//! Note that this file contains code very similar to [`super::wgpu_integration`].
//! When making changes to one you often also want to apply it to the other.
//!
//! This is also very complex code, and not very pretty.
//! There is a bunch of improvements we could do,
//! like removing a bunch of `unwraps`.

#![allow(clippy::undocumented_unsafe_blocks)]

use std::{cell::RefCell, num::NonZeroU32, rc::Rc, sync::Arc, time::Instant};

use egui_winit::ActionRequested;
use glutin::{
    config::GlConfig as _,
    context::NotCurrentGlContext as _,
    display::GetGlDisplay as _,
    prelude::{GlDisplay as _, PossiblyCurrentGlContext as _},
    surface::GlSurface as _,
};
use raw_window_handle::HasWindowHandle as _;
use winit::{
    event_loop::{ActiveEventLoop, EventLoop, EventLoopProxy},
    window::{Window, WindowId},
};

use ahash::{HashMap, HashSet};
use egui::{
    DeferredViewportUiCallback, ImmediateViewport, ViewportBuilder, ViewportClass, ViewportId,
    ViewportIdMap, ViewportIdPair, ViewportInfo, ViewportOutput,
};
#[cfg(feature = "accesskit")]
use egui_winit::accesskit_winit;

use crate::{
    native::epi_integration::EpiIntegration, App, AppCreator, CreationContext, NativeOptions,
    Result, Storage,
};

use super::{
    epi_integration, event_loop_context,
    winit_integration::{create_egui_context, EventResult, UserEvent, WinitApp},
};

// ----------------------------------------------------------------------------
// Types:

pub struct GlowWinitApp<'app> {
    repaint_proxy: Arc<egui::mutex::Mutex<EventLoopProxy<UserEvent>>>,
    app_name: String,
    native_options: NativeOptions,
    running: Option<GlowWinitRunning<'app>>,

    // Note that since this `AppCreator` is FnOnce we are currently unable to support
    // re-initializing the `GlowWinitRunning` state on Android if the application
    // suspends and resumes.
    app_creator: Option<AppCreator<'app>>,
}

/// State that is initialized when the application is first starts running via
/// a Resumed event. On Android this ensures that any graphics state is only
/// initialized once the application has an associated `SurfaceView`.
struct GlowWinitRunning<'app> {
    integration: EpiIntegration,
    app: Box<dyn 'app + App>,

    // These needs to be shared with the immediate viewport renderer, hence the Rc/Arc/RefCells:
    glutin: Rc<RefCell<GlutinWindowContext>>,

    // NOTE: one painter shared by all viewports.
    painter: Rc<RefCell<egui_glow::Painter>>,
}

/// This struct will contain both persistent and temporary glutin state.
///
/// Platform Quirks:
/// * Microsoft Windows: requires that we create a window before opengl context.
/// * Android: window and surface should be destroyed when we receive a suspend event. recreate on resume event.
///
/// winit guarantees that we will get a Resumed event on startup on all platforms.
/// * Before Resumed event: `gl_config`, `gl_context` can be created at any time. on windows, a window must be created to get `gl_context`.
/// * Resumed: `gl_surface` will be created here. `window` will be re-created here for android.
/// * Suspended: on android, we drop window + surface.  on other platforms, we don't get Suspended event.
///
/// The setup is divided between the `new` fn and `on_resume` fn. we can just assume that `on_resume` is a continuation of
/// `new` fn on all platforms. only on android, do we get multiple resumed events because app can be suspended.
struct GlutinWindowContext {
    egui_ctx: egui::Context,

    swap_interval: glutin::surface::SwapInterval,
    gl_config: glutin::config::Config,

    max_texture_side: Option<usize>,

    current_gl_context: Option<glutin::context::PossiblyCurrentContext>,
    not_current_gl_context: Option<glutin::context::NotCurrentContext>,

    viewports: ViewportIdMap<Viewport>,
    viewport_from_window: HashMap<WindowId, ViewportId>,
    window_from_viewport: ViewportIdMap<WindowId>,

    focused_viewport: Option<ViewportId>,
}

struct Viewport {
    ids: ViewportIdPair,
    class: ViewportClass,
    builder: ViewportBuilder,
    deferred_commands: Vec<egui::viewport::ViewportCommand>,
    info: ViewportInfo,
    actions_requested: HashSet<egui_winit::ActionRequested>,

    /// The user-callback that shows the ui.
    /// None for immediate viewports.
    viewport_ui_cb: Option<Arc<DeferredViewportUiCallback>>,

    // These three live and die together.
    // TODO(emilk): clump them together into one struct!
    gl_surface: Option<glutin::surface::Surface<glutin::surface::WindowSurface>>,
    window: Option<Arc<Window>>,
    egui_winit: Option<egui_winit::State>,
}

// ----------------------------------------------------------------------------

impl<'app> GlowWinitApp<'app> {
    pub fn new(
        event_loop: &EventLoop<UserEvent>,
        app_name: &str,
        native_options: NativeOptions,
        app_creator: AppCreator<'app>,
    ) -> Self {
        profiling::function_scope!();
        Self {
            repaint_proxy: Arc::new(egui::mutex::Mutex::new(event_loop.create_proxy())),
            app_name: app_name.to_owned(),
            native_options,
            running: None,
            app_creator: Some(app_creator),
        }
    }

    #[expect(unsafe_code)]
    fn create_glutin_windowed_context(
        egui_ctx: &egui::Context,
        event_loop: &ActiveEventLoop,
        storage: Option<&dyn Storage>,
        native_options: &mut NativeOptions,
    ) -> Result<(GlutinWindowContext, egui_glow::Painter)> {
        profiling::function_scope!();
        let window_settings = epi_integration::load_window_settings(storage);

        let winit_window_builder = epi_integration::viewport_builder(
            egui_ctx.zoom_factor(),
            event_loop,
            native_options,
            window_settings,
        )
        .with_visible(false); // Start hidden until we render the first frame to fix white flash on startup (https://github.com/emilk/egui/pull/3631)

        let mut glutin_window_context = unsafe {
            GlutinWindowContext::new(egui_ctx, winit_window_builder, native_options, event_loop)?
        };

        // Creates the window - must come before we create our glow context
        glutin_window_context.initialize_window(ViewportId::ROOT, event_loop)?;

        {
            let viewport = &glutin_window_context.viewports[&ViewportId::ROOT];
            let window = viewport.window.as_ref().unwrap(); // Can't fail - we just called `initialize_all_viewports`
            epi_integration::apply_window_settings(window, window_settings);
        }

        let gl = unsafe {
            profiling::scope!("glow::Context::from_loader_function");
            Arc::new(glow::Context::from_loader_function(|s| {
                let s = std::ffi::CString::new(s)
                    .expect("failed to construct C string from string for gl proc address");

                glutin_window_context.get_proc_address(&s)
            }))
        };

        let painter = egui_glow::Painter::new(
            gl,
            "",
            native_options.shader_version,
            native_options.dithering,
        )?;

        Ok((glutin_window_context, painter))
    }

    fn init_run_state(
        &mut self,
        event_loop: &ActiveEventLoop,
    ) -> Result<&mut GlowWinitRunning<'app>> {
        profiling::function_scope!();

        let storage = if let Some(file) = &self.native_options.persistence_path {
            epi_integration::create_storage_with_file(file)
        } else {
            epi_integration::create_storage(
                self.native_options
                    .viewport
                    .app_id
                    .as_ref()
                    .unwrap_or(&self.app_name),
            )
        };

        let egui_ctx = create_egui_context(storage.as_deref());

        let (mut glutin, painter) = Self::create_glutin_windowed_context(
            &egui_ctx,
            event_loop,
            storage.as_deref(),
            &mut self.native_options,
        )?;
        let gl = painter.gl().clone();

        let max_texture_side = painter.max_texture_side();
        glutin.max_texture_side = Some(max_texture_side);
        for viewport in glutin.viewports.values_mut() {
            if let Some(egui_winit) = viewport.egui_winit.as_mut() {
                egui_winit.set_max_texture_side(max_texture_side);
            }
        }

        let painter = Rc::new(RefCell::new(painter));

        let integration = EpiIntegration::new(
            egui_ctx,
            &glutin.window(ViewportId::ROOT),
            &self.app_name,
            &self.native_options,
            storage,
            Some(gl.clone()),
            Some(Box::new({
                let painter = painter.clone();
                move |native| painter.borrow_mut().register_native_texture(native)
            })),
            #[cfg(feature = "wgpu")]
            None,
        );

        {
            let event_loop_proxy = self.repaint_proxy.clone();
            integration
                .egui_ctx
                .set_request_repaint_callback(move |info| {
                    log::trace!("request_repaint_callback: {info:?}");
                    let when = Instant::now() + info.delay;
                    let cumulative_pass_nr = info.current_cumulative_pass_nr;
                    event_loop_proxy
                        .lock()
                        .send_event(UserEvent::RequestRepaint {
                            viewport_id: info.viewport_id,
                            when,
                            cumulative_pass_nr,
                        })
                        .ok();
                });
        }

        #[cfg(feature = "accesskit")]
        {
            let event_loop_proxy = self.repaint_proxy.lock().clone();
            let viewport = glutin.viewports.get_mut(&ViewportId::ROOT).unwrap(); // we always have a root
            if let Viewport {
                window: Some(window),
                egui_winit: Some(egui_winit),
                ..
            } = viewport
            {
                egui_winit.init_accesskit(event_loop, window, event_loop_proxy);
            }
        }

        if self
            .native_options
            .viewport
            .mouse_passthrough
            .unwrap_or(false)
        {
            if let Err(err) = glutin.window(ViewportId::ROOT).set_cursor_hittest(false) {
                log::warn!("set_cursor_hittest(false) failed: {err}");
            }
        }

        let app_creator = std::mem::take(&mut self.app_creator)
            .expect("Single-use AppCreator has unexpectedly already been taken");

        let app: Box<dyn 'app + App> = {
            // Use latest raw_window_handle for eframe compatibility
            use raw_window_handle::{HasDisplayHandle as _, HasWindowHandle as _};

            let get_proc_address = |addr: &_| glutin.get_proc_address(addr);
            let window = glutin.window(ViewportId::ROOT);
            let cc = CreationContext {
                egui_ctx: integration.egui_ctx.clone(),
                integration_info: integration.frame.info().clone(),
                storage: integration.frame.storage(),
                gl: Some(gl),
                get_proc_address: Some(&get_proc_address),
                #[cfg(feature = "wgpu")]
                wgpu_render_state: None,
                raw_display_handle: window.display_handle().map(|h| h.as_raw()),
                raw_window_handle: window.window_handle().map(|h| h.as_raw()),
            };
            profiling::scope!("app_creator");
            app_creator(&cc).map_err(crate::Error::AppCreation)?
        };

        let glutin = Rc::new(RefCell::new(glutin));

        {
            // Create weak pointers so that we don't keep
            // state alive for too long.
            let glutin = Rc::downgrade(&glutin);
            let painter = Rc::downgrade(&painter);
            let beginning = integration.beginning;

            egui::Context::set_immediate_viewport_renderer(move |egui_ctx, immediate_viewport| {
                if let (Some(glutin), Some(painter)) = (glutin.upgrade(), painter.upgrade()) {
                    render_immediate_viewport(
                        egui_ctx,
                        &glutin,
                        &painter,
                        beginning,
                        immediate_viewport,
                    );
                } else {
                    log::warn!("render_sync_callback called after window closed");
                }
            });
        }

        Ok(self.running.insert(GlowWinitRunning {
            glutin,
            painter,
            integration,
            app,
        }))
    }
}

impl WinitApp for GlowWinitApp<'_> {
    fn egui_ctx(&self) -> Option<&egui::Context> {
        self.running.as_ref().map(|r| &r.integration.egui_ctx)
    }

    fn window(&self, window_id: WindowId) -> Option<Arc<Window>> {
        let running = self.running.as_ref()?;
        let glutin = running.glutin.borrow();
        let viewport_id = *glutin.viewport_from_window.get(&window_id)?;
        if let Some(viewport) = glutin.viewports.get(&viewport_id) {
            viewport.window.clone()
        } else {
            None
        }
    }

    fn window_id_from_viewport_id(&self, id: ViewportId) -> Option<WindowId> {
        self.running
            .as_ref()
            .and_then(|r| r.glutin.borrow().window_from_viewport.get(&id).copied())
    }

    fn save(&mut self) {
        log::debug!("WinitApp::save called");
        if let Some(running) = self.running.as_mut() {
            profiling::function_scope!();

            // This is used because of the "save on suspend" logic on Android. Once the application is suspended, there is no window associated to it, which was causing panics when `.window().expect()` was used.
            let window_opt = running.glutin.borrow().window_opt(ViewportId::ROOT);

            running
                .integration
                .save(running.app.as_mut(), window_opt.as_deref());
        }
    }

    fn save_and_destroy(&mut self) {
        if let Some(mut running) = self.running.take() {
            profiling::function_scope!();

            running.integration.save(
                running.app.as_mut(),
                Some(&running.glutin.borrow().window(ViewportId::ROOT)),
            );
            running.app.on_exit(Some(running.painter.borrow().gl()));
            running.painter.borrow_mut().destroy();
        }
    }

    fn run_ui_and_paint(
        &mut self,
        event_loop: &ActiveEventLoop,
        window_id: WindowId,
    ) -> Result<EventResult> {
        if let Some(running) = &mut self.running {
            running.run_ui_and_paint(event_loop, window_id)
        } else {
            Ok(EventResult::Wait)
        }
    }

    fn resumed(&mut self, event_loop: &ActiveEventLoop) -> crate::Result<EventResult> {
        log::debug!("Event::Resumed");

        let running = if let Some(running) = &mut self.running {
            // Not the first resume event. Create all outstanding windows.
            running
                .glutin
                .borrow_mut()
                .initialize_all_windows(event_loop);
            running
        } else {
            // First resume event. Create our root window etc.
            self.init_run_state(event_loop)?
        };
        let window_id = running.glutin.borrow().window_from_viewport[&ViewportId::ROOT];
        Ok(EventResult::RepaintNow(window_id))
    }

    fn suspended(&mut self, _: &ActiveEventLoop) -> crate::Result<EventResult> {
        if let Some(running) = &mut self.running {
            running.glutin.borrow_mut().on_suspend()?;
        }
        Ok(EventResult::Save)
    }

    fn device_event(
        &mut self,
        _: &ActiveEventLoop,
        _: winit::event::DeviceId,
        event: winit::event::DeviceEvent,
    ) -> crate::Result<EventResult> {
        if let winit::event::DeviceEvent::MouseMotion { delta } = event {
            if let Some(running) = &mut self.running {
                let mut glutin = running.glutin.borrow_mut();
                if let Some(viewport) = glutin
                    .focused_viewport
                    .and_then(|viewport| glutin.viewports.get_mut(&viewport))
                {
                    if let Some(egui_winit) = viewport.egui_winit.as_mut() {
                        egui_winit.on_mouse_motion(delta);
                    }

                    if let Some(window) = viewport.window.as_ref() {
                        return Ok(EventResult::RepaintNext(window.id()));
                    }
                }
            }
        }

        Ok(EventResult::Wait)
    }

    fn window_event(
        &mut self,
        _: &ActiveEventLoop,
        window_id: WindowId,
        event: winit::event::WindowEvent,
    ) -> Result<EventResult> {
        if let Some(running) = &mut self.running {
            Ok(running.on_window_event(window_id, &event))
        } else {
            Ok(EventResult::Wait)
        }
    }

    #[cfg(feature = "accesskit")]
    fn on_accesskit_event(&mut self, event: accesskit_winit::Event) -> crate::Result<EventResult> {
        use super::winit_integration;

        if let Some(running) = &self.running {
            let mut glutin = running.glutin.borrow_mut();
            if let Some(viewport_id) = glutin.viewport_from_window.get(&event.window_id).copied() {
                if let Some(viewport) = glutin.viewports.get_mut(&viewport_id) {
                    if let Some(egui_winit) = &mut viewport.egui_winit {
                        return Ok(winit_integration::on_accesskit_window_event(
                            egui_winit,
                            event.window_id,
                            &event.window_event,
                        ));
                    }
                }
            }
        }

        Ok(EventResult::Wait)
    }
}

impl GlowWinitRunning<'_> {
    fn run_ui_and_paint(
        &mut self,
        event_loop: &ActiveEventLoop,
        window_id: WindowId,
    ) -> Result<EventResult> {
        profiling::function_scope!();

        let Some(viewport_id) = self
            .glutin
            .borrow()
            .viewport_from_window
            .get(&window_id)
            .copied()
        else {
            return Ok(EventResult::Wait);
        };

        profiling::finish_frame!();

        let mut frame_timer = crate::stopwatch::Stopwatch::new();
        frame_timer.start();

        {
            let glutin = self.glutin.borrow();
            let viewport = &glutin.viewports[&viewport_id];
            let is_immediate = viewport.viewport_ui_cb.is_none();
            if is_immediate && viewport_id != ViewportId::ROOT {
                // This will only happen if this is an immediate viewport.
                // That means that the viewport cannot be rendered by itself and needs his parent to be rendered.
                if let Some(parent_viewport) = glutin.viewports.get(&viewport.ids.parent) {
                    if let Some(window) = parent_viewport.window.as_ref() {
                        return Ok(EventResult::RepaintNext(window.id()));
                    }
                }
                return Ok(EventResult::Wait);
            }
        }

        let (raw_input, viewport_ui_cb) = {
            let mut glutin = self.glutin.borrow_mut();
            let egui_ctx = glutin.egui_ctx.clone();
            let Some(viewport) = glutin.viewports.get_mut(&viewport_id) else {
                return Ok(EventResult::Wait);
            };
            let Some(window) = viewport.window.as_ref() else {
                return Ok(EventResult::Wait);
            };
            egui_winit::update_viewport_info(&mut viewport.info, &egui_ctx, window, false);

            let Some(egui_winit) = viewport.egui_winit.as_mut() else {
                return Ok(EventResult::Wait);
            };
            let mut raw_input = egui_winit.take_egui_input(window);
            let viewport_ui_cb = viewport.viewport_ui_cb.clone();

            self.integration.pre_update();

            raw_input.time = Some(self.integration.beginning.elapsed().as_secs_f64());
            raw_input.viewports = glutin
                .viewports
                .iter()
                .map(|(id, viewport)| (*id, viewport.info.clone()))
                .collect();

            (raw_input, viewport_ui_cb)
        };

        let clear_color = self
            .app
            .clear_color(&self.integration.egui_ctx.style().visuals);

        let has_many_viewports = self.glutin.borrow().viewports.len() > 1;
        let clear_before_update = !has_many_viewports; // HACK: for some reason, an early clear doesn't "take" on Mac with multiple viewports.

        if clear_before_update {
            // clear before we call update, so users can paint between clear-color and egui windows:

            let mut glutin = self.glutin.borrow_mut();
            let GlutinWindowContext {
                viewports,
                current_gl_context,
                not_current_gl_context,
                ..
            } = &mut *glutin;
            let viewport = &viewports[&viewport_id];
            let Some(window) = viewport.window.as_ref() else {
                return Ok(EventResult::Wait);
            };
            let Some(gl_surface) = viewport.gl_surface.as_ref() else {
                return Ok(EventResult::Wait);
            };

            let screen_size_in_pixels: [u32; 2] = window.inner_size().into();

            {
                frame_timer.pause();
                change_gl_context(current_gl_context, not_current_gl_context, gl_surface);
                frame_timer.resume();
            }

            self.painter
                .borrow()
                .clear(screen_size_in_pixels, clear_color);
        }

        // ------------------------------------------------------------
        // The update function, which could call immediate viewports,
        // so make sure we don't hold any locks here required by the immediate viewports rendeer.

        let full_output =
            self.integration
                .update(self.app.as_mut(), viewport_ui_cb.as_deref(), raw_input);

        // ------------------------------------------------------------

        let Self {
            integration,
            app,
            glutin,
            painter,
            ..
        } = self;

        let mut glutin = glutin.borrow_mut();
        let mut painter = painter.borrow_mut();

        let egui::FullOutput {
            platform_output,
            textures_delta,
            shapes,
            pixels_per_point,
            viewport_output,
        } = full_output;

        glutin.remove_viewports_not_in(&viewport_output);

        let GlutinWindowContext {
            viewports,
            current_gl_context,
            not_current_gl_context,
            ..
        } = &mut *glutin;

        let Some(viewport) = viewports.get_mut(&viewport_id) else {
            return Ok(EventResult::Wait);
        };

        viewport.info.events.clear(); // they should have been processed
        let window = viewport.window.clone().unwrap();
        let gl_surface = viewport.gl_surface.as_ref().unwrap();
        let egui_winit = viewport.egui_winit.as_mut().unwrap();

        egui_winit.handle_platform_output(&window, platform_output);

        let clipped_primitives = integration.egui_ctx.tessellate(shapes, pixels_per_point);

        {
            // We may need to switch contexts again, because of immediate viewports:
            frame_timer.pause();
            change_gl_context(current_gl_context, not_current_gl_context, gl_surface);
            frame_timer.resume();
        }

        let screen_size_in_pixels: [u32; 2] = window.inner_size().into();

        if !clear_before_update {
            painter.clear(screen_size_in_pixels, clear_color);
        }

        painter.paint_and_update_textures(
            screen_size_in_pixels,
            pixels_per_point,
            &clipped_primitives,
            &textures_delta,
        );

        {
            for action in viewport.actions_requested.drain() {
                match action {
                    ActionRequested::Screenshot(user_data) => {
                        let screenshot = painter.read_screen_rgba(screen_size_in_pixels);
                        egui_winit
                            .egui_input_mut()
                            .events
                            .push(egui::Event::Screenshot {
                                viewport_id,
                                user_data,
                                image: screenshot.into(),
                            });
                    }
                    ActionRequested::Cut => {
                        egui_winit.egui_input_mut().events.push(egui::Event::Cut);
                    }
                    ActionRequested::Copy => {
                        egui_winit.egui_input_mut().events.push(egui::Event::Copy);
                    }
                    ActionRequested::Paste => {
                        if let Some(contents) = egui_winit.clipboard_text() {
                            let contents = contents.replace("\r\n", "\n");
                            if !contents.is_empty() {
                                egui_winit
                                    .egui_input_mut()
                                    .events
                                    .push(egui::Event::Paste(contents));
                            }
                        }
                    }
                }
            }

            integration.post_rendering(&window);
        }

        {
            // vsync - don't count as frame-time:
            frame_timer.pause();
            profiling::scope!("swap_buffers");
            let context = current_gl_context
                .as_ref()
                .ok_or(egui_glow::PainterError::from(
                    "failed to get current context to swap buffers".to_owned(),
                ))?;

            gl_surface.swap_buffers(context)?;
            frame_timer.resume();
        }

        // give it time to settle:
        #[cfg(feature = "__screenshot")]
        if integration.egui_ctx.cumulative_pass_nr() == 2 {
            if let Ok(path) = std::env::var("EFRAME_SCREENSHOT_TO") {
                save_screenshot_and_exit(&path, &painter, screen_size_in_pixels);
            }
        }

        glutin.handle_viewport_output(event_loop, &integration.egui_ctx, &viewport_output);

        integration.report_frame_time(frame_timer.total_time_sec()); // don't count auto-save time as part of regular frame time

        integration.maybe_autosave(app.as_mut(), Some(&window));

        if window.is_minimized() == Some(true) {
            // On Mac, a minimized Window uses up all CPU:
            // https://github.com/emilk/egui/issues/325
            profiling::scope!("minimized_sleep");
            std::thread::sleep(std::time::Duration::from_millis(10));
        }

        if integration.should_close() {
            Ok(EventResult::Exit)
        } else {
            Ok(EventResult::Wait)
        }
    }

    fn on_window_event(
        &mut self,
        window_id: WindowId,
        event: &winit::event::WindowEvent,
    ) -> EventResult {
        let mut glutin = self.glutin.borrow_mut();
        let viewport_id = glutin.viewport_from_window.get(&window_id).copied();

        // On Windows, if a window is resized by the user, it should repaint synchronously, inside the
        // event handler.
        //
        // If this is not done, the compositor will assume that the window does not want to redraw,
        // and continue ahead.
        //
        // In eframe's case, that causes the window to rapidly flicker, as it struggles to deliver
        // new frames to the compositor in time.
        //
        // The flickering is technically glutin or glow's fault, but we should be responding properly
        // to resizes anyway, as doing so avoids dropping frames.
        //
        // See: https://github.com/emilk/egui/issues/903
        let mut repaint_asap = false;

        match event {
            winit::event::WindowEvent::Focused(new_focused) => {
                glutin.focused_viewport = new_focused.then(|| viewport_id).flatten();
            }

            winit::event::WindowEvent::Resized(physical_size) => {
                // Resize with 0 width and height is used by winit to signal a minimize event on Windows.
                // See: https://github.com/rust-windowing/winit/issues/208
                // This solves an issue where the app would panic when minimizing on Windows.
                if 0 < physical_size.width && 0 < physical_size.height {
                    if let Some(viewport_id) = viewport_id {
                        repaint_asap = true;
                        glutin.resize(viewport_id, *physical_size);
                    }
                }
            }

            winit::event::WindowEvent::CloseRequested => {
                if viewport_id == Some(ViewportId::ROOT) && self.integration.should_close() {
                    log::debug!(
                        "Received WindowEvent::CloseRequested for main viewport - shutting down."
                    );
                    return EventResult::Exit;
                }

                log::debug!("Received WindowEvent::CloseRequested for viewport {viewport_id:?}");

                if let Some(viewport_id) = viewport_id {
                    if let Some(viewport) = glutin.viewports.get_mut(&viewport_id) {
                        // Tell viewport it should close:
                        viewport.info.events.push(egui::ViewportEvent::Close);

                        // We may need to repaint both us and our parent to close the window,
                        // and perhaps twice (once to notice the close-event, once again to enforce it).
                        // `request_repaint_of` does a double-repaint though:
                        self.integration.egui_ctx.request_repaint_of(viewport_id);
                        self.integration
                            .egui_ctx
                            .request_repaint_of(viewport.ids.parent);
                    }
                }
            }

            winit::event::WindowEvent::Destroyed => {
                log::debug!(
                    "Received WindowEvent::Destroyed for viewport {:?}",
                    viewport_id
                );
                if viewport_id == Some(ViewportId::ROOT) {
                    return EventResult::Exit;
                } else {
                    return EventResult::Wait;
                }
            }

            _ => {}
        }

        if self.integration.should_close() {
            return EventResult::Exit;
        }

        let mut event_response = egui_winit::EventResponse {
            consumed: false,
            repaint: false,
        };
        if let Some(viewport_id) = viewport_id {
            if let Some(viewport) = glutin.viewports.get_mut(&viewport_id) {
                if let (Some(window), Some(egui_winit)) =
                    (&viewport.window, &mut viewport.egui_winit)
                {
                    event_response = self.integration.on_window_event(window, egui_winit, event);
                }
            } else {
                log::trace!("Ignoring event: no viewport for {viewport_id:?}");
            }
        } else {
            log::trace!("Ignoring event: no viewport_id");
        }

        if event_response.repaint {
            if repaint_asap {
                EventResult::RepaintNow(window_id)
            } else {
                EventResult::RepaintNext(window_id)
            }
        } else {
            EventResult::Wait
        }
    }
}

fn change_gl_context(
    current_gl_context: &mut Option<glutin::context::PossiblyCurrentContext>,
    not_current_gl_context: &mut Option<glutin::context::NotCurrentContext>,
    gl_surface: &glutin::surface::Surface<glutin::surface::WindowSurface>,
) {
    profiling::function_scope!();

    if !cfg!(target_os = "windows") {
        // According to https://github.com/emilk/egui/issues/4289
        // we cannot do this early-out on Windows.
        // TODO(emilk): optimize context switching on Windows too.
        // See https://github.com/emilk/egui/issues/4173

        if let Some(current_gl_context) = current_gl_context {
            profiling::scope!("is_current");
            if gl_surface.is_current(current_gl_context) {
                return; // Early-out to save a lot of time.
            }
        }
    }

    let not_current = if let Some(not_current_context) = not_current_gl_context.take() {
        not_current_context
    } else {
        profiling::scope!("make_not_current");
        current_gl_context
            .take()
            .unwrap()
            .make_not_current()
            .unwrap()
    };

    profiling::scope!("make_current");
    *current_gl_context = Some(not_current.make_current(gl_surface).unwrap());
}

impl GlutinWindowContext {
    #[expect(unsafe_code)]
    unsafe fn new(
        egui_ctx: &egui::Context,
        viewport_builder: ViewportBuilder,
        native_options: &NativeOptions,
        event_loop: &ActiveEventLoop,
    ) -> Result<Self> {
        profiling::function_scope!();

        // There is a lot of complexity with opengl creation,
        // so prefer extensive logging to get all the help we can to debug issues.

        use glutin::prelude::*;
        // convert native options to glutin options
        let hardware_acceleration = match native_options.hardware_acceleration {
            crate::HardwareAcceleration::Required => Some(true),
            crate::HardwareAcceleration::Preferred => None,
            crate::HardwareAcceleration::Off => Some(false),
        };
        let swap_interval = if native_options.vsync {
            glutin::surface::SwapInterval::Wait(NonZeroU32::MIN)
        } else {
            glutin::surface::SwapInterval::DontWait
        };
        /*  opengl setup flow goes like this:
            1. we create a configuration for opengl "Display" / "Config" creation
            2. choose between special extensions like glx or egl or wgl and use them to create config/display
            3. opengl context configuration
            4. opengl context creation
        */
        // start building config for gl display
        let config_template_builder = glutin::config::ConfigTemplateBuilder::new()
            .prefer_hardware_accelerated(hardware_acceleration)
            .with_depth_size(native_options.depth_buffer)
            .with_stencil_size(native_options.stencil_buffer)
            .with_transparency(native_options.viewport.transparent.unwrap_or(false));
        // we don't know if multi sampling option is set. so, check if its more than 0.
        let config_template_builder = if native_options.multisampling > 0 {
            config_template_builder.with_multisampling(
                native_options
                    .multisampling
                    .try_into()
                    .expect("failed to fit multisamples option of native_options into u8"),
            )
        } else {
            config_template_builder
        };

        log::debug!("trying to create glutin Display with config: {config_template_builder:?}");

        // Create GL display. This may probably create a window too on most platforms. Definitely on `MS windows`. Never on Android.
        let display_builder = glutin_winit::DisplayBuilder::new()
            // we might want to expose this option to users in the future. maybe using an env var or using native_options.
            //
            // The justification for FallbackEgl over PreferEgl is at https://github.com/emilk/egui/pull/2526#issuecomment-1400229576 .
            .with_preference(glutin_winit::ApiPreference::FallbackEgl)
            .with_window_attributes(Some(egui_winit::create_winit_window_attributes(
                egui_ctx,
                event_loop,
                viewport_builder.clone(),
            )));

        let (window, gl_config) = {
            profiling::scope!("DisplayBuilder::build");

            display_builder
                .build(
                    event_loop,
                    config_template_builder.clone(),
                    |mut config_iterator| {
                        let config = config_iterator.next().expect(
                            "failed to find a matching configuration for creating glutin config",
                        );
                        log::debug!(
                            "using the first config from config picker closure. config: {config:?}"
                        );
                        config
                    },
                )
                .map_err(|e| crate::Error::NoGlutinConfigs(config_template_builder.build(), e))?
        };
        if let Some(window) = &window {
            egui_winit::apply_viewport_builder_to_window(egui_ctx, window, &viewport_builder);
        }

        let gl_display = gl_config.display();
        log::debug!(
            "successfully created GL Display with version: {} and supported features: {:?}",
            gl_display.version_string(),
            gl_display.supported_features()
        );
        let glutin_raw_window_handle = window.as_ref().map(|w| {
            w.window_handle()
                .expect("Failed to get window handle")
                .as_raw()
        });
        log::debug!("creating gl context using raw window handle: {glutin_raw_window_handle:?}");

        // create gl context. if core context cannot be created, try gl es context as fallback.
        let context_attributes =
            glutin::context::ContextAttributesBuilder::new().build(glutin_raw_window_handle);
        let fallback_context_attributes = glutin::context::ContextAttributesBuilder::new()
            .with_context_api(glutin::context::ContextApi::Gles(None))
            .build(glutin_raw_window_handle);

        let gl_context_result = unsafe {
            profiling::scope!("create_context");
            gl_config
                .display()
                .create_context(&gl_config, &context_attributes)
        };

        let gl_context = match gl_context_result {
            Ok(it) => it,
            Err(err) => {
                log::warn!("Failed to create context using default context attributes {context_attributes:?} due to error: {err}");
                log::debug!(
                    "Retrying with fallback context attributes: {fallback_context_attributes:?}"
                );
                unsafe {
                    gl_config
                        .display()
                        .create_context(&gl_config, &fallback_context_attributes)?
                }
            }
        };
        let not_current_gl_context = Some(gl_context);

        let mut viewport_from_window = HashMap::default();
        let mut window_from_viewport = ViewportIdMap::default();
        let mut info = ViewportInfo::default();
        if let Some(window) = &window {
            viewport_from_window.insert(window.id(), ViewportId::ROOT);
            window_from_viewport.insert(ViewportId::ROOT, window.id());
            egui_winit::update_viewport_info(&mut info, egui_ctx, window, true);
        }

        let mut viewports = ViewportIdMap::default();
        viewports.insert(
            ViewportId::ROOT,
            Viewport {
                ids: ViewportIdPair::ROOT,
                class: ViewportClass::Root,
                builder: viewport_builder,
                deferred_commands: vec![],
                info,
                actions_requested: Default::default(),
                viewport_ui_cb: None,
                gl_surface: None,
                window: window.map(Arc::new),
                egui_winit: None,
            },
        );

        // the fun part with opengl gl is that we never know whether there is an error. the context creation might have failed, but
        // it could keep working until we try to make surface current or swap buffers or something else. future glutin improvements might
        // help us start from scratch again if we fail context creation and go back to preferEgl or try with different config etc..
        // https://github.com/emilk/egui/pull/2541#issuecomment-1370767582

        let mut slf = Self {
            egui_ctx: egui_ctx.clone(),
            swap_interval,
            gl_config,
            current_gl_context: None,
            not_current_gl_context,
            viewports,
            viewport_from_window,
            max_texture_side: None,
            window_from_viewport,
            focused_viewport: Some(ViewportId::ROOT),
        };

        slf.initialize_window(ViewportId::ROOT, event_loop)?;

        Ok(slf)
    }

    /// Create a surface, window, and winit integration for all viewports lacking any of that.
    ///
    /// Errors will be logged.
    fn initialize_all_windows(&mut self, event_loop: &ActiveEventLoop) {
        profiling::function_scope!();

        let viewports: Vec<ViewportId> = self.viewports.keys().copied().collect();

        for viewport_id in viewports {
            if let Err(err) = self.initialize_window(viewport_id, event_loop) {
                log::error!("Failed to initialize a window for viewport {viewport_id:?}: {err}");
            }
        }
    }

    /// Create a surface, window, and winit integration for the viewport, if missing.
    #[expect(unsafe_code)]
    pub(crate) fn initialize_window(
        &mut self,
        viewport_id: ViewportId,
        event_loop: &ActiveEventLoop,
    ) -> Result {
        profiling::function_scope!();

        let viewport = self
            .viewports
            .get_mut(&viewport_id)
            .expect("viewport doesn't exist");

        let window = if let Some(window) = &mut viewport.window {
            window
        } else {
            log::debug!("Creating a window for viewport {viewport_id:?}");
            let window_attributes = egui_winit::create_winit_window_attributes(
                &self.egui_ctx,
                event_loop,
                viewport.builder.clone(),
            );
            if window_attributes.transparent()
                && self.gl_config.supports_transparency() == Some(false)
            {
                log::error!("Cannot create transparent window: the GL config does not support it");
            }
            let window =
                glutin_winit::finalize_window(event_loop, window_attributes, &self.gl_config)?;
            egui_winit::apply_viewport_builder_to_window(
                &self.egui_ctx,
                &window,
                &viewport.builder,
            );

            egui_winit::update_viewport_info(&mut viewport.info, &self.egui_ctx, &window, true);
            viewport.window.insert(Arc::new(window))
        };

        viewport.egui_winit.get_or_insert_with(|| {
            log::debug!("Initializing egui_winit for viewport {viewport_id:?}");
            egui_winit::State::new(
                self.egui_ctx.clone(),
                viewport_id,
                event_loop,
                Some(window.scale_factor() as f32),
                event_loop.system_theme(),
                self.max_texture_side,
            )
        });

        if viewport.gl_surface.is_none() {
            log::debug!("Creating a gl_surface for viewport {viewport_id:?}");

            // surface attributes
            let (width_px, height_px): (u32, u32) = window.inner_size().into();
            let width_px = NonZeroU32::new(width_px).unwrap_or(NonZeroU32::MIN);
            let height_px = NonZeroU32::new(height_px).unwrap_or(NonZeroU32::MIN);
            let surface_attributes = {
                glutin::surface::SurfaceAttributesBuilder::<glutin::surface::WindowSurface>::new()
                    .build(
                        window
                            .window_handle()
                            .expect("Failed to get display handle")
                            .as_raw(),
                        width_px,
                        height_px,
                    )
            };

            log::trace!("creating surface with attributes: {surface_attributes:?}");
            let gl_surface = unsafe {
                self.gl_config
                    .display()
                    .create_window_surface(&self.gl_config, &surface_attributes)?
            };

            log::trace!("surface created successfully: {gl_surface:?}. making context current");

            let not_current_gl_context =
                if let Some(not_current_context) = self.not_current_gl_context.take() {
                    not_current_context
                } else {
                    self.current_gl_context
                        .take()
                        .unwrap()
                        .make_not_current()
                        .unwrap()
                };
            let current_gl_context = not_current_gl_context.make_current(&gl_surface)?;

            // try setting swap interval. but its not absolutely necessary, so don't panic on failure.
            log::trace!("made context current. setting swap interval for surface");
            if let Err(err) = gl_surface.set_swap_interval(&current_gl_context, self.swap_interval)
            {
                log::warn!("Failed to set swap interval due to error: {err}");
            }

            // we will reach this point only once in most platforms except android.
            // create window/surface/make context current once and just use them forever.

            viewport.gl_surface = Some(gl_surface);

            self.current_gl_context = Some(current_gl_context);
        }

        self.viewport_from_window.insert(window.id(), viewport_id);
        self.window_from_viewport.insert(viewport_id, window.id());

        Ok(())
    }

    /// only applies for android. but we basically drop surface + window and make context not current
    fn on_suspend(&mut self) -> Result {
        log::debug!("received suspend event. dropping window and surface");
        for viewport in self.viewports.values_mut() {
            viewport.gl_surface = None;
            viewport.window = None;
        }
        if let Some(current) = self.current_gl_context.take() {
            log::debug!("context is current, so making it non-current");
            self.not_current_gl_context = Some(current.make_not_current()?);
        } else {
            log::debug!("context is already not current??? could be duplicate suspend event");
        }
        Ok(())
    }

    fn viewport(&self, viewport_id: ViewportId) -> &Viewport {
        self.viewports
            .get(&viewport_id)
            .expect("viewport doesn't exist")
    }

    fn window_opt(&self, viewport_id: ViewportId) -> Option<Arc<Window>> {
        self.viewport(viewport_id).window.clone()
    }

    fn window(&self, viewport_id: ViewportId) -> Arc<Window> {
        self.window_opt(viewport_id)
            .expect("winit window doesn't exist")
    }

    fn resize(&mut self, viewport_id: ViewportId, physical_size: winit::dpi::PhysicalSize<u32>) {
        let width_px = NonZeroU32::new(physical_size.width).unwrap_or(NonZeroU32::MIN);
        let height_px = NonZeroU32::new(physical_size.height).unwrap_or(NonZeroU32::MIN);

        if let Some(viewport) = self.viewports.get(&viewport_id) {
            if let Some(gl_surface) = &viewport.gl_surface {
                change_gl_context(
                    &mut self.current_gl_context,
                    &mut self.not_current_gl_context,
                    gl_surface,
                );
                gl_surface.resize(
                    self.current_gl_context
                        .as_ref()
                        .expect("failed to get current context to resize surface"),
                    width_px,
                    height_px,
                );
            }
        }
    }

    fn get_proc_address(&self, addr: &std::ffi::CStr) -> *const std::ffi::c_void {
        self.gl_config.display().get_proc_address(addr)
    }

    pub(crate) fn remove_viewports_not_in(
        &mut self,
        viewport_output: &ViewportIdMap<ViewportOutput>,
    ) {
        // GC old viewports
        self.viewports
            .retain(|id, _| viewport_output.contains_key(id));
        self.viewport_from_window
            .retain(|_, id| viewport_output.contains_key(id));
        self.window_from_viewport
            .retain(|id, _| viewport_output.contains_key(id));
    }

    fn handle_viewport_output(
        &mut self,
        event_loop: &ActiveEventLoop,
        egui_ctx: &egui::Context,
        viewport_output: &ViewportIdMap<ViewportOutput>,
    ) {
        profiling::function_scope!();

        for (
            viewport_id,
            ViewportOutput {
                parent,
                class,
                builder,
                viewport_ui_cb,
                mut commands,
                repaint_delay: _, // ignored - we listened to the repaint callback instead
            },
        ) in viewport_output.clone()
        {
            let ids = ViewportIdPair::from_self_and_parent(viewport_id, parent);

            let viewport = initialize_or_update_viewport(
                &mut self.viewports,
                ids,
                class,
                builder,
                viewport_ui_cb,
            );

            if let Some(window) = &viewport.window {
                let old_inner_size = window.inner_size();

                viewport.deferred_commands.append(&mut commands);

                egui_winit::process_viewport_commands(
                    egui_ctx,
                    &mut viewport.info,
                    std::mem::take(&mut viewport.deferred_commands),
                    window,
                    &mut viewport.actions_requested,
                );

                // For Wayland : https://github.com/emilk/egui/issues/4196
                if cfg!(target_os = "linux") {
                    let new_inner_size = window.inner_size();
                    if new_inner_size != old_inner_size {
                        self.resize(viewport_id, new_inner_size);
                    }
                }
            }
        }

        // Create windows for any new viewports:
        self.initialize_all_windows(event_loop);

        self.remove_viewports_not_in(viewport_output);
    }
}

fn initialize_or_update_viewport(
    viewports: &mut ViewportIdMap<Viewport>,
    ids: ViewportIdPair,
    class: ViewportClass,
    mut builder: ViewportBuilder,
    viewport_ui_cb: Option<Arc<dyn Fn(&egui::Context) + Send + Sync>>,
) -> &mut Viewport {
    profiling::function_scope!();

    if builder.icon.is_none() {
        // Inherit icon from parent
        builder.icon = viewports
            .get_mut(&ids.parent)
            .and_then(|vp| vp.builder.icon.clone());
    }

    match viewports.entry(ids.this) {
        std::collections::hash_map::Entry::Vacant(entry) => {
            // New viewport:
            log::debug!("Creating new viewport {:?} ({:?})", ids.this, builder.title);
            entry.insert(Viewport {
                ids,
                class,
                builder,
                deferred_commands: vec![],
                info: Default::default(),
                actions_requested: Default::default(),
                viewport_ui_cb,
                window: None,
                egui_winit: None,
                gl_surface: None,
            })
        }

        std::collections::hash_map::Entry::Occupied(mut entry) => {
            // Patch an existing viewport:
            let viewport = entry.get_mut();

            viewport.ids.parent = ids.parent;
            viewport.class = class;
            viewport.viewport_ui_cb = viewport_ui_cb;

            let (mut delta_commands, recreate) = viewport.builder.patch(builder);

            if recreate {
                log::debug!(
                    "Recreating window for viewport {:?} ({:?})",
                    ids.this,
                    viewport.builder.title
                );
                viewport.window = None;
                viewport.egui_winit = None;
                viewport.gl_surface = None;
            }

            viewport.deferred_commands.append(&mut delta_commands);

            entry.into_mut()
        }
    }
}

/// This is called (via a callback) by user code to render immediate viewports,
/// i.e. viewport that are directly nested inside a parent viewport.
fn render_immediate_viewport(
    egui_ctx: &egui::Context,
    glutin: &RefCell<GlutinWindowContext>,
    painter: &RefCell<egui_glow::Painter>,
    beginning: Instant,
    immediate_viewport: ImmediateViewport<'_>,
) {
    profiling::function_scope!();

    let ImmediateViewport {
        ids,
        builder,
        mut viewport_ui_cb,
    } = immediate_viewport;

    let viewport_id = ids.this;

    {
        let mut glutin = glutin.borrow_mut();

        initialize_or_update_viewport(
            &mut glutin.viewports,
            ids,
            ViewportClass::Immediate,
            builder,
            None,
        );

        let ret = event_loop_context::with_current_event_loop(|event_loop| {
            glutin.initialize_window(viewport_id, event_loop)
        });

        if let Some(Err(err)) = ret {
            log::error!(
                "Failed to initialize a window for immediate viewport {viewport_id:?}: {err}"
            );
            return;
        }
    }

    let input = {
        let mut glutin = glutin.borrow_mut();

        let Some(viewport) = glutin.viewports.get_mut(&viewport_id) else {
            return;
        };
        let (Some(egui_winit), Some(window)) = (&mut viewport.egui_winit, &viewport.window) else {
            return;
        };
        egui_winit::update_viewport_info(&mut viewport.info, egui_ctx, window, false);

        let mut raw_input = egui_winit.take_egui_input(window);
        raw_input.viewports = glutin
            .viewports
            .iter()
            .map(|(id, viewport)| (*id, viewport.info.clone()))
            .collect();
        raw_input.time = Some(beginning.elapsed().as_secs_f64());
        raw_input
    };

    // ---------------------------------------------------
    // Call the user ui-code, which could re-entrantly call this function again!
    // No locks may be hold while calling this function.

    let egui::FullOutput {
        platform_output,
        textures_delta,
        shapes,
        pixels_per_point,
        viewport_output,
    } = egui_ctx.run(input, |ctx| {
        viewport_ui_cb(ctx);
    });

    // ---------------------------------------------------

    let clipped_primitives = egui_ctx.tessellate(shapes, pixels_per_point);

    let mut glutin = glutin.borrow_mut();

    let GlutinWindowContext {
        current_gl_context,
        not_current_gl_context,
        viewports,
        ..
    } = &mut *glutin;

    let Some(viewport) = viewports.get_mut(&viewport_id) else {
        return;
    };

    viewport.info.events.clear(); // they should have been processed

    let (Some(egui_winit), Some(window), Some(gl_surface)) = (
        &mut viewport.egui_winit,
        &viewport.window,
        &viewport.gl_surface,
    ) else {
        return;
    };

    let screen_size_in_pixels: [u32; 2] = window.inner_size().into();

    change_gl_context(current_gl_context, not_current_gl_context, gl_surface);

    let current_gl_context = current_gl_context.as_ref().unwrap();

    if !gl_surface.is_current(current_gl_context) {
        log::error!(
            "egui::show_viewport_immediate: viewport {:?} ({:?}) was not created on main thread.",
            viewport.ids.this,
            viewport.builder.title
        );
    }

    egui_glow::painter::clear(
        painter.borrow().gl(),
        screen_size_in_pixels,
        [0.0, 0.0, 0.0, 0.0],
    );

    painter.borrow_mut().paint_and_update_textures(
        screen_size_in_pixels,
        pixels_per_point,
        &clipped_primitives,
        &textures_delta,
    );

    {
        profiling::scope!("swap_buffers");
        if let Err(err) = gl_surface.swap_buffers(current_gl_context) {
            log::error!("swap_buffers failed: {err}");
        }
    }

    egui_winit.handle_platform_output(window, platform_output);

    event_loop_context::with_current_event_loop(|event_loop| {
        glutin.handle_viewport_output(event_loop, egui_ctx, &viewport_output);
    });
}

#[cfg(feature = "__screenshot")]
fn save_screenshot_and_exit(
    path: &str,
    painter: &egui_glow::Painter,
    screen_size_in_pixels: [u32; 2],
) {
    assert!(
        path.ends_with(".png"),
        "Expected EFRAME_SCREENSHOT_TO to end with '.png', got {path:?}"
    );
    let screenshot = painter.read_screen_rgba(screen_size_in_pixels);
    image::save_buffer(
        path,
        screenshot.as_raw(),
        screenshot.width() as u32,
        screenshot.height() as u32,
        image::ColorType::Rgba8,
    )
    .unwrap_or_else(|err| {
        panic!("Failed to save screenshot to {path:?}: {err}");
    });
    log::info!("Screenshot saved to {path:?}.");

    #[expect(clippy::exit)]
    std::process::exit(0);
}