//! 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::Duration;
use std::time::Instant;

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

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

#[derive(Debug)]
pub struct RequestRepaintEvent;

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

pub use epi::NativeOptions;

#[derive(Debug)]
enum EventResult {
    Wait,
    RepaintAsap,
    RepaintAt(Instant),
    Exit,
}

trait WinitApp {
    fn is_focused(&self) -> bool;
    fn integration(&self) -> Option<&EpiIntegration>;
    fn window(&self) -> Option<&winit::window::Window>;
    fn save_and_destroy(&mut self);
    fn paint(&mut self) -> EventResult;
    fn on_event(
        &mut self,
        event_loop: &EventLoopWindowTarget<RequestRepaintEvent>,
        event: &winit::event::Event<'_, RequestRepaintEvent>,
    ) -> EventResult;
}

fn create_event_loop_builder(
    native_options: &mut epi::NativeOptions,
) -> EventLoopBuilder<RequestRepaintEvent> {
    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(
    mut native_options: epi::NativeOptions,
    f: impl FnOnce(&mut EventLoop<RequestRepaintEvent>, NativeOptions),
) {
    use std::cell::RefCell;
    thread_local!(static EVENT_LOOP: RefCell<Option<EventLoop<RequestRepaintEvent>>> = 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<RequestRepaintEvent>, mut winit_app: impl WinitApp) {
    use winit::platform::run_return::EventLoopExtRunReturn as _;

    tracing::debug!("event_loop.run_return");

    let mut next_repaint_time = Instant::now();

    event_loop.run_return(|event, event_loop, control_flow| {
        let event_result = match &event {
            winit::event::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 = Instant::now() + Duration::from_secs(1_000_000_000);
                winit_app.paint()
            }
            winit::event::Event::RedrawRequested(_) if !cfg!(windows) => {
                next_repaint_time = Instant::now() + Duration::from_secs(1_000_000_000);
                winit_app.paint()
            }

            winit::event::Event::UserEvent(RequestRepaintEvent)
            | winit::event::Event::NewEvents(winit::event::StartCause::ResumeTimeReached {
                ..
            }) => EventResult::RepaintAsap,

            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 => winit_app.on_event(event_loop, event),
        };

        match event_result {
            EventResult::Wait => {}
            EventResult::RepaintAsap => {
                tracing::debug!("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 => {
                *control_flow = ControlFlow::Exit;
                return;
            }
        }

        *control_flow = match next_repaint_time.checked_duration_since(Instant::now()) {
            None => {
                if let Some(window) = winit_app.window() {
                    window.request_redraw();
                }
                next_repaint_time = Instant::now() + Duration::from_secs(1_000_000_000);
                ControlFlow::Poll
            }
            Some(time_until_next_repaint) => {
                ControlFlow::WaitUntil(Instant::now() + time_until_next_repaint)
            }
        }
    });

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

    winit_app.save_and_destroy();

    drop(winit_app);

    // Needed to clean the event_loop:
    event_loop.run_return(|_, _, control_flow| {
        control_flow.set_exit();
    });
}

fn run_and_exit(
    event_loop: EventLoop<RequestRepaintEvent>,
    mut winit_app: impl WinitApp + 'static,
) -> ! {
    tracing::debug!("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 => 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 = Instant::now() + Duration::from_secs(1_000_000_000);
                winit_app.paint()
            }
            winit::event::Event::RedrawRequested(_) if !cfg!(windows) => {
                next_repaint_time = Instant::now() + Duration::from_secs(1_000_000_000);
                winit_app.paint()
            }

            winit::event::Event::UserEvent(RequestRepaintEvent)
            | winit::event::Event::NewEvents(winit::event::StartCause::ResumeTimeReached {
                ..
            }) => EventResult::RepaintAsap,

            event => winit_app.on_event(event_loop, &event),
        };

        match event_result {
            EventResult::Wait => {}
            EventResult::RepaintAsap => {
                next_repaint_time = Instant::now();
            }
            EventResult::RepaintAt(repaint_time) => {
                next_repaint_time = next_repaint_time.min(repaint_time);
            }
            EventResult::Exit => {
                tracing::debug!("Quitting…");
                winit_app.save_and_destroy();
                #[allow(clippy::exit)]
                std::process::exit(0);
            }
        }

        *control_flow = match next_repaint_time.checked_duration_since(Instant::now()) {
            None => {
                if let Some(window) = winit_app.window() {
                    window.request_redraw();
                }
                ControlFlow::Poll
            }
            Some(time_until_next_repaint) => {
                ControlFlow::WaitUntil(Instant::now() + time_until_next_repaint)
            }
        }
    })
}

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

    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: glutin::WindowedContext<glutin::PossiblyCurrent>,
    }

    struct GlowWinitApp {
        repaint_proxy: Arc<egui::mutex::Mutex<EventLoopProxy<RequestRepaintEvent>>>,
        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<RequestRepaintEvent>,
            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<RequestRepaintEvent>,
            storage: Option<&dyn epi::Storage>,
            title: &String,
            native_options: &NativeOptions,
        ) -> (
            glutin::WindowedContext<glutin::PossiblyCurrent>,
            glow::Context,
        ) {
            crate::profile_function!();

            use crate::HardwareAcceleration;

            let hardware_acceleration = match native_options.hardware_acceleration {
                HardwareAcceleration::Required => Some(true),
                HardwareAcceleration::Preferred => None,
                HardwareAcceleration::Off => Some(false),
            };
            let window_settings = epi_integration::load_window_settings(storage);

            let window_builder =
                epi_integration::window_builder(native_options, &window_settings).with_title(title);

            let gl_window = unsafe {
                glutin::ContextBuilder::new()
                    .with_hardware_acceleration(hardware_acceleration)
                    .with_depth_buffer(native_options.depth_buffer)
                    .with_multisampling(native_options.multisampling)
                    .with_srgb(true)
                    .with_stencil_buffer(native_options.stencil_buffer)
                    .with_vsync(native_options.vsync)
                    .build_windowed(window_builder, event_loop)
                    .unwrap()
                    .make_current()
                    .unwrap()
            };

            let gl =
                unsafe { glow::Context::from_loader_function(|s| gl_window.get_proc_address(s)) };

            (gl_window, gl)
        }

        fn init_run_state(&mut self, event_loop: &EventLoopWindowTarget<RequestRepaintEvent>) {
            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(), None, "", self.native_options.shader_version)
                    .unwrap_or_else(|error| panic!("some OpenGL error occurred {}\n", error));

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

            {
                let event_loop_proxy = self.repaint_proxy.clone();
                integration.egui_ctx.set_request_repaint_callback(move || {
                    event_loop_proxy.lock().send_event(RequestRepaintEvent).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,
            });
        }
    }

    impl WinitApp for GlowWinitApp {
        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(running) = &mut self.running {
                running
                    .integration
                    .save(running.app.as_mut(), running.gl_window.window());
                running.app.on_exit(Some(&running.gl));
                running.painter.destroy();
            }
        }

        fn 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,
                );

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

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

                let control_flow = if integration.should_close() {
                    EventResult::Exit
                } else if repaint_after.is_zero() {
                    EventResult::RepaintAsap
                } 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<RequestRepaintEvent>,
            event: &winit::event::Event<'_, RequestRepaintEvent>,
        ) -> EventResult {
            match event {
                winit::event::Event::Resumed => {
                    if self.running.is_none() {
                        self.init_run_state(event_loop);
                    }
                    EventResult::RepaintAsap
                }
                winit::event::Event::Suspended => {
                    #[cfg(target_os = "android")]
                    {
                        tracing::error!("Suspended app can't destroy Window surface state with current Egui Glow backend (undefined behaviour)");
                        // Instead of destroying everything which we _know_ we can't re-create
                        // we instead currently just try our luck with not destroying anything.
                        //
                        // When the application resumes then it will get a new `SurfaceView` but
                        // we have no practical way currently of creating a new EGL surface
                        // via the Glutin API while keeping the GL context and the rest of
                        // our app state. This will likely result in a black screen or
                        // frozen screen.
                        //
                        //self.running = None;
                    }
                    EventResult::Wait
                }

                winit::event::Event::WindowEvent { event, .. } => {
                    if let Some(running) = &mut self.running {
                        match &event {
                            winit::event::WindowEvent::Focused(new_focused) => {
                                self.is_focused = *new_focused;
                            }
                            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 physical_size.width > 0 && physical_size.height > 0 {
                                    running.gl_window.resize(*physical_size);
                                }
                            }
                            winit::event::WindowEvent::ScaleFactorChanged {
                                new_inner_size,
                                ..
                            } => {
                                running.gl_window.resize(**new_inner_size);
                            }
                            winit::event::WindowEvent::CloseRequested
                                if running.integration.should_close() =>
                            {
                                return 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 {
                            EventResult::RepaintAsap
                        } else {
                            EventResult::Wait
                        }
                    } else {
                        EventResult::Wait
                    }
                }
                _ => EventResult::Wait,
            }
        }
    }

    pub fn run_glow(
        app_name: &str,
        mut native_options: epi::NativeOptions,
        app_creator: epi::AppCreator,
    ) {
        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<'static>,
        integration: epi_integration::EpiIntegration,
        app: Box<dyn epi::App>,
    }

    struct WgpuWinitApp {
        repaint_proxy: Arc<std::sync::Mutex<EventLoopProxy<RequestRepaintEvent>>>,
        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<RequestRepaintEvent>,
            app_name: &str,
            native_options: epi::NativeOptions,
            app_creator: epi::AppCreator,
        ) -> Self {
            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<RequestRepaintEvent>,
            storage: Option<&dyn epi::Storage>,
            title: &String,
            native_options: &NativeOptions,
        ) -> winit::window::Window {
            let window_settings = epi_integration::load_window_settings(storage);
            epi_integration::window_builder(native_options, &window_settings)
                .with_title(title)
                .build(event_loop)
                .unwrap()
        }

        #[allow(unsafe_code)]
        fn set_window(&mut self, window: winit::window::Window) {
            self.window = Some(window);
            if let Some(running) = &mut self.running {
                unsafe {
                    running.painter.set_window(self.window.as_ref());
                }
            }
        }

        #[allow(unsafe_code)]
        #[cfg(target_os = "android")]
        fn drop_window(&mut self) {
            self.window = None;
            if let Some(running) = &mut self.running {
                unsafe {
                    running.painter.set_window(None);
                }
            }
        }

        fn init_run_state(
            &mut self,
            event_loop: &EventLoopWindowTarget<RequestRepaintEvent>,
            storage: Option<Box<dyn epi::Storage>>,
            window: winit::window::Window,
        ) {
            let mut limits = wgpu::Limits::downlevel_webgl2_defaults();
            if self.native_options.depth_buffer > 0 {
                // When using a depth buffer, we have to be able to create a texture large enough for the entire surface.
                limits.max_texture_dimension_2d = 8192;
            }

            #[allow(unsafe_code, unused_mut, unused_unsafe)]
            let painter = unsafe {
                let mut painter = egui_wgpu::winit::Painter::new(
                    wgpu::Backends::PRIMARY | wgpu::Backends::GL,
                    wgpu::PowerPreference::HighPerformance,
                    wgpu::DeviceDescriptor {
                        label: None,
                        features: wgpu::Features::default(),
                        limits,
                    },
                    wgpu::PresentMode::Fifo,
                    self.native_options.multisampling.max(1) as _,
                    self.native_options.depth_buffer,
                );
                painter.set_window(Some(&window));
                painter
            };

            let wgpu_render_state = painter.render_state();

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

            {
                let event_loop_proxy = self.repaint_proxy.clone();
                integration.egui_ctx.set_request_repaint_callback(move || {
                    event_loop_proxy
                        .lock()
                        .unwrap()
                        .send_event(RequestRepaintEvent)
                        .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);
        }
    }

    impl WinitApp for WgpuWinitApp {
        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(running) = &mut self.running {
                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 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)
                };

                painter.paint_and_update_textures(
                    integration.egui_ctx.pixels_per_point(),
                    app.clear_color(&integration.egui_ctx.style().visuals),
                    &clipped_primitives,
                    &textures_delta,
                );

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

                let control_flow = if integration.should_close() {
                    EventResult::Exit
                } else if repaint_after.is_zero() {
                    EventResult::RepaintAsap
                } 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<RequestRepaintEvent>,
            event: &winit::event::Event<'_, RequestRepaintEvent>,
        ) -> EventResult {
            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::RepaintAsap
                }
                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 {
                        match &event {
                            winit::event::WindowEvent::Focused(new_focused) => {
                                self.is_focused = *new_focused;
                            }
                            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 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,
                                ..
                            } => {
                                running
                                    .painter
                                    .on_window_resized(new_inner_size.width, new_inner_size.height);
                            }
                            winit::event::WindowEvent::CloseRequested
                                if running.integration.should_close() =>
                            {
                                return 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 {
                            EventResult::RepaintAsap
                        } else {
                            EventResult::Wait
                        }
                    } else {
                        EventResult::Wait
                    }
                }
                _ => EventResult::Wait,
            }
        }
    }

    pub fn run_wgpu(
        app_name: &str,
        mut native_options: epi::NativeOptions,
        app_creator: epi::AppCreator,
    ) {
        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;