#include "app_base.h"

#include "imgui.h"
#include "imgui_impl_glfw.h"
#include "imgui_impl_opengl3.h"
#include "implot.h"
#include "implot3d.h"
#include "core/tokens.h"
#include "core/icon_font.h"
#include "core/app_settings.h"
#include "core/app_about.h"
#include "core/app_menubar.h"
#include "core/fps_overlay.h"
#include "core/logger.h"
#include "core/log_window.h"
#include "core/layout_storage.h"
#include "gfx/gl_loader.h"

#include <GLFW/glfw3.h>
#include <atomic>
#include <cstdio>
#include <cstring>
#include <filesystem>
#include <string>
#include <sys/stat.h>

#ifdef _WIN32
  #ifndef WIN32_LEAN_AND_MEAN
    #define WIN32_LEAN_AND_MEAN
  #endif
  #include <windows.h>
  #define GLFW_EXPOSE_NATIVE_WIN32
  #include <GLFW/glfw3native.h>
#else
  #include <unistd.h>
#endif

#ifdef TRACY_ENABLE
#include "tracy/Tracy.hpp"
#endif

static void glfw_error_callback(int error, const char* description) {
    fprintf(stderr, "GLFW Error %d: %s\n", error, description);
}

#ifdef _WIN32
// AltSnap (and other external window movers — tiling WMs, snap-assist) bracket
// their drag with WM_ENTERSIZEMOVE / WM_EXITSIZEMOVE messages but, unlike the
// native title-bar drag, do NOT block the application thread inside the
// modal DefWindowProc move loop. Result: the app keeps rendering and swapping
// buffers while the OS posts SetWindowPos(SWP_ASYNCWINDOWPOS) calls, racing
// the framebuffer presentation against the live window position and producing
// the visible jitter / "grab and release" flicker the user reports.
//
// Native title-bar drag has no jitter precisely because Windows enters the
// modal sizemove loop and the app stops drawing — the DWM compositor moves
// the existing buffer pixels. We replicate that contract: while sizemove is
// active, skip render + glfwSwapBuffers, only pump the message queue. As soon
// as WM_EXITSIZEMOVE arrives, normal rendering resumes.
static std::atomic<bool> g_in_sizemove{false};
static WNDPROC          g_orig_wndproc = nullptr;
static HWND             g_subclassed_hwnd = nullptr;

static LRESULT CALLBACK fn_subclass_wndproc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
    switch (msg) {
        case WM_ENTERSIZEMOVE:
            g_in_sizemove.store(true, std::memory_order_release);
            break;
        case WM_EXITSIZEMOVE:
            g_in_sizemove.store(false, std::memory_order_release);
            break;
        default: break;
    }
    return CallWindowProcW(g_orig_wndproc, hwnd, msg, wp, lp);
}

static void install_sizemove_subclass(GLFWwindow* w) {
    HWND hwnd = glfwGetWin32Window(w);
    if (!hwnd) return;
    g_subclassed_hwnd = hwnd;
    g_orig_wndproc = (WNDPROC)SetWindowLongPtrW(
        hwnd, GWLP_WNDPROC, (LONG_PTR)fn_subclass_wndproc);
}

static void uninstall_sizemove_subclass() {
    if (g_subclassed_hwnd && g_orig_wndproc) {
        SetWindowLongPtrW(g_subclassed_hwnd, GWLP_WNDPROC, (LONG_PTR)g_orig_wndproc);
    }
    g_subclassed_hwnd = nullptr;
    g_orig_wndproc = nullptr;
}

static inline bool external_sizemove_active() {
    return g_in_sizemove.load(std::memory_order_acquire);
}
#else
static inline bool external_sizemove_active() { return false; }
#endif

namespace fn {

// ============================================================================
// Local files
// ============================================================================
namespace {

std::string compute_exe_dir() {
#ifdef _WIN32
    wchar_t buf[MAX_PATH * 2];
    DWORD n = GetModuleFileNameW(nullptr, buf,
        (DWORD)(sizeof(buf) / sizeof(buf[0])));
    if (n == 0 || n >= sizeof(buf)/sizeof(buf[0])) return "";
    int u8n = WideCharToMultiByte(CP_UTF8, 0, buf, (int)n,
                                   nullptr, 0, nullptr, nullptr);
    std::string out(u8n, 0);
    WideCharToMultiByte(CP_UTF8, 0, buf, (int)n, out.data(), u8n,
                         nullptr, nullptr);
    size_t slash = out.find_last_of("/\\");
    return (slash == std::string::npos) ? "" : out.substr(0, slash);
#else
    char buf[4096];
    ssize_t n = readlink("/proc/self/exe", buf, sizeof(buf) - 1);
    if (n <= 0) return "";
    buf[n] = 0;
    std::string out(buf);
    size_t slash = out.find_last_of('/');
    return (slash == std::string::npos) ? "" : out.substr(0, slash);
#endif
}

const std::string& exe_dir_ref() {
    static std::string cached = compute_exe_dir();
    return cached;
}

const std::string& local_dir_ref() {
    static std::string cached;
    static bool inited = false;
    if (inited) return cached;
    const std::string& edir = exe_dir_ref();
    if (edir.empty()) {
        cached = "local_files";   // fallback: relativo al cwd
    } else {
        cached = edir + "/local_files";
    }
    std::error_code ec;
    std::filesystem::create_directories(cached, ec);
    inited = true;
    return cached;
}

} // namespace

const char* exe_dir() { return exe_dir_ref().c_str(); }
const char* local_dir() { return local_dir_ref().c_str(); }

const char* local_path(const char* name) {
    static thread_local std::string buf;
    buf = local_dir_ref();
    if (name && *name) {
        if (!buf.empty() && buf.back() != '/' && buf.back() != '\\') buf += '/';
        buf += name;
    }
    return buf.c_str();
}

namespace {
const std::string& asset_dir_ref() {
    static std::string cached;
    static bool inited = false;
    if (inited) return cached;
    const std::string& edir = exe_dir_ref();
    cached = edir.empty() ? std::string("assets") : edir + "/assets";
    inited = true;
    return cached;
}
} // namespace

const char* asset_dir() { return asset_dir_ref().c_str(); }

const char* asset_path(const char* name) {
    static thread_local std::string buf;
    buf = asset_dir_ref();
    if (name && *name) {
        if (!buf.empty() && buf.back() != '/' && buf.back() != '\\') buf += '/';
        buf += name;
    }
    return buf.c_str();
}

void migrate_to_local_files(const char* const* names, std::size_t n) {
    if (!names || n == 0) return;
    const std::string& ldir = local_dir_ref();
    const std::string& edir = exe_dir_ref();
    for (std::size_t i = 0; i < n; ++i) {
        const char* name = names[i];
        if (!name || !*name) continue;
        std::string dst = ldir + "/" + name;
        struct stat st{};
        if (::stat(dst.c_str(), &st) == 0) continue;   // ya existe en local

        // Buscar en exe_dir y en cwd. Mover el primero que aparezca.
        std::string cands[] = {
            edir.empty() ? std::string() : (edir + "/" + name),
            std::string(name),
        };
        for (const auto& src : cands) {
            if (src.empty() || src == dst) continue;
            if (::stat(src.c_str(), &st) != 0) continue;
            std::error_code ec;
            std::filesystem::rename(src, dst, ec);
            if (ec) {
                // Cross-device o permisos — fallback a copy + remove.
                std::filesystem::copy(src, dst,
                    std::filesystem::copy_options::recursive |
                    std::filesystem::copy_options::overwrite_existing, ec);
                if (!ec) std::filesystem::remove_all(src, ec);
            }
            std::fprintf(stdout,
                "[local_files] migrado: %s -> %s\n",
                src.c_str(), dst.c_str());
            break;
        }
    }
}

int run_app(AppConfig config, std::function<void()> render_fn) {
    // Logger primero para capturar fallos del propio init (GLFW, ventana, GL).
    if (config.log.file_path != nullptr) {
        fn_log::logger_init(
            config.log.file_path,
            static_cast<fn_log::Level>(config.log.level));
        fn_log::log_info("app start: %s", config.title ? config.title : "(no title)");
    }

    glfwSetErrorCallback(glfw_error_callback);
    if (!glfwInit()) {
        fprintf(stderr, "Failed to initialize GLFW\n");
        fn_log::log_error("GLFW init failed");
        if (config.log.file_path != nullptr) fn_log::logger_close();
        return 1;
    }

    // OpenGL 4.3 core (issue 0049b) — habilita compute shaders, SSBOs, image
    // load/store, atomic counters y debug output. Backward-compatible con
    // shaders #version 330 y con todo lo escrito para 3.3 core.
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

    GLFWwindow* window = glfwCreateWindow(config.width, config.height, config.title, nullptr, nullptr);
    if (!window) {
        fprintf(stderr, "Failed to create GLFW window\n");
        fn_log::log_error("GLFW createWindow failed (%dx%d)", config.width, config.height);
        if (config.log.file_path != nullptr) fn_log::logger_close();
        glfwTerminate();
        return 1;
    }

    glfwMakeContextCurrent(window);
    glfwSwapInterval(config.vsync ? 1 : 0);

    // Anti-jitter: when the OS moves/resizes the window externally (Windows
    // tools like AltSnap, tiling WMs, snap-assist), ImGui's viewport pos can
    // lag one frame and `UpdatePlatformWindows` reapplies the stale value via
    // glfwSetWindowPos, fighting the OS and producing visible jitter.
    // Updating the viewport struct directly from the GLFW callback closes the
    // loop in the same tick — no stale Pos can ever reach the platform sync.
    // ImGui_ImplGlfw_InitForOpenGL does NOT install pos/size callbacks, so we
    // can install ours without breaking the backend's own callback chain.
    glfwSetWindowPosCallback(window, [](GLFWwindow* w, int x, int y) {
        if (ImGui::GetCurrentContext() == nullptr) return;
        if (ImGuiViewport* vp = ImGui::FindViewportByPlatformHandle(w)) {
            vp->Pos = ImVec2((float)x, (float)y);
        }
    });
    glfwSetWindowSizeCallback(window, [](GLFWwindow* w, int cx, int cy) {
        if (ImGui::GetCurrentContext() == nullptr) return;
        if (ImGuiViewport* vp = ImGui::FindViewportByPlatformHandle(w)) {
            vp->Size = ImVec2((float)cx, (float)cy);
        }
    });

#ifdef _WIN32
    // Install Win32 WndProc subclass to detect WM_ENTERSIZEMOVE / WM_EXITSIZEMOVE.
    // External movers (AltSnap) fake these brackets without blocking the app
    // thread; we observe them and skip render+swap so the compositor moves
    // the existing buffer (same contract as native title-bar drag).
    install_sizemove_subclass(window);
#endif

    // Carga punteros a funciones GL >= 2.0 si la app lo pide. En Linux es
    // no-op; en Windows usa wglGetProcAddress (requiere ctx GL activo).
    if (config.init_gl_loader) {
        if (!fn::gfx::gl_loader_init()) {
            fprintf(stderr, "Failed to initialize GL function loader\n");
            fn_log::log_error("gl_loader_init failed");
            if (config.log.file_path != nullptr) fn_log::logger_close();
            glfwDestroyWindow(window);
            glfwTerminate();
            return 1;
        }
    }

    // Setup ImGui
    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImPlot::CreateContext();
    ImPlot3D::CreateContext();

    ImGuiIO& io = ImGui::GetIO();
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
    io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;

    // Convencion local_files: imgui.ini y app_settings.ini viven en
    // <exe_dir>/local_files/. Migra automaticamente desde el cwd o
    // exe_dir si vienen de una version previa.
    {
        static const char* legacy_names[] = {"imgui.ini", "app_settings.ini"};
        migrate_to_local_files(legacy_names,
            sizeof(legacy_names) / sizeof(legacy_names[0]));
    }
    static std::string s_imgui_ini = local_path("imgui.ini");
    io.IniFilename = s_imgui_ini.c_str();

    // Lee app_settings.ini (font_id, font_size_px, show_fps) antes de cargar
    // fuentes. Si no existe el .ini, los defaults se aplican.
    fn_ui::settings_load();

    // Auto-wiring del menu Layouts: si la app no proporciono layouts_cb y no
    // ha desactivado auto_layouts, abrimos un LayoutStorage por defecto con
    // SQLite en `<local_dir>/<auto_layouts_db>` y generamos los callbacks
    // estandar (list/save/apply/delete/reset). Asi toda app C++ obtiene el
    // menu Layouts gratis sin codigo.
    fn_ui::LayoutStorage* auto_layouts_storage = nullptr;
    fn_ui::LayoutCallbacks auto_layouts_cb;
    if (config.layouts_cb == nullptr && config.auto_layouts) {
        const char* db_name = (config.auto_layouts_db && *config.auto_layouts_db)
            ? config.auto_layouts_db : "layouts.db";
        auto_layouts_storage = fn_ui::layout_storage_open(local_path(db_name));
        if (auto_layouts_storage) {
            fn_ui::layout_storage_make_callbacks(auto_layouts_storage, auto_layouts_cb);
            config.layouts_cb = &auto_layouts_cb;

            // Restore-on-open: si hay un layout activo persistido, lo dejamos
            // pendiente para que el primer frame del main loop lo aplique via
            // layout_storage_apply_pending. Asi la app abre con el ultimo
            // layout que el usuario tenia activo. active_name se setea ya
            // optimista para reflejarlo en el menu desde el primer frame.
            std::string last = fn_ui::layout_storage_get_last_active(auto_layouts_storage);
            if (!last.empty() && fn_ui::layout_storage_apply(auto_layouts_storage, last)) {
                auto_layouts_cb.active_name = last;
                fn_log::log_info("auto_layouts: restaurado layout '%s'", last.c_str());
            }
        } else {
            fn_log::log_warn("auto_layouts: layout_storage_open fallo (%s)", db_name);
        }
    }

    // Registra info de la ventana About si la app la proveyo en AppConfig.
    if (config.about.name != nullptr) {
        fn_ui::about_window_set_info(
            config.about.name,
            config.about.version    ? config.about.version    : "",
            config.about.description ? config.about.description : "");
    }

    // Texto vectorial (Karla / Roboto / DroidSans / Cousine, segun settings)
    // + iconos Tabler mergeados al mismo tamaño en el mismo ImFont.
    fn_ui::load_fonts_from_settings();

    // ImGui 1.92+ usa style.FontSizeBase como tamaño activo (escalable sin
    // rebuild de atlas). Inicializa al valor del .ini para que el primer
    // frame ya respete el setting.
    {
        ImGuiStyle& style = ImGui::GetStyle();
        style.FontSizeBase            = fn_ui::settings().font_size_px;
        style._NextFrameFontSizeBase  = style.FontSizeBase;
    }

    if (config.viewports) {
        io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable;
    }

    // Identidad visual — ver cpp/DESIGN_SYSTEM.md
    switch (config.theme) {
        case ThemeMode::FnDark:     fn_tokens::apply_dark_theme(); break;
        case ThemeMode::ImGuiDark:  ImGui::StyleColorsDark();      break;
        case ThemeMode::ImGuiLight: ImGui::StyleColorsLight();     break;
        case ThemeMode::None:                                      break;
    }

    // When viewports are enabled, tweak WindowRounding/WindowBg so
    // platform windows look consistent with the main window
    if (config.viewports) {
        ImGuiStyle& style = ImGui::GetStyle();
        style.WindowRounding = 0.0f;
        style.Colors[ImGuiCol_WindowBg].w = 1.0f;
    }

    ImGui_ImplGlfw_InitForOpenGL(window, true);
    ImGui_ImplOpenGL3_Init("#version 330");

    // Main loop
    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();

        if (glfwGetWindowAttrib(window, GLFW_ICONIFIED)) {
            glfwWaitEvents();
            continue;
        }

        // While an external mover (AltSnap on Win32, tiling WMs) is dragging
        // the window we mirror the native title-bar contract: do not render,
        // do not swap, just pump events. The DWM compositor scrolls the last
        // presented framebuffer with the window — no race between SetWindowPos
        // (async) and glfwSwapBuffers, so no jitter. WM_EXITSIZEMOVE clears
        // the flag and the main loop resumes normal rendering.
        if (external_sizemove_active()) {
            // Bound the busy loop so the message queue gets drained but we
            // don't burn CPU when AltSnap pauses between mouse moves.
            glfwWaitEventsTimeout(0.016);
            continue;
        }

        // Anti-jitter pass 2: covers secondary viewport windows that the
        // backend creates dynamically (panels dragged outside the main).
        // Sync each viewport's Pos/Size to the OS-reported state BEFORE
        // NewFrame, so ImGui logic this tick already sees the up-to-date
        // values and UpdatePlatformWindows can't stomp them with stale data.
        if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) {
            ImGuiPlatformIO& pio = ImGui::GetPlatformIO();
            for (int i = 0; i < pio.Viewports.Size; ++i) {
                ImGuiViewport* vp = pio.Viewports[i];
                if (!vp || !vp->PlatformHandle) continue;
                GLFWwindow* gw = (GLFWwindow*)vp->PlatformHandle;
                int x = 0, y = 0, cx = 0, cy = 0;
                glfwGetWindowPos(gw, &x, &y);
                glfwGetWindowSize(gw, &cx, &cy);
                vp->Pos  = ImVec2((float)x,  (float)y);
                vp->Size = ImVec2((float)cx, (float)cy);
            }
        }

        // Tamaño de fuente: aplica via style.FontSizeBase cada frame. Cambios
        // se ven al instante (ImGui 1.92+ escala el atlas dinamicamente, no
        // hace falta rebuild).
        ImGuiStyle& style = ImGui::GetStyle();
        if (style.FontSizeBase != fn_ui::settings().font_size_px) {
            style.FontSizeBase            = fn_ui::settings().font_size_px;
            style._NextFrameFontSizeBase  = style.FontSizeBase;  // FIXME-ImGui hack
        }

        // Cambio de fuente (font_id): rebuild atlas. ImGui_ImplOpenGL3
        // refresca la GPU texture via UpdateTexture en RenderDrawData.
        if (fn_ui::settings_consume_font_dirty()) {
            fn_ui::load_fonts_from_settings();
        }

        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplGlfw_NewFrame();
        ImGui::NewFrame();

        // Si auto_layouts esta gestionando el storage, aplica el layout
        // pendiente ANTES de que el render_fn cree ventanas. Si la app gestiona
        // su propio storage, debe llamar layout_storage_apply_pending ella misma
        // dentro de render_fn (patron que ya usan shaders_lab y graph_explorer).
        if (auto_layouts_storage) {
            std::string applied = fn_ui::layout_storage_apply_pending(auto_layouts_storage);
            if (!applied.empty()) auto_layouts_cb.active_name = applied;
        }

        // Menubar canonica (View / Layouts / Settings / About) — siempre se
        // renderiza para que Settings/Logs/About esten disponibles aunque la
        // app no declare panels/layouts/view_extras propios. Se dibuja ANTES
        // del render_fn para que pueda hacer DockSpaceOverViewport debajo.
        {
            // Adapter: std::function<bool()> -> ViewMenuExtrasFn(void*).
            fn_ui::ViewMenuExtrasFn extras_fn = nullptr;
            void* extras_user = nullptr;
            if ((bool)config.view_extras) {
                extras_fn = [](void* ud) -> bool {
                    auto* fn_ptr = static_cast<std::function<bool()>*>(ud);
                    return (*fn_ptr) ? (*fn_ptr)() : false;
                };
                extras_user = (void*)&config.view_extras;
            }
            fn_ui::app_menubar(config.panels, config.panel_count,
                               config.layouts_cb, extras_fn, extras_user);
        }

        render_fn();

        // Ventana de Settings (no-op si esta cerrada).
        fn_ui::settings_window_render();

        // Ventana de Logs (no-op si esta cerrada).
        fn_ui::log_window_render();

        // Ventana About (no-op si esta cerrada).
        fn_ui::about_window_render();

        // FPS overlay si esta activado en Settings.
        if (fn_ui::settings().show_fps) {
            fps_overlay();
        }

        ImGui::Render();
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
        glClearColor(config.bg_r, config.bg_g, config.bg_b, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());

        // Multi-viewport: update and render platform windows
        if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) {
            GLFWwindow* backup_ctx = glfwGetCurrentContext();
            ImGui::UpdatePlatformWindows();
            ImGui::RenderPlatformWindowsDefault();
            glfwMakeContextCurrent(backup_ctx);
        }

        glfwSwapBuffers(window);

#ifdef TRACY_ENABLE
        FrameMark;
#endif
    }

    // Persiste settings al exit (idempotente con auto-saves del menu).
    fn_ui::settings_save();

    // Cierra el archivo de log (si la app lo abrio).
    if (config.log.file_path != nullptr) {
        fn_log::log_info("app exit");
        fn_log::logger_close();
    }

    // Save-on-close: si hay un layout activo, persiste el INI actual en su
    // slot para que la proxima apertura cargue exactamente el mismo estado
    // (incluye los retoques de docking/posiciones que el usuario hizo
    // durante la sesion). Tambien reescribe last_active por si el callback
    // se salto. Hecho ANTES de cerrar el storage. Necesita ImGui context
    // vivo (SaveIniSettingsToMemory), por eso va antes de DestroyContext.
    if (auto_layouts_storage && !auto_layouts_cb.active_name.empty()) {
        fn_ui::layout_storage_save(auto_layouts_storage, auto_layouts_cb.active_name);
        fn_ui::layout_storage_set_last_active(auto_layouts_storage, auto_layouts_cb.active_name);
    }

    // Cierra el storage de layouts auto-creado, si lo hay.
    if (auto_layouts_storage) {
        fn_ui::layout_storage_close(auto_layouts_storage);
        auto_layouts_storage = nullptr;
    }

    // Cleanup
    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplGlfw_Shutdown();
    ImPlot3D::DestroyContext();
    ImPlot::DestroyContext();
    ImGui::DestroyContext();
#ifdef _WIN32
    uninstall_sizemove_subclass();
#endif
    glfwDestroyWindow(window);
    glfwTerminate();

    return 0;
}

int run_app(std::function<void()> render_fn) {
    return run_app(AppConfig{}, render_fn);
}

} // namespace fn

#ifdef IMGUI_ENABLE_TEST_ENGINE
#include "imgui_te_engine.h"
#include "imgui_te_ui.h"
#include "imgui_te_context.h"
#include "imgui_te_exporters.h"

namespace fn {

int run_app_test(AppConfig config,
                 std::function<void()> render_fn,
                 std::function<void(::ImGuiTestEngine*)> register_tests,
                 const char* filter) {
    if (!register_tests) {
        fprintf(stderr, "run_app_test: register_tests callback is null\n");
        return 1;
    }

    glfwSetErrorCallback(glfw_error_callback);
    if (!glfwInit()) { fprintf(stderr, "GLFW init failed\n"); return 1; }

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

    GLFWwindow* window = glfwCreateWindow(
        config.width, config.height,
        config.title ? config.title : "fn_test", nullptr, nullptr);
    if (!window) { glfwTerminate(); fprintf(stderr, "createWindow failed\n"); return 1; }
    glfwMakeContextCurrent(window);
    glfwSwapInterval(0);   // tests run as fast as possible — no vsync

    if (config.init_gl_loader) {
        if (!fn::gfx::gl_loader_init()) {
            glfwDestroyWindow(window); glfwTerminate();
            fprintf(stderr, "gl_loader_init failed\n"); return 1;
        }
    }

    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImPlot::CreateContext();
    ImPlot3D::CreateContext();

    ImGuiIO& io = ImGui::GetIO();
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
    io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;
    // No viewports in tests — the engine drives the main window only.
    io.IniFilename = nullptr;   // tests don't persist .ini

    fn_ui::settings_load();
    fn_ui::load_fonts_from_settings();

    switch (config.theme) {
        case ThemeMode::FnDark:     fn_tokens::apply_dark_theme(); break;
        case ThemeMode::ImGuiDark:  ImGui::StyleColorsDark();      break;
        case ThemeMode::ImGuiLight: ImGui::StyleColorsLight();     break;
        case ThemeMode::None:                                      break;
    }

    ImGui_ImplGlfw_InitForOpenGL(window, true);
    ImGui_ImplOpenGL3_Init("#version 330");

    // --- Test engine setup ---
    ImGuiTestEngine* engine = ImGuiTestEngine_CreateContext();
    ImGuiTestEngineIO& te_io = ImGuiTestEngine_GetIO(engine);
    te_io.ConfigVerboseLevel       = ImGuiTestVerboseLevel_Info;
    te_io.ConfigVerboseLevelOnError = ImGuiTestVerboseLevel_Debug;
    te_io.ConfigRunSpeed           = ImGuiTestRunSpeed_Fast;
    te_io.ConfigStopOnError        = false;
    te_io.ConfigCaptureEnabled     = false;
    te_io.ConfigSavedSettings      = false;

    register_tests(engine);

    ImGuiTestEngine_Start(engine, ImGui::GetCurrentContext());
    ImGuiTestEngine_QueueTests(engine, ImGuiTestGroup_Tests, filter,
        ImGuiTestRunFlags_RunFromCommandLine);

    // --- Loop until tests finish ---
    bool tests_queued_done = false;
    int frames_after_done = 0;
    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();

        ImGui_ImplOpenGL3_NewFrame();
        ImGui_ImplGlfw_NewFrame();
        ImGui::NewFrame();

        render_fn();

        ImGui::Render();
        int display_w, display_h;
        glfwGetFramebufferSize(window, &display_w, &display_h);
        glViewport(0, 0, display_w, display_h);
        glClearColor(config.bg_r, config.bg_g, config.bg_b, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());

        glfwSwapBuffers(window);

        if (!tests_queued_done && ImGuiTestEngine_IsTestQueueEmpty(engine)) {
            tests_queued_done = true;
        }
        if (tests_queued_done) {
            // Let the engine flush its final state for a few frames before exit.
            if (++frames_after_done > 2) break;
        }
    }

    int count_tested = 0, count_success = 0;
    ImGuiTestEngine_GetResult(engine, count_tested, count_success);
    bool all_passed = (count_tested > 0) && (count_tested == count_success);

    ImGuiTestEngine_PrintResultSummary(engine);
    ImGuiTestEngine_Stop(engine);

    ImGui_ImplOpenGL3_Shutdown();
    ImGui_ImplGlfw_Shutdown();
    ImPlot3D::DestroyContext();
    ImPlot::DestroyContext();
    ImGui::DestroyContext();

    ImGuiTestEngine_DestroyContext(engine);

    glfwDestroyWindow(window);
    glfwTerminate();

    fprintf(stdout, "\n[fn::run_app_test] %d/%d tests passed%s\n",
            count_success, count_tested, all_passed ? "" : " — FAILED");
    return all_passed ? 0 : 1;
}

} // namespace fn
#endif // IMGUI_ENABLE_TEST_ENGINE