengine.h>
#include <openspace/scene/scenegraphnode.h>
#include <ghoul/filesystem/cachemanager.h>
#include <ghoul/filesystem/filesystem.h>
#include <ghoul/format.h>
#include <ghoul/logging/logmanager.h>
#include <ghoul/misc/dictionary.h>
#include <ghoul/misc/profiling.h>
#include <ghoul/opengl/programobject.h>
#include <ghoul/opengl/texture.h>
#include <ghoul/opengl/textureunit.h>
#include <ghoul/opengl/uniformcache.h>
#include <algorithm>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <filesystem>
#include <utility>

// #define SHOW_IMGUI_HELPERS

namespace {
    constexpr std::string_view _loggerCat = "GUI";
    constexpr std::string_view GuiFont = "${FONTS}/arimo/Arimo-Regular.ttf";
    constexpr float FontSize = 14.f;

    ImFont* captionFont = nullptr;

    constexpr openspace::properties::Property::PropertyInfo EnabledInfo = {
        "Enabled",
        "Enabled",
        "This setting determines whether this object will be visible or not.",
        openspace::properties::Property::Visibility::Developer
    };

    constexpr openspace::properties::Property::PropertyInfo CollapsedInfo = {
        "Collapsed",
        "Is collapsed",
        "This setting determines whether this window is collapsed or not.",
        openspace::properties::Property::Visibility::Developer
    };

    constexpr openspace::properties::Property::PropertyInfo ShowHelpInfo = {
        "ShowHelpText",
        "Show tooltip help",
        "If this value is enabled these kinds of tooltips are shown for most properties "
        "explaining what impact they have on the visuals.",
        openspace::properties::Property::Visibility::Developer
    };

    constexpr openspace::properties::Property::PropertyInfo HelpTextDelayInfo = {
        "HelpTextDelay",
        "Tooltip delay (in s)",
        "This value determines the delay in seconds after which the tooltip is shown.",
        openspace::properties::Property::Visibility::Developer
    };
} // namespace

namespace openspace {

void CaptionText(const char* text) {
    ImGui::PushFont(captionFont);
    ImGui::Text("%s", text);
    ImGui::PopFont();
}

ImGUIModule::ImGUIModule()
    : OpenSpaceModule(Name)
    , _isEnabled(EnabledInfo, false)
    , _isCollapsed(CollapsedInfo, false)
    , _sceneProperty("Scene", "Scene", gui::GuiPropertyComponent::UseTreeLayout::Yes)
    , _property("Settings", "Settings")
    , _showHelpText(ShowHelpInfo, true)
    , _helpTextDelay(HelpTextDelayInfo, 1.f, 0.f, 10.f)
{
    addProperty(_isEnabled);
    addProperty(_isCollapsed);

    for (gui::GuiComponent* comp : _components) {
        addPropertySubOwner(comp);
    }
    _spaceTime.setEnabled(true);

    {
        auto showHelpTextFunc = [this]() {
            for (gui::GuiComponent* comp : _components) {
                comp->setShowHelpTooltip(_showHelpText);
            }
        };
        showHelpTextFunc();
        _showHelpText.onChange(std::move(showHelpTextFunc));
        addProperty(_showHelpText);
    }

    {
        auto helpTextDelayFunc = [this]() {
            for (gui::GuiComponent* comp : _components) {
                comp->setShowHelpTooltipDelay(_helpTextDelay);
            }
        };
        helpTextDelayFunc();
        _helpTextDelay.onChange(std::move(helpTextDelayFunc));
        addProperty(_helpTextDelay);
    }

    global::callback::draw2D->emplace_back([this]() {
        ZoneScopedN("ImGUI");

        if (!_isEnabled || !_hasContext) {
            return;
        }

        const WindowDelegate& delegate = *global::windowDelegate;
        const bool showGui = delegate.hasGuiWindow() ? delegate.isGuiWindow() : true;
        if (delegate.isMaster() && showGui) {
            const glm::ivec2 windowSize = delegate.currentSubwindowSize();
            if (windowSize.x <= 0 || windowSize.y <= 0) {
                return;
            }

            const glm::ivec2 resolution = delegate.currentDrawBufferResolution();
            const double dt = std::max(delegate.averageDeltaTime(), 0.0);
            renderFrame(
                static_cast<float>(dt),
                glm::vec2(windowSize),
                resolution / windowSize,
                _mousePosition,
                _mouseButtons
            );
        }
    });

    global::callback::keyboard->emplace_back(
        [this](Key key, KeyModifier mod, KeyAction action,
               IsGuiWindow isGuiWindow) -> bool
        {
            ZoneScopedN("ImGUI");

            if (!isGuiWindow || !_isEnabled || !_hasContext) {
                return false;
            }
            return keyCallback(key, mod, action);
        }
    );

    global::callback::character->emplace_back(
        [this](unsigned int codepoint, KeyModifier modifier,
               IsGuiWindow isGuiWindow) -> bool
        {
            ZoneScopedN("ImGUI");

            if (!isGuiWindow || !_isEnabled || !_hasContext) {
                return false;
            }
            return charCallback(codepoint, modifier);
        }
    );

    global::callback::mousePosition->emplace_back(
        [this](double x, double y, IsGuiWindow isGuiWindow) {
            if (!isGuiWindow || !_isEnabled || !_hasContext) {
                return; // do nothing
            }
            _mousePosition = glm::vec2(static_cast<float>(x), static_cast<float>(y));
        }
    );

    global::callback::mouseButton->emplace_back(
        [this](MouseButton button, MouseAction action, KeyModifier,
               IsGuiWindow isGuiWindow) -> bool
        {
            ZoneScopedN("ImGUI");

            if (!isGuiWindow || !_isEnabled || !_hasContext) {
                return false;
            }

            if (action == MouseAction::Press) {
                _mouseButtons |= (1 << static_cast<int>(button));
            }
            else if (action == MouseAction::Release) {
                _mouseButtons &= ~(1 << static_cast<int>(button));
            }

            return _isEnabled ? mouseButtonCallback(button, action) : false;
        }
    );

    global::callback::mouseScrollWheel->emplace_back(
        [this](double, double posY, IsGuiWindow isGuiWindow) -> bool {
            ZoneScopedN("ImGUI");

            if (!isGuiWindow || !_isEnabled || !_hasContext) {
                return false;
            }
            return mouseWheelCallback(posY);
        }
    );

    global::callback::touchDetected->emplace_back(
        [this](TouchInput input) -> bool {
            if (!_isEnabled || !_hasContext) {
                return false;
            }
            return touchDetectedCallback(input);
        }
    );

    global::callback::touchUpdated->emplace_back(
        [this](TouchInput input) -> bool {
            if (!_isEnabled || !_hasContext) {
                return false;
            }
            return touchUpdatedCallback(input);
        }
    );

    global::callback::touchExit->emplace_back(
        [this](TouchInput input) {
            if (!_isEnabled || !_hasContext) {
                return;
            }
            touchExitCallback(input);
        }
    );
}

void ImGUIModule::internalInitialize(const ghoul::Dictionary&) {
    LDEBUGC("ImGUIModule", "Initializing GUI");

    _sceneProperty.setPropertyOwnerFunction(
        []() {
            const Scene* scene = global::renderEngine->scene();
            const std::vector<SceneGraphNode*>& nodes = scene ?
                scene->allSceneGraphNodes() :
                std::vector<SceneGraphNode*>();

            return std::vector<properties::PropertyOwner*>(nodes.begin(), nodes.end());
        }
    );

    _property.setPropertyOwners({
        global::screenSpaceRootPropertyOwner,
        global::moduleEngine,
        global::navigationHandler,
        global::sessionRecordingHandler,
        global::timeManager,
        global::renderEngine,
        global::parallelPeer,
        global::luaConsole,
        global::dashboard
    });
}

void ImGUIModule::internalDeinitialize() {
    for (ImGuiContext* ctx : _contexts) {
        ImGui::DestroyContext(ctx);
    }

    for (gui::GuiComponent* comp : _components) {
        comp->deinitialize();
    }

    _hasContext = false;
}

void ImGUIModule::internalInitializeGL() {
    std::filesystem::path file = FileSys.cacheManager()->cachedFilename("imgui.ini", "");
    LDEBUG(std::format("Using '{}' as ImGUI cache location", file));

    _iniFileBuffer.resize(file.string().size() + 1);

#ifdef WIN32
    strcpy_s(_iniFileBuffer.data(), file.string().size() + 1, file.string().c_str());
#else
    strcpy(_iniFileBuffer.data(), file.c_str());
#endif

    const size_t nWindows = global::windowDelegate->nWindows();
    _contexts.resize(nWindows);

    for (size_t i = 0; i < nWindows; i++) {
        _contexts[i] = ImGui::CreateContext();
        ImGui::SetCurrentContext(_contexts[i]);

        ImGuiIO& io = ImGui::GetIO();
        io.IniFilename = _iniFileBuffer.data();
        io.DeltaTime = 1.f / 60.f;
        io.KeyMap[ImGuiKey_Tab] = static_cast<int>(Key::Tab);
        io.KeyMap[ImGuiKey_LeftArrow] = static_cast<int>(Key::Left);
        io.KeyMap[ImGuiKey_RightArrow] = static_cast<int>(Key::Right);
        io.KeyMap[ImGuiKey_UpArrow] = static_cast<int>(Key::Up);
        io.KeyMap[ImGuiKey_DownArrow] = static_cast<int>(Key::Down);
        io.KeyMap[ImGuiKey_Home] = static_cast<int>(Key::Home);
        io.KeyMap[ImGuiKey_End] = static_cast<int>(Key::End);
        io.KeyMap[ImGuiKey_Delete] = static_cast<int>(Key::Delete);
        io.KeyMap[ImGuiKey_Backspace] = static_cast<int>(Key::BackSpace);
        io.KeyMap[ImGuiKey_Enter] = static_cast<int>(Key::Enter);
        io.KeyMap[ImGuiKey_Escape] = static_cast<int>(Key::Escape);
        io.KeyMap[ImGuiKey_A] = static_cast<int>(Key::A);
        io.KeyMap[ImGuiKey_C] = static_cast<int>(Key::C);
        io.KeyMap[ImGuiKey_V] = static_cast<int>(Key::V);
        io.KeyMap[ImGuiKey_X] = static_cast<int>(Key::X);
        io.KeyMap[ImGuiKey_Y] = static_cast<int>(Key::Y);
        io.KeyMap[ImGuiKey_Z] = static_cast<int>(Key::Z);

        io.Fonts->AddFontFromFileTTF(absPath(GuiFont).string().c_str(), FontSize);
        captionFont = io.Fonts->AddFontFromFileTTF(
            absPath(GuiFont).string().c_str(),
            FontSize * 1.5f
        );

        ImGuiStyle& style = ImGui::GetStyle();
        style.WindowPadding = ImVec2(4.f, 4.f);
        style.WindowRounding = 0.f;
        style.FramePadding = ImVec2(3.f, 3.f);
        style.FrameRounding = 0.f;
        style.ItemSpacing = ImVec2(3.f, 2.f);
        style.ItemInnerSpacing = ImVec2(3.f, 2.f);
        style.TouchExtraPadding = ImVec2(1.f, 1.f);
        style.IndentSpacing = 15.f;
        style.ScrollbarSize = 10.f;
        style.ScrollbarRounding = 0.f;
        style.GrabMinSize = 10.f;
        style.GrabRounding = 16.f;

        style.Colors[ImGuiCol_Text] = ImVec4(0.90f, 0.90f, 0.90f, 1.00f);
        style.Colors[ImGuiCol_TextDisabled] = ImVec4(0.60f, 0.60f, 0.60f, 1.00f);
        style.Colors[ImGuiCol_WindowBg] = ImVec4(0.13f, 0.13f, 0.13f, 0.96f);
        style.Colors[ImGuiCol_ChildBg] = ImVec4(0.00f, 0.00f, 0.00f, 0.00f);
        style.Colors[ImGuiCol_PopupBg] = ImVec4(0.05f, 0.05f, 0.10f, 0.90f);
        style.Colors[ImGuiCol_Border] = ImVec4(0.65f, 0.65f, 0.65f, 0.59f);
        style.Colors[ImGuiCol_BorderShadow] = ImVec4(0.00f, 0.00f, 0.00f, 0.00f);
        style.Colors[ImGuiCol_FrameBg] = ImVec4(0.80f, 0.80f, 0.80f, 0.30f);
        style.Colors[ImGuiCol_FrameBgHovered] = ImVec4(0.91f, 0.94f, 0.99f, 0.40f);
        style.Colors[ImGuiCol_FrameBgActive] = ImVec4(0.90f, 0.90f, 0.90f, 0.45f);
        style.Colors[ImGuiCol_TitleBg] = ImVec4(0.71f, 0.81f, 1.00f, 0.45f);
        style.Colors[ImGuiCol_TitleBgCollapsed] = ImVec4(0.71f, 0.81f, 1.00f, 0.45f);
        style.Colors[ImGuiCol_TitleBgActive] = ImVec4(0.51f, 0.69f, 1.00f, 0.63f);
        style.Colors[ImGuiCol_MenuBarBg] = ImVec4(0.26f, 0.27f, 0.33f, 0.80f);
        style.Colors[ImGuiCol_ScrollbarBg] = ImVec4(0.00f, 0.00f, 0.00f, 0.00f);
        style.Colors[ImGuiCol_ScrollbarGrab] = ImVec4(0.40f, 0.75f, 0.80f, 0.43f);
        style.Colors[ImGuiCol_ScrollbarGrabHovered] = ImVec4(0.40f, 0.75f, 0.80f, 0.65f);
        style.Colors[ImGuiCol_ScrollbarGrabActive] = ImVec4(0.40f, 0.75f, 0.80f, 0.65f);
        style.Colors[ImGuiCol_CheckMark] = ImVec4(1.00f, 1.00f, 1.00f, 0.50f);
        style.Colors[ImGuiCol_SliderGrab] = ImVec4(1.00f, 1.00f, 1.00f, 0.30f);
        style.Colors[ImGuiCol_SliderGrabActive] = ImVec4(0.50f, 0.80f, 0.76f, 1.00f);
        style.Colors[ImGuiCol_Button] = ImVec4(0.36f, 0.54f, 0.68f, 0.62f);
        style.Colors[ImGuiCol_ButtonHovered] = ImVec4(0.36f, 0.54f, 0.68f, 1.00f);
        style.Colors[ImGuiCol_ButtonActive] = ImVec4(0.36f, 0.61f, 0.81f, 1.00f);
        style.Colors[ImGuiCol_Header] = ImVec4(0.69f, 0.69f, 0.69f, 0.45f);
        style.Colors[ImGuiCol_HeaderHovered] = ImVec4(0.36f, 0.54f, 0.68f, 0.62f);
        style.Colors[ImGuiCol_HeaderActive] = ImVec4(0.53f, 0.63f, 0.87f, 0.80f);
        style.Colors[ImGuiCol_Separator] = ImVec4(0.50f, 0.50f, 0.50f, 1.00f);
        style.Colors[ImGuiCol_SeparatorHovered] = ImVec4(0.70f, 0.60f, 0.60f, 1.00f);
        style.Colors[ImGuiCol_SeparatorActive] = ImVec4(0.90f, 0.70f, 0.70f, 1.00f);
        style.Colors[ImGuiCol_ResizeGrip] = ImVec4(1.00f, 1.00f, 1.00f, 1.00f);
        style.Colors[ImGuiCol_ResizeGripHovered] = ImVec4(1.00f, 1.00f, 1.00f, 0.60f);
        style.Colors[ImGuiCol_ResizeGripActive] = ImVec4(1.00f, 1.00f, 1.00f, 0.90f);
        style.Colors[ImGuiCol_PlotLines] = ImVec4(1.00f, 1.00f, 1.00f, 1.00f);
        style.Colors[ImGuiCol_PlotLinesHovered] = ImVec4(0.90f, 0.70f, 0.00f, 1.00f);
        style.Colors[ImGuiCol_PlotHistogram] = ImVec4(0.90f, 0.70f, 0.00f, 1.00f);
        style.Colors[ImGuiCol_PlotHistogramHovered] = ImVec4(1.00f, 0.60f, 0.00f, 1.00f);
        style.Colors[ImGuiCol_TextSelectedBg] = ImVec4(0.44f, 0.63f, 1.00f, 0.35f);
        style.Colors[ImGuiCol_ModalWindowDimBg] = ImVec4(0.20f, 0.20f, 0.20f, 0.35f);
    }

    _hasContext = true;

    for (gui::GuiComponent* comp : _components) {
        comp->initialize();
    }

    _program = ghoul::opengl::ProgramObject::Build(
        "GUI",
        absPath("${MODULE_IMGUI}/shaders/gui_vs.glsl"),
        absPath("${MODULE_IMGUI}/shaders/gui_fs.glsl")
    );

    ghoul::opengl::updateUniformLocations(*_program, _uniformCache);

    {
        unsigned char* texData = nullptr;
        glm::ivec2 texSize = glm::ivec2(0, 0);
        for (size_t i = 0; i < nWindows; i++) {
            ImGui::SetCurrentContext(_contexts[i]);

            ImGui::GetIO().Fonts->GetTexDataAsRGBA32(&texData, &texSize.x, &texSize.y);
        }
        _fontTexture = std::make_unique<ghoul::opengl::Texture>(
            texData,
            glm::uvec3(texSize.x, texSize.y, 1),
            GL_TEXTURE_2D
        );
        _fontTexture->setName("Gui Text");
        _fontTexture->setDataOwnership(ghoul::opengl::Texture::TakeOwnership::No);
        _fontTexture->uploadTexture();
    }
    for (size_t i = 0; i < nWindows; i++) {
        const uintptr_t texture = static_cast<GLuint>(*_fontTexture);
        ImGui::SetCurrentContext(_contexts[i]);
        ImGui::GetIO().Fonts->TexID = reinterpret_cast<void*>(texture);
    }

    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, 0, nullptr, GL_DYNAMIC_DRAW);

    glGenBuffers(1, &vboElements);

    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    const GLuint positionAttrib = _program->attributeLocation("in_position");
    const GLuint uvAttrib = _program->attributeLocation("in_uv");
    const GLuint colorAttrib = _program->attributeLocation("in_color");

    glEnableVertexAttribArray(positionAttrib);
    glVertexAttribPointer(
        positionAttrib,
        2,
        GL_FLOAT,
        GL_FALSE,
        sizeof(ImDrawVert),
        nullptr
    );

    glEnableVertexAttribArray(uvAttrib);
    glVertexAttribPointer(
        uvAttrib,
        2,
        GL_FLOAT,
        GL_FALSE,
        sizeof(ImDrawVert),
        reinterpret_cast<GLvoid*>(offsetof(ImDrawVert, uv))
    );

    glEnableVertexAttribArray(colorAttrib);
    glVertexAttribPointer(
        colorAttrib,
        4,
        GL_UNSIGNED_BYTE,
        GL_TRUE,
        sizeof(ImDrawVert),
        reinterpret_cast<GLvoid*>(offsetof(ImDrawVert, col))
    );
    glBindVertexArray(0);

    for (gui::GuiComponent* comp : _components) {
        comp->initializeGL();
    }
}

void ImGUIModule::internalDeinitializeGL() {
    _program = nullptr;
    _fontTexture = nullptr;

    glDeleteVertexArrays(1, &vao);
    glDeleteBuffers(1, &vbo);
    glDeleteBuffers(1, &vboElements);

    for (gui::GuiComponent* comp : _components) {
        comp->deinitializeGL();
    }
}

void ImGUIModule::renderFrame(float deltaTime, const glm::vec2& windowSize,
                             const glm::vec2& dpiScaling, const glm::vec2& mousePos,
                             uint32_t mouseButtonsPressed)
{
    const int iWindow = global::windowDelegate->currentWindowId();
    ImGui::SetCurrentContext(_contexts[iWindow]);

    ImGuiIO& io = ImGui::GetIO();
    io.DisplaySize = ImVec2(windowSize.x, windowSize.y);
    io.DisplayFramebufferScale = ImVec2(dpiScaling.x, dpiScaling.y);
    io.DeltaTime = deltaTime;

    io.MousePos = ImVec2(mousePos.x, mousePos.y);

    io.MouseDown[0] = mouseButtonsPressed & (1 << 0);
    io.MouseDown[1] = mouseButtonsPressed & (1 << 1);

    ImGui::NewFrame();

    if (_program->isDirty()) {
        _program->rebuildFromFile();
        ghoul::opengl::updateUniformLocations(*_program, _uniformCache);
    }

   //
   // Render
   ImGui::SetNextWindowCollapsed(_isCollapsed);

   ImGui::Begin("OpenSpace GUI", nullptr);

   _isCollapsed = ImGui::IsWindowCollapsed();

   for (gui::GuiComponent* comp : _components) {
       bool enabled = comp->isEnabled();
       ImGui::Checkbox(comp->guiName().c_str(), &enabled);
       comp->setEnabled(enabled);
   }

#ifdef SHOW_IMGUI_HELPERS
   ImGui::Checkbox("ImGUI Internals", &_showInternals);
   if (_showInternals) {
       ImGui::Begin("Style Editor");
       ImGui::ShowStyleEditor();
       ImGui::End();

       ImGui::Begin("Test Window");
       ImGui::ShowDemoWindow();
       ImGui::End();

       ImGui::Begin("Metrics Window");
       ImGui::ShowMetricsWindow();
       ImGui::End();
   }
#endif

   ImGui::End();


    for (gui::GuiComponent* comp : _components) {
        if (comp->isEnabled()) {
            comp->render();
        }
    }

    ImGui::Render();

    // Drawing
    ImDrawData* drawData = ImGui::GetDrawData();

    // Avoid rendering when minimized, scale coordinates for retina displays
    // (screen coordinates != framebuffer coordinates)
    const GLsizei fbWidth = static_cast<GLsizei>(
        io.DisplaySize.x * io.DisplayFramebufferScale.x
    );
    const GLsizei fbHeight = static_cast<GLsizei>(
        io.DisplaySize.y * io.DisplayFramebufferScale.y
    );
    if (fbWidth == 0 || fbHeight == 0) {
        return;
    }
    drawData->ScaleClipRects(io.DisplayFramebufferScale);

    // Setup render state:
    // alpha-blending enabled, no face culling, no depth testing, scissor enabled
    glEnable(GL_BLEND);
    glBlendEquation(GL_FUNC_ADD);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glDisable(GL_CULL_FACE);
    glDisable(GL_DEPTH_TEST);
    glEnable(GL_SCISSOR_TEST);

    ghoul::opengl::TextureUnit unit;
    unit.activate();
    _fontTexture->bind();

    // Setup orthographic projection matrix
    const float width = ImGui::GetIO().DisplaySize.x;
    const float height = ImGui::GetIO().DisplaySize.y;
    glViewport(0, 0, fbWidth, fbHeight);
    const glm::mat4 ortho(
        2.f / width, 0.f, 0.f, 0.f,
        0.f, 2.f / -height, 0.f, 0.f,
        0.f, 0.f, -1.f, 0.f,
        -1.f, 1.f, 0.f, 1.f
    );
    _program->activate();

    _program->setUniform(_uniformCache.tex, unit);
    _program->setUniform(_uniformCache.ortho, ortho);

    glBindVertexArray(vao);

    for (int i = 0; i < drawData->CmdListsCount; i++) {
        const ImDrawList* cmdList = drawData->CmdLists[i];
        const ImDrawIdx* indexBufferOffset = nullptr;

        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glBufferData(
            GL_ARRAY_BUFFER,
            cmdList->VtxBuffer.size() * sizeof(ImDrawVert),
            reinterpret_cast<const GLvoid*>(&cmdList->VtxBuffer.front()),
            GL_STREAM_DRAW
        );

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboElements);
        glBufferData(
            GL_ELEMENT_ARRAY_BUFFER,
            cmdList->IdxBuffer.size() * sizeof(ImDrawIdx),
            reinterpret_cast<const GLvoid*>(&cmdList->IdxBuffer.front()),
            GL_STREAM_DRAW
        );

        for (const ImDrawCmd* pcmd = cmdList->CmdBuffer.begin();
            pcmd != cmdList->CmdBuffer.end();
            pcmd++)
        {
            if (pcmd->UserCallback) {
                pcmd->UserCallback(cmdList, pcmd);
            }
            else {
                glBindTexture(
                    GL_TEXTURE_2D,
                    static_cast<GLuint>(reinterpret_cast<intptr_t>(pcmd->TextureId))
                );
                glScissor(
                    static_cast<int>(pcmd->ClipRect.x),
                    static_cast<int>(fbHeight - pcmd->ClipRect.w),
                    static_cast<int>(pcmd->ClipRect.z - pcmd->ClipRect.x),
                    static_cast<int>(pcmd->ClipRect.w - pcmd->ClipRect.y)
                );
                glDrawElements(
                    GL_TRIANGLES,
                    static_cast<GLsizei>(pcmd->ElemCount),
                    sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT,
                    indexBufferOffset
                );
            }
            indexBufferOffset += pcmd->ElemCount;
        }
    }

    glBindVertexArray(0);
    _program->deactivate();
    glDisable(GL_SCISSOR_TEST);
}

bool ImGUIModule::mouseButtonCallback(MouseButton, MouseAction) {
    const ImGuiIO& io = ImGui::GetIO();
    const bool consumeEvent = io.WantCaptureMouse;
    return consumeEvent;
}

bool ImGUIModule::mouseWheelCallback(double position) {
    ImGuiIO& io = ImGui::GetIO();
    const bool consumeEvent = io.WantCaptureMouse;
    if (consumeEvent) {
        io.MouseWheel = static_cast<float>(position);
    }
    return consumeEvent;
}

bool ImGUIModule::keyCallback(Key key, KeyModifier modifier, KeyAction action) {
    const int keyIndex = static_cast<int>(key);
    if (keyIndex < 0) {
        return false;
    }

    const bool hasShift = hasKeyModifier(modifier, KeyModifier::Shift);
    const bool hasCtrl = hasKeyModifier(modifier, KeyModifier::Control);
    const bool hasAlt = hasKeyModifier(modifier, KeyModifier::Alt);

    ImGuiIO& io = ImGui::GetIO();

    const bool consumeEvent = io.WantCaptureKeyboard;
    if (consumeEvent) {
        if (action == KeyAction::Press) {
            io.KeysDown[keyIndex] = true;
        }
        io.KeyShift = hasShift;
        io.KeyCtrl = hasCtrl;
        io.KeyAlt = hasAlt;
    }

    // Even if the event is not consumed,
    // set keys and modifiers to false when they are released.
    if (action == KeyAction::Release) {
        io.KeysDown[keyIndex] = false;
    }
    if (!hasShift) {
        io.KeyShift = false;
    }
    if (!hasCtrl) {
        io.KeyCtrl = false;
    }
    if (!hasAlt) {
        io.KeyAlt = false;
    }

    return consumeEvent;
}

bool ImGUIModule::charCallback(unsigned int character, KeyModifier) {
    ImGuiIO& io = ImGui::GetIO();
    const bool consumeEvent = io.WantCaptureKeyboard;
    if (consumeEvent) {
        io.AddInputCharacter(static_cast<unsigned short>(character));
    }
    return consumeEvent;
}

bool ImGUIModule::touchDetectedCallback(TouchInput input) {
    ImGuiIO& io = ImGui::GetIO();
    const glm::vec2 windowPos = input.currentWindowCoordinates();
    const bool consumeEvent = io.WantCaptureMouse;

    if (!consumeEvent) {
        return false;
    }
    if (_validTouchStates.empty()) {
        io.MousePos = ImVec2(windowPos.x, windowPos.y);
        io.MouseClicked[0] = true;
    }
    _validTouchStates.push_back(input);
    return true;
}

bool ImGUIModule::touchUpdatedCallback(TouchInput input) {
    if (_validTouchStates.empty()) {
        return false;
    }
    ImGuiIO& io = ImGui::GetIO();

    auto it = std::find_if(
        _validTouchStates.cbegin(),
        _validTouchStates.cend(),
        [&input](const TouchInput& state) {
            return state.fingerId == input.fingerId &&
                   state.touchDeviceId == input.touchDeviceId;
        }
    );

    if (it == _validTouchStates.cbegin()) {
        const glm::vec2 windowPos = input.currentWindowCoordinates();
        io.MousePos = ImVec2(windowPos.x, windowPos.y);
        io.MouseClicked[0] = true;
        return true;
    }
    else if (it != _validTouchStates.cend()) {
        return true;
    }
    return false;
}

void ImGUIModule::touchExitCallback(TouchInput input) {
    if (_validTouchStates.empty()) {
        return;
    }

    const auto found = std::find_if(
        _validTouchStates.cbegin(),
        _validTouchStates.cend(),
        [&input](const TouchInput& state) {
            return state.fingerId == input.fingerId &&
                   state.touchDeviceId == input.touchDeviceId;
        }
    );

    if (found == _validTouchStates.cend()) {
        return;
    }

    ImGuiIO& io = ImGui::GetIO();
    _validTouchStates.erase(found);
    if (_validTouchStates.empty()) {
        const glm::vec2 windowPos = input.currentWindowCoordinates();
        io.MousePos = ImVec2(windowPos.x, windowPos.y);
        io.MouseClicked[0] = false;
    }
}

} // namespace openspace