//! Note that this file contains two similar paths - one for [`glow`], one for [`wgpu`].
//! When making changes to one you often also want to apply it to the other.

use std::time::Instant;

use winit::event_loop::{
    ControlFlow, EventLoop, EventLoopBuilder, EventLoopProxy, EventLoopWindowTarget,
};

#[cfg(feature = "accesskit")]
use egui_winit::accesskit_winit;
use egui_winit::winit;

use crate::{epi, Result};

use super::epi_integration::{self, EpiIntegration};

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

#[derive(Debug)]
pub enum UserEvent {
    RequestRepaint {
        when: Instant,
        /// What the frame number was when the repaint was _requested_.
        frame_nr: u64,
    },

    #[cfg(feature = "accesskit")]
    AccessKitActionRequest(accesskit_winit::ActionRequestEvent),
}

#[cfg(feature = "accesskit")]
impl From<accesskit_winit::ActionRequestEvent> for UserEvent {
    fn from(inner: accesskit_winit::ActionRequestEvent) -> Self {
        Self::AccessKitActionRequest(inner)
    }
}

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

pub use epi::NativeOptions;

#[derive(Debug)]
enum EventResult {
    Wait,

    /// Causes a synchronous repaint inside the event handler. This should only
    /// be used in special situations if the window must be repainted while
    /// handling a specific event. This occurs on Windows when handling resizes.
    ///
    /// `RepaintNow` creates a new frame synchronously, and should therefore
    /// only be used for extremely urgent repaints.
    RepaintNow,

    /// Queues a repaint for once the event loop handles its next redraw. Exists
    /// so that multiple input events can be handled in one frame. Does not
    /// cause any delay like `RepaintNow`.
    RepaintNext,

    RepaintAt(Instant),

    Exit,
}

trait WinitApp {
    /// The current frame number, as reported by egui.
    fn frame_nr(&self) -> u64;

    fn is_focused(&self) -> bool;

    fn integration(&self) -> Option<&EpiIntegration>;

    fn window(&self) -> Option<&winit::window::Window>;

    fn save_and_destroy(&mut self);

    fn run_ui_and_paint(&mut self) -> EventResult;

    fn on_event(
        &mut self,
        event_loop: &EventLoopWindowTarget<UserEvent>,
        event: &winit::event::Event<'_, UserEvent>,
    ) -> Result<EventResult>;
}

fn create_event_loop_builder(
    native_options: &mut epi::NativeOptions,
) -> EventLoopBuilder<UserEvent> {
    let mut event_loop_builder = winit::event_loop::EventLoopBuilder::with_user_event();

    if let Some(hook) = std::mem::take(&mut native_options.event_loop_builder) {
        hook(&mut event_loop_builder);
    }

    event_loop_builder
}

/// Access a thread-local event loop.
///
/// We reuse the event-loop so we can support closing and opening an eframe window
/// multiple times. This is just a limitation of winit.
fn with_event_loop<R>(
    mut native_options: epi::NativeOptions,
    f: impl FnOnce(&mut EventLoop<UserEvent>, NativeOptions) -> R,
) -> R {
    use std::cell::RefCell;
    thread_local!(static EVENT_LOOP: RefCell<Option<EventLoop<UserEvent>>> = RefCell::new(None));

    EVENT_LOOP.with(|event_loop| {
        // Since we want to reference NativeOptions when creating the EventLoop we can't
        // do that as part of the lazy thread local storage initialization and so we instead
        // create the event loop lazily here
        let mut event_loop = event_loop.borrow_mut();
        let event_loop = event_loop
            .get_or_insert_with(|| create_event_loop_builder(&mut native_options).build());
        f(event_loop, native_options)
    })
}

fn run_and_return(
    event_loop: &mut EventLoop<UserEvent>,
    mut winit_app: impl WinitApp,
) -> Result<()> {
    use winit::platform::run_return::EventLoopExtRunReturn as _;

    log::debug!("Entering the winit event loop (run_return)…");

    let mut next_repaint_time = Instant::now();

    let mut returned_result = Ok(());

    event_loop.run_return(|event, event_loop, control_flow| {
        let event_result = match &event {
            winit::event::Event::LoopDestroyed => {
                // On Mac, Cmd-Q we get here and then `run_return` doesn't return (despite its name),
                // so we need to save state now:
                log::debug!("Received Event::LoopDestroyed - saving app state…");
                winit_app.save_and_destroy();
                *control_flow = ControlFlow::Exit;
                return;
            }

            // Platform-dependent event handlers to workaround a winit bug
            // See: https://github.com/rust-windowing/winit/issues/987
            // See: https://github.com/rust-windowing/winit/issues/1619
            winit::event::Event::RedrawEventsCleared if cfg!(windows) => {
                next_repaint_time = extremely_far_future();
                winit_app.run_ui_and_paint()
            }
            winit::event::Event::RedrawRequested(_) if !cfg!(windows) => {
                next_repaint_time = extremely_far_future();
                winit_app.run_ui_and_paint()
            }

            winit::event::Event::UserEvent(UserEvent::RequestRepaint { when, frame_nr }) => {
                if winit_app.frame_nr() == *frame_nr {
                    log::trace!("UserEvent::RequestRepaint scheduling repaint at {when:?}");
                    EventResult::RepaintAt(*when)
                } else {
                    log::trace!("Got outdated UserEvent::RequestRepaint");
                    EventResult::Wait // old request - we've already repainted
                }
            }

            winit::event::Event::NewEvents(winit::event::StartCause::ResumeTimeReached {
                ..
            }) => {
                log::trace!("Woke up to check next_repaint_time");
                EventResult::Wait
            }

            winit::event::Event::WindowEvent { window_id, .. }
                if winit_app.window().is_none()
                    || *window_id != winit_app.window().unwrap().id() =>
            {
                // This can happen if we close a window, and then reopen a new one,
                // or if we have multiple windows open.
                EventResult::Wait
            }

            event => match winit_app.on_event(event_loop, event) {
                Ok(event_result) => event_result,
                Err(err) => {
                    log::error!("Exiting because of error: {err:?} on event {event:?}");
                    returned_result = Err(err);
                    EventResult::Exit
                }
            },
        };

        match event_result {
            EventResult::Wait => {}
            EventResult::RepaintNow => {
                log::trace!("Repaint caused by winit::Event: {:?}", event);
                if cfg!(windows) {
                    // Fix flickering on Windows, see https://github.com/emilk/egui/pull/2280
                    next_repaint_time = extremely_far_future();
                    winit_app.run_ui_and_paint();
                } else {
                    // Fix for https://github.com/emilk/egui/issues/2425
                    next_repaint_time = Instant::now();
                }
            }
            EventResult::RepaintNext => {
                log::trace!("Repaint caused by winit::Event: {:?}", event);
                next_repaint_time = Instant::now();
            }
            EventResult::RepaintAt(repaint_time) => {
                next_repaint_time = next_repaint_time.min(repaint_time);
            }
            EventResult::Exit => {
                log::debug!("Asking to exit event loop…");
                winit_app.save_and_destroy();
                *control_flow = ControlFlow::Exit;
                return;
            }
        }

        *control_flow = if next_repaint_time <= Instant::now() {
            if let Some(window) = winit_app.window() {
                log::trace!("request_redraw");
                window.request_redraw();
            }
            next_repaint_time = extremely_far_future();
            ControlFlow::Poll
        } else {
            let time_until_next = next_repaint_time.saturating_duration_since(Instant::now());
            if time_until_next < std::time::Duration::from_secs(10_000) {
                log::trace!("WaitUntil {time_until_next:?}");
            }
            ControlFlow::WaitUntil(next_repaint_time)
        };
    });

    log::debug!("eframe window closed");

    drop(winit_app);

    // On Windows this clears out events so that we can later create another window.
    // See https://github.com/emilk/egui/pull/1889 for details.
    event_loop.run_return(|_, _, control_flow| {
        control_flow.set_exit();
    });

    returned_result
}

fn run_and_exit(event_loop: EventLoop<UserEvent>, mut winit_app: impl WinitApp + 'static) -> ! {
    log::debug!("Entering the winit event loop (run)…");

    let mut next_repaint_time = Instant::now();

    event_loop.run(move |event, event_loop, control_flow| {
        let event_result = match event {
            winit::event::Event::LoopDestroyed => {
                log::debug!("Received Event::LoopDestroyed");
                EventResult::Exit
            }

            // Platform-dependent event handlers to workaround a winit bug
            // See: https://github.com/rust-windowing/winit/issues/987
            // See: https://github.com/rust-windowing/winit/issues/1619
            winit::event::Event::RedrawEventsCleared if cfg!(windows) => {
                next_repaint_time = extremely_far_future();
                winit_app.run_ui_and_paint()
            }
            winit::event::Event::RedrawRequested(_) if !cfg!(windows) => {
                next_repaint_time = extremely_far_future();
                winit_app.run_ui_and_paint()
            }

            winit::event::Event::UserEvent(UserEvent::RequestRepaint { when, frame_nr }) => {
                if winit_app.frame_nr() == frame_nr {
                    EventResult::RepaintAt(when)
                } else {
                    EventResult::Wait // old request - we've already repainted
                }
            }

            winit::event::Event::NewEvents(winit::event::StartCause::ResumeTimeReached {
                ..
            }) => EventResult::Wait, // We just woke up to check next_repaint_time

            event => match winit_app.on_event(event_loop, &event) {
                Ok(event_result) => event_result,
                Err(err) => {
                    panic!("eframe encountered a fatal error: {err}");
                }
            },
        };

        match event_result {
            EventResult::Wait => {}
            EventResult::RepaintNow => {
                if cfg!(windows) {
                    // Fix flickering on Windows, see https://github.com/emilk/egui/pull/2280
                    next_repaint_time = extremely_far_future();
                    winit_app.run_ui_and_paint();
                } else {
                    // Fix for https://github.com/emilk/egui/issues/2425
                    next_repaint_time = Instant::now();
                }
            }
            EventResult::RepaintNext => {
                next_repaint_time = Instant::now();
            }
            EventResult::RepaintAt(repaint_time) => {
                next_repaint_time = next_repaint_time.min(repaint_time);
            }
            EventResult::Exit => {
                log::debug!("Quitting - saving app state…");
                winit_app.save_and_destroy();
                #[allow(clippy::exit)]
                std::process::exit(0);
            }
        }

        *control_flow = if next_repaint_time <= Instant::now() {
            if let Some(window) = winit_app.window() {
                window.request_redraw();
            }
            next_repaint_time = extremely_far_future();
            ControlFlow::Poll
        } else {
            ControlFlow::WaitUntil(next_repaint_time)
        };
    })
}

// ----------------------------------------------------------------------------
/// Run an egui app
#[cfg(feature = "glow")]
mod glow_integration {
    use std::sync::Arc;

    use egui::NumExt as _;
    use glutin::{
        display::GetGlDisplay,
        prelude::{GlDisplay, NotCurrentGlContextSurfaceAccessor, PossiblyCurrentGlContext},
        surface::GlSurface,
    };
    use raw_window_handle::HasRawWindowHandle;

    use super::*;

    // Note: that the current Glutin API design tightly couples the GL context with
    // the Window which means it's not practically possible to just destroy the
    // window and re-create a new window while continuing to use the same GL context.
    //
    // For now this means it's not possible to support Android as well as we can with
    // wgpu because we're basically forced to destroy and recreate _everything_ when
    // the application suspends and resumes.
    //
    // There is work in progress to improve the Glutin API so it has a separate Surface
    // API that would allow us to just destroy a Window/Surface when suspending, see:
    // https://github.com/rust-windowing/glutin/pull/1435
    //

    /// 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 {
        gl: Arc<glow::Context>,
        painter: egui_glow::Painter,
        integration: epi_integration::EpiIntegration,
        app: Box<dyn epi::App>,
        // Conceptually this will be split out eventually so that the rest of the state
        // can be persistent.
        gl_window: GlutinWindowContext,
    }

    /// 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 {
        builder: winit::window::WindowBuilder,
        swap_interval: glutin::surface::SwapInterval,
        gl_config: glutin::config::Config,
        current_gl_context: Option<glutin::context::PossiblyCurrentContext>,
        gl_surface: Option<glutin::surface::Surface<glutin::surface::WindowSurface>>,
        not_current_gl_context: Option<glutin::context::NotCurrentContext>,
        window: Option<winit::window::Window>,
    }

    impl GlutinWindowContext {
        /// There is a lot of complexity with opengl creation, so prefer extensive logging to get all the help we can to debug issues.
        ///
        #[allow(unsafe_code)]
        unsafe fn new(
            winit_window_builder: winit::window::WindowBuilder,
            native_options: &epi::NativeOptions,
            event_loop: &EventLoopWindowTarget<UserEvent>,
        ) -> Result<Self> {
            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(std::num::NonZeroU32::new(1).unwrap())
            } 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.transparent);
            // 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 (window, gl_config) = 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.
                .with_preference(glutin_winit::ApiPrefence::FallbackEgl) // https://github.com/emilk/egui/issues/2520#issuecomment-1367841150
                .with_window_builder(Some(winit_window_builder.clone()))
                .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))?;

            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 raw_window_handle = window.as_ref().map(|w| w.raw_window_handle());
            log::debug!(
                "creating gl context using raw window handle: {:?}",
                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(raw_window_handle);
            let fallback_context_attributes = glutin::context::ContextAttributesBuilder::new()
                .with_context_api(glutin::context::ContextApi::Gles(None))
                .build(raw_window_handle);
            let gl_context = match gl_config
                .display()
                .create_context(&gl_config, &context_attributes)
            {
                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:?}");
                    gl_config
                        .display()
                        .create_context(&gl_config, &fallback_context_attributes)?
                }
            };
            let not_current_gl_context = Some(gl_context);

            // 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
            Ok(GlutinWindowContext {
                builder: winit_window_builder,
                swap_interval,
                gl_config,
                current_gl_context: None,
                window,
                gl_surface: None,
                not_current_gl_context,
            })
        }

        /// This will be run after `new`. on android, it might be called multiple times over the course of the app's lifetime.
        /// roughly,
        /// 1. check if window already exists. otherwise, create one now.
        /// 2. create attributes for surface creation.
        /// 3. create surface.
        /// 4. make surface and context current.
        ///
        /// we presently assume that we will
        #[allow(unsafe_code)]
        fn on_resume(&mut self, event_loop: &EventLoopWindowTarget<UserEvent>) -> Result<()> {
            if self.gl_surface.is_some() {
                log::warn!("on_resume called even thought we already have a surface. early return");
                return Ok(());
            }
            log::debug!("running on_resume fn.");
            // make sure we have a window or create one.
            let window = self.window.take().unwrap_or_else(|| {
                log::debug!("window doesn't exist yet. creating one now with finalize_window");
                glutin_winit::finalize_window(event_loop, self.builder.clone(), &self.gl_config)
                    .expect("failed to finalize glutin window")
            });
            // surface attributes
            let (width, height): (u32, u32) = window.inner_size().into();
            let width = std::num::NonZeroU32::new(width.at_least(1)).unwrap();
            let height = std::num::NonZeroU32::new(height.at_least(1)).unwrap();
            let surface_attributes =
                glutin::surface::SurfaceAttributesBuilder::<glutin::surface::WindowSurface>::new()
                    .build(window.raw_window_handle(), width, height);
            log::debug!(
                "creating surface with attributes: {:?}",
                &surface_attributes
            );
            // create surface
            let gl_surface = unsafe {
                self.gl_config
                    .display()
                    .create_window_surface(&self.gl_config, &surface_attributes)?
            };
            log::debug!("surface created successfully: {gl_surface:?}.making context current");
            // make surface and context current.
            let not_current_gl_context = self
                .not_current_gl_context
                .take()
                .expect("failed to get not current context after resume event. impossible!");
            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::debug!("made context current. setting swap interval for surface");
            if let Err(e) = gl_surface.set_swap_interval(&current_gl_context, self.swap_interval) {
                log::error!("failed to set swap interval due to error: {e:?}");
            }
            // we will reach this point only once in most platforms except android.
            // create window/surface/make context current once and just use them forever.
            self.gl_surface = Some(gl_surface);
            self.current_gl_context = Some(current_gl_context);
            self.window = Some(window);
            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");
            self.gl_surface.take();
            self.window.take();
            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 window(&self) -> &winit::window::Window {
            self.window.as_ref().expect("winit window doesn't exist")
        }

        fn resize(&self, physical_size: winit::dpi::PhysicalSize<u32>) {
            let width = std::num::NonZeroU32::new(physical_size.width.at_least(1)).unwrap();
            let height = std::num::NonZeroU32::new(physical_size.height.at_least(1)).unwrap();
            self.gl_surface
                .as_ref()
                .expect("failed to get surface to resize")
                .resize(
                    self.current_gl_context
                        .as_ref()
                        .expect("failed to get current context to resize surface"),
                    width,
                    height,
                );
        }

        fn swap_buffers(&self) -> glutin::error::Result<()> {
            self.gl_surface
                .as_ref()
                .expect("failed to get surface to swap buffers")
                .swap_buffers(
                    self.current_gl_context
                        .as_ref()
                        .expect("failed to get current context to swap buffers"),
                )
        }

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

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

        // 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<epi::AppCreator>,
        is_focused: bool,
    }

    impl GlowWinitApp {
        fn new(
            event_loop: &EventLoop<UserEvent>,
            app_name: &str,
            native_options: epi::NativeOptions,
            app_creator: epi::AppCreator,
        ) -> Self {
            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),
                is_focused: true,
            }
        }

        #[allow(unsafe_code)]
        fn create_glutin_windowed_context(
            event_loop: &EventLoopWindowTarget<UserEvent>,
            storage: Option<&dyn epi::Storage>,
            title: &str,
            native_options: &NativeOptions,
        ) -> Result<(GlutinWindowContext, glow::Context)> {
            crate::profile_function!();

            let window_settings = epi_integration::load_window_settings(storage);

            let winit_window_builder =
                epi_integration::window_builder(event_loop, title, native_options, window_settings);
            let mut glutin_window_context = unsafe {
                GlutinWindowContext::new(winit_window_builder, native_options, event_loop)?
            };
            glutin_window_context.on_resume(event_loop)?;

            if let Some(window) = &glutin_window_context.window {
                epi_integration::apply_native_options_to_window(window, native_options);
            }

            let gl = unsafe {
                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)
                })
            };

            Ok((glutin_window_context, gl))
        }

        fn init_run_state(&mut self, event_loop: &EventLoopWindowTarget<UserEvent>) -> Result<()> {
            let storage = epi_integration::create_storage(&self.app_name);

            let (gl_window, gl) = Self::create_glutin_windowed_context(
                event_loop,
                storage.as_deref(),
                &self.app_name,
                &self.native_options,
            )?;
            let gl = Arc::new(gl);

            let painter =
                egui_glow::Painter::new(gl.clone(), "", self.native_options.shader_version)
                    .unwrap_or_else(|error| panic!("some OpenGL error occurred {}\n", error));

            let system_theme = system_theme(gl_window.window(), &self.native_options);
            let mut integration = epi_integration::EpiIntegration::new(
                event_loop,
                painter.max_texture_side(),
                gl_window.window(),
                system_theme,
                &self.app_name,
                &self.native_options,
                storage,
                Some(gl.clone()),
                #[cfg(feature = "wgpu")]
                None,
            );
            #[cfg(feature = "accesskit")]
            {
                integration.init_accesskit(gl_window.window(), self.repaint_proxy.lock().clone());
            }
            let theme = system_theme.unwrap_or(self.native_options.default_theme);
            integration.egui_ctx.set_visuals(theme.egui_visuals());

            gl_window.window().set_ime_allowed(true);
            if self.native_options.mouse_passthrough {
                gl_window.window().set_cursor_hittest(false).unwrap();
            }

            {
                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.after;
                        let frame_nr = info.current_frame_nr;
                        event_loop_proxy
                            .lock()
                            .send_event(UserEvent::RequestRepaint { when, frame_nr })
                            .ok();
                    });
            }

            let app_creator = std::mem::take(&mut self.app_creator)
                .expect("Single-use AppCreator has unexpectedly already been taken");
            let mut app = app_creator(&epi::CreationContext {
                egui_ctx: integration.egui_ctx.clone(),
                integration_info: integration.frame.info(),
                storage: integration.frame.storage(),
                gl: Some(gl.clone()),
                #[cfg(feature = "wgpu")]
                wgpu_render_state: None,
            });

            if app.warm_up_enabled() {
                integration.warm_up(app.as_mut(), gl_window.window());
            }

            self.running = Some(GlowWinitRunning {
                gl_window,
                gl,
                painter,
                integration,
                app,
            });

            Ok(())
        }
    }

    impl WinitApp for GlowWinitApp {
        fn frame_nr(&self) -> u64 {
            self.running
                .as_ref()
                .map_or(0, |r| r.integration.egui_ctx.frame_nr())
        }

        fn is_focused(&self) -> bool {
            self.is_focused
        }

        fn integration(&self) -> Option<&EpiIntegration> {
            self.running.as_ref().map(|r| &r.integration)
        }

        fn window(&self) -> Option<&winit::window::Window> {
            self.running.as_ref().map(|r| r.gl_window.window())
        }

        fn save_and_destroy(&mut self) {
            if let Some(mut running) = self.running.take() {
                running
                    .integration
                    .save(running.app.as_mut(), running.gl_window.window());
                running.app.on_exit(Some(&running.gl));
                running.painter.destroy();
            }
        }

        fn run_ui_and_paint(&mut self) -> EventResult {
            if let Some(running) = &mut self.running {
                #[cfg(feature = "puffin")]
                puffin::GlobalProfiler::lock().new_frame();
                crate::profile_scope!("frame");

                let GlowWinitRunning {
                    gl_window,
                    gl,
                    app,
                    integration,
                    painter,
                } = running;

                let window = gl_window.window();

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

                egui_glow::painter::clear(
                    gl,
                    screen_size_in_pixels,
                    app.clear_color(&integration.egui_ctx.style().visuals),
                );

                let egui::FullOutput {
                    platform_output,
                    repaint_after,
                    textures_delta,
                    shapes,
                } = integration.update(app.as_mut(), window);

                integration.handle_platform_output(window, platform_output);

                let clipped_primitives = {
                    crate::profile_scope!("tessellate");
                    integration.egui_ctx.tessellate(shapes)
                };

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

                let screenshot_requested = &mut integration.frame.output.screenshot_requested;

                if *screenshot_requested {
                    *screenshot_requested = false;
                    let screenshot = painter.read_screen_rgba(screen_size_in_pixels);
                    integration.frame.screenshot.set(Some(screenshot));
                }

                integration.post_rendering(app.as_mut(), window);

                {
                    crate::profile_scope!("swap_buffers");
                    gl_window.swap_buffers().unwrap();
                }

                integration.post_present(window);

                #[cfg(feature = "__screenshot")]
                // give it time to settle:
                if integration.egui_ctx.frame_nr() == 2 {
                    if let Ok(path) = std::env::var("EFRAME_SCREENSHOT_TO") {
                        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}");
                        });
                        eprintln!("Screenshot saved to {path:?}.");
                        std::process::exit(0);
                    }
                }

                let control_flow = if integration.should_close() {
                    EventResult::Exit
                } else if repaint_after.is_zero() {
                    EventResult::RepaintNext
                } else if let Some(repaint_after_instant) =
                    std::time::Instant::now().checked_add(repaint_after)
                {
                    // if repaint_after is something huge and can't be added to Instant,
                    // we will use `ControlFlow::Wait` instead.
                    // technically, this might lead to some weird corner cases where the user *WANTS*
                    // winit to use `WaitUntil(MAX_INSTANT)` explicitly. they can roll their own
                    // egui backend impl i guess.
                    EventResult::RepaintAt(repaint_after_instant)
                } else {
                    EventResult::Wait
                };

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

                if !self.is_focused {
                    // On Mac, a minimized Window uses up all CPU: https://github.com/emilk/egui/issues/325
                    // We can't know if we are minimized: https://github.com/rust-windowing/winit/issues/208
                    // But we know if we are focused (in foreground). When minimized, we are not focused.
                    // However, a user may want an egui with an animation in the background,
                    // so we still need to repaint quite fast.
                    crate::profile_scope!("bg_sleep");
                    std::thread::sleep(std::time::Duration::from_millis(10));
                }

                control_flow
            } else {
                EventResult::Wait
            }
        }

        fn on_event(
            &mut self,
            event_loop: &EventLoopWindowTarget<UserEvent>,
            event: &winit::event::Event<'_, UserEvent>,
        ) -> Result<EventResult> {
            Ok(match event {
                winit::event::Event::Resumed => {
                    // first resume event.
                    // we can actually move this outside of event loop.
                    // and just run the on_resume fn of gl_window
                    if self.running.is_none() {
                        self.init_run_state(event_loop)?;
                    } else {
                        // not the first resume event. create whatever you need.
                        self.running
                            .as_mut()
                            .unwrap()
                            .gl_window
                            .on_resume(event_loop)?;
                    }
                    EventResult::RepaintNow
                }
                winit::event::Event::Suspended => {
                    self.running.as_mut().unwrap().gl_window.on_suspend()?;

                    EventResult::Wait
                }

                winit::event::Event::WindowEvent { event, .. } => {
                    if let Some(running) = &mut self.running {
                        // 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) => {
                                self.is_focused = *new_focused;
                            }
                            winit::event::WindowEvent::Resized(physical_size) => {
                                repaint_asap = true;

                                // 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 physical_size.width > 0 && physical_size.height > 0 {
                                    running.gl_window.resize(*physical_size);
                                }
                            }
                            winit::event::WindowEvent::ScaleFactorChanged {
                                new_inner_size,
                                ..
                            } => {
                                repaint_asap = true;
                                running.gl_window.resize(**new_inner_size);
                            }
                            winit::event::WindowEvent::CloseRequested
                                if running.integration.should_close() =>
                            {
                                log::debug!("Received WindowEvent::CloseRequested");
                                return Ok(EventResult::Exit);
                            }
                            _ => {}
                        }

                        let event_response =
                            running.integration.on_event(running.app.as_mut(), event);

                        if running.integration.should_close() {
                            EventResult::Exit
                        } else if event_response.repaint {
                            if repaint_asap {
                                EventResult::RepaintNow
                            } else {
                                EventResult::RepaintNext
                            }
                        } else {
                            EventResult::Wait
                        }
                    } else {
                        EventResult::Wait
                    }
                }
                #[cfg(feature = "accesskit")]
                winit::event::Event::UserEvent(UserEvent::AccessKitActionRequest(
                    accesskit_winit::ActionRequestEvent { request, .. },
                )) => {
                    if let Some(running) = &mut self.running {
                        running
                            .integration
                            .on_accesskit_action_request(request.clone());
                        // As a form of user input, accessibility actions should
                        // lead to a repaint.
                        EventResult::RepaintNext
                    } else {
                        EventResult::Wait
                    }
                }
                _ => EventResult::Wait,
            })
        }
    }

    pub fn run_glow(
        app_name: &str,
        mut native_options: epi::NativeOptions,
        app_creator: epi::AppCreator,
    ) -> Result<()> {
        if native_options.run_and_return {
            with_event_loop(native_options, |event_loop, native_options| {
                let glow_eframe =
                    GlowWinitApp::new(event_loop, app_name, native_options, app_creator);
                run_and_return(event_loop, glow_eframe)
            })
        } else {
            let event_loop = create_event_loop_builder(&mut native_options).build();
            let glow_eframe = GlowWinitApp::new(&event_loop, app_name, native_options, app_creator);
            run_and_exit(event_loop, glow_eframe);
        }
    }
}

#[cfg(feature = "glow")]
pub use glow_integration::run_glow;
// ----------------------------------------------------------------------------

#[cfg(feature = "wgpu")]
mod wgpu_integration {
    use std::sync::Arc;

    use super::*;

    /// 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 WgpuWinitRunning {
        painter: egui_wgpu::winit::Painter,
        integration: epi_integration::EpiIntegration,
        app: Box<dyn epi::App>,
    }

    struct WgpuWinitApp {
        repaint_proxy: Arc<std::sync::Mutex<EventLoopProxy<UserEvent>>>,
        app_name: String,
        native_options: epi::NativeOptions,
        app_creator: Option<epi::AppCreator>,
        running: Option<WgpuWinitRunning>,

        /// Window surface state that's initialized when the app starts running via a Resumed event
        /// and on Android will also be destroyed if the application is paused.
        window: Option<winit::window::Window>,
        is_focused: bool,
    }

    impl WgpuWinitApp {
        fn new(
            event_loop: &EventLoop<UserEvent>,
            app_name: &str,
            native_options: epi::NativeOptions,
            app_creator: epi::AppCreator,
        ) -> Self {
            #[cfg(feature = "__screenshot")]
            assert!(
                std::env::var("EFRAME_SCREENSHOT_TO").is_err(),
                "EFRAME_SCREENSHOT_TO not yet implemented for wgpu backend"
            );

            Self {
                repaint_proxy: Arc::new(std::sync::Mutex::new(event_loop.create_proxy())),
                app_name: app_name.to_owned(),
                native_options,
                running: None,
                window: None,
                app_creator: Some(app_creator),
                is_focused: true,
            }
        }

        fn create_window(
            event_loop: &EventLoopWindowTarget<UserEvent>,
            storage: Option<&dyn epi::Storage>,
            title: &str,
            native_options: &NativeOptions,
        ) -> std::result::Result<winit::window::Window, winit::error::OsError> {
            let window_settings = epi_integration::load_window_settings(storage);
            let window_builder =
                epi_integration::window_builder(event_loop, title, native_options, window_settings);
            let window = window_builder.build(event_loop)?;
            epi_integration::apply_native_options_to_window(&window, native_options);
            Ok(window)
        }

        #[allow(unsafe_code)]
        fn set_window(
            &mut self,
            window: winit::window::Window,
        ) -> std::result::Result<(), egui_wgpu::WgpuError> {
            self.window = Some(window);
            if let Some(running) = &mut self.running {
                unsafe {
                    pollster::block_on(running.painter.set_window(self.window.as_ref()))?;
                }
            }
            Ok(())
        }

        #[allow(unsafe_code)]
        #[cfg(target_os = "android")]
        fn drop_window(&mut self) -> std::result::Result<(), egui_wgpu::WgpuError> {
            self.window = None;
            if let Some(running) = &mut self.running {
                unsafe {
                    pollster::block_on(running.painter.set_window(None))?;
                }
            }
            Ok(())
        }

        fn init_run_state(
            &mut self,
            event_loop: &EventLoopWindowTarget<UserEvent>,
            storage: Option<Box<dyn epi::Storage>>,
            window: winit::window::Window,
        ) -> std::result::Result<(), egui_wgpu::WgpuError> {
            #[allow(unsafe_code, unused_mut, unused_unsafe)]
            let painter = unsafe {
                let mut painter = egui_wgpu::winit::Painter::new(
                    self.native_options.wgpu_options.clone(),
                    self.native_options.multisampling.max(1) as _,
                    self.native_options.depth_buffer,
                    self.native_options.transparent,
                );
                pollster::block_on(painter.set_window(Some(&window)))?;
                painter
            };

            let wgpu_render_state = painter.render_state();

            let system_theme = system_theme(&window, &self.native_options);
            let mut integration = epi_integration::EpiIntegration::new(
                event_loop,
                painter.max_texture_side().unwrap_or(2048),
                &window,
                system_theme,
                &self.app_name,
                &self.native_options,
                storage,
                #[cfg(feature = "glow")]
                None,
                wgpu_render_state.clone(),
            );
            #[cfg(feature = "accesskit")]
            {
                integration.init_accesskit(&window, self.repaint_proxy.lock().unwrap().clone());
            }
            let theme = system_theme.unwrap_or(self.native_options.default_theme);
            integration.egui_ctx.set_visuals(theme.egui_visuals());

            window.set_ime_allowed(true);

            {
                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.after;
                        let frame_nr = info.current_frame_nr;
                        event_loop_proxy
                            .lock()
                            .unwrap()
                            .send_event(UserEvent::RequestRepaint { when, frame_nr })
                            .ok();
                    });
            }

            let app_creator = std::mem::take(&mut self.app_creator)
                .expect("Single-use AppCreator has unexpectedly already been taken");
            let mut app = app_creator(&epi::CreationContext {
                egui_ctx: integration.egui_ctx.clone(),
                integration_info: integration.frame.info(),
                storage: integration.frame.storage(),
                #[cfg(feature = "glow")]
                gl: None,
                wgpu_render_state,
            });

            if app.warm_up_enabled() {
                integration.warm_up(app.as_mut(), &window);
            }

            self.running = Some(WgpuWinitRunning {
                painter,
                integration,
                app,
            });
            self.window = Some(window);

            Ok(())
        }
    }

    impl WinitApp for WgpuWinitApp {
        fn frame_nr(&self) -> u64 {
            self.running
                .as_ref()
                .map_or(0, |r| r.integration.egui_ctx.frame_nr())
        }

        fn is_focused(&self) -> bool {
            self.is_focused
        }

        fn integration(&self) -> Option<&EpiIntegration> {
            self.running.as_ref().map(|r| &r.integration)
        }

        fn window(&self) -> Option<&winit::window::Window> {
            self.window.as_ref()
        }

        fn save_and_destroy(&mut self) {
            if let Some(mut running) = self.running.take() {
                if let Some(window) = &self.window {
                    running.integration.save(running.app.as_mut(), window);
                }

                #[cfg(feature = "glow")]
                running.app.on_exit(None);

                #[cfg(not(feature = "glow"))]
                running.app.on_exit();

                running.painter.destroy();
            }
        }

        fn run_ui_and_paint(&mut self) -> EventResult {
            if let (Some(running), Some(window)) = (&mut self.running, &self.window) {
                #[cfg(feature = "puffin")]
                puffin::GlobalProfiler::lock().new_frame();
                crate::profile_scope!("frame");

                let WgpuWinitRunning {
                    app,
                    integration,
                    painter,
                } = running;

                let egui::FullOutput {
                    platform_output,
                    repaint_after,
                    textures_delta,
                    shapes,
                } = integration.update(app.as_mut(), window);

                integration.handle_platform_output(window, platform_output);

                let clipped_primitives = {
                    crate::profile_scope!("tessellate");
                    integration.egui_ctx.tessellate(shapes)
                };

                let screenshot_requested = &mut integration.frame.output.screenshot_requested;

                let screenshot = painter.paint_and_update_textures(
                    integration.egui_ctx.pixels_per_point(),
                    app.clear_color(&integration.egui_ctx.style().visuals),
                    &clipped_primitives,
                    &textures_delta,
                    *screenshot_requested,
                );
                *screenshot_requested = false;
                integration.frame.screenshot.set(screenshot);

                integration.post_rendering(app.as_mut(), window);
                integration.post_present(window);

                let control_flow = if integration.should_close() {
                    EventResult::Exit
                } else if repaint_after.is_zero() {
                    EventResult::RepaintNext
                } else if let Some(repaint_after_instant) =
                    std::time::Instant::now().checked_add(repaint_after)
                {
                    // if repaint_after is something huge and can't be added to Instant,
                    // we will use `ControlFlow::Wait` instead.
                    // technically, this might lead to some weird corner cases where the user *WANTS*
                    // winit to use `WaitUntil(MAX_INSTANT)` explicitly. they can roll their own
                    // egui backend impl i guess.
                    EventResult::RepaintAt(repaint_after_instant)
                } else {
                    EventResult::Wait
                };

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

                if !self.is_focused {
                    // On Mac, a minimized Window uses up all CPU: https://github.com/emilk/egui/issues/325
                    // We can't know if we are minimized: https://github.com/rust-windowing/winit/issues/208
                    // But we know if we are focused (in foreground). When minimized, we are not focused.
                    // However, a user may want an egui with an animation in the background,
                    // so we still need to repaint quite fast.
                    crate::profile_scope!("bg_sleep");
                    std::thread::sleep(std::time::Duration::from_millis(10));
                }

                control_flow
            } else {
                EventResult::Wait
            }
        }

        fn on_event(
            &mut self,
            event_loop: &EventLoopWindowTarget<UserEvent>,
            event: &winit::event::Event<'_, UserEvent>,
        ) -> Result<EventResult> {
            Ok(match event {
                winit::event::Event::Resumed => {
                    if let Some(running) = &self.running {
                        if self.window.is_none() {
                            let window = Self::create_window(
                                event_loop,
                                running.integration.frame.storage(),
                                &self.app_name,
                                &self.native_options,
                            )?;
                            self.set_window(window)?;
                        }
                    } else {
                        let storage = epi_integration::create_storage(&self.app_name);
                        let window = Self::create_window(
                            event_loop,
                            storage.as_deref(),
                            &self.app_name,
                            &self.native_options,
                        )?;
                        self.init_run_state(event_loop, storage, window)?;
                    }
                    EventResult::RepaintNow
                }
                winit::event::Event::Suspended => {
                    #[cfg(target_os = "android")]
                    self.drop_window()?;
                    EventResult::Wait
                }

                winit::event::Event::WindowEvent { event, .. } => {
                    if let Some(running) = &mut self.running {
                        // 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) => {
                                self.is_focused = *new_focused;
                            }
                            winit::event::WindowEvent::Resized(physical_size) => {
                                repaint_asap = true;

                                // 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 physical_size.width > 0 && physical_size.height > 0 {
                                    running.painter.on_window_resized(
                                        physical_size.width,
                                        physical_size.height,
                                    );
                                }
                            }
                            winit::event::WindowEvent::ScaleFactorChanged {
                                new_inner_size,
                                ..
                            } => {
                                repaint_asap = true;
                                running
                                    .painter
                                    .on_window_resized(new_inner_size.width, new_inner_size.height);
                            }
                            winit::event::WindowEvent::CloseRequested
                                if running.integration.should_close() =>
                            {
                                log::debug!("Received WindowEvent::CloseRequested");
                                return Ok(EventResult::Exit);
                            }
                            _ => {}
                        };

                        let event_response =
                            running.integration.on_event(running.app.as_mut(), event);
                        if running.integration.should_close() {
                            EventResult::Exit
                        } else if event_response.repaint {
                            if repaint_asap {
                                EventResult::RepaintNow
                            } else {
                                EventResult::RepaintNext
                            }
                        } else {
                            EventResult::Wait
                        }
                    } else {
                        EventResult::Wait
                    }
                }
                #[cfg(feature = "accesskit")]
                winit::event::Event::UserEvent(UserEvent::AccessKitActionRequest(
                    accesskit_winit::ActionRequestEvent { request, .. },
                )) => {
                    if let Some(running) = &mut self.running {
                        running
                            .integration
                            .on_accesskit_action_request(request.clone());
                        // As a form of user input, accessibility actions should
                        // lead to a repaint.
                        EventResult::RepaintNext
                    } else {
                        EventResult::Wait
                    }
                }
                _ => EventResult::Wait,
            })
        }
    }

    pub fn run_wgpu(
        app_name: &str,
        mut native_options: epi::NativeOptions,
        app_creator: epi::AppCreator,
    ) -> Result<()> {
        if native_options.run_and_return {
            with_event_loop(native_options, |event_loop, native_options| {
                let wgpu_eframe =
                    WgpuWinitApp::new(event_loop, app_name, native_options, app_creator);
                run_and_return(event_loop, wgpu_eframe)
            })
        } else {
            let event_loop = create_event_loop_builder(&mut native_options).build();
            let wgpu_eframe = WgpuWinitApp::new(&event_loop, app_name, native_options, app_creator);
            run_and_exit(event_loop, wgpu_eframe);
        }
    }
}

#[cfg(feature = "wgpu")]
pub use wgpu_integration::run_wgpu;

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

fn system_theme(window: &winit::window::Window, options: &NativeOptions) -> Option<crate::Theme> {
    if options.follow_system_theme {
        window
            .theme()
            .map(super::epi_integration::theme_from_winit_theme)
    } else {
        None
    }
}

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

fn extremely_far_future() -> std::time::Instant {
    std::time::Instant::now() + std::time::Duration::from_secs(10_000_000_000)
}
