//! 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};

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

#[derive(Debug)]
struct RequestRepaintEvent;

#[cfg(feature = "glow")]
#[allow(unsafe_code)]
fn create_display(
    native_options: &NativeOptions,
    window_builder: winit::window::WindowBuilder,
    event_loop: &EventLoop<RequestRepaintEvent>,
) -> (
    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 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)
}

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

pub use epi::NativeOptions;

enum EventResult {
    Wait,
    RepaintAsap,
    RepaintAt(Instant),
    Exit,
}

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

/// 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(f: impl FnOnce(&mut EventLoop<RequestRepaintEvent>)) {
    use std::cell::RefCell;
    thread_local!(static EVENT_LOOP: RefCell<EventLoop<RequestRepaintEvent>> = RefCell::new(winit::event_loop::EventLoopBuilder::with_user_event().build()));

    EVENT_LOOP.with(|event_loop| {
        f(&mut *event_loop.borrow_mut());
    });
}

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, _, 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 window_id != winit_app.window().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),
        };

        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 => {
                *control_flow = ControlFlow::Exit;
                return;
            }
        }

        *control_flow = match next_repaint_time.checked_duration_since(Instant::now()) {
            None => {
                winit_app.window().request_redraw();
                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, _, 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),
        };

        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 => {
                winit_app.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::*;

    struct GlowWinitApp {
        gl_window: glutin::WindowedContext<glutin::PossiblyCurrent>,
        gl: Arc<glow::Context>,
        painter: egui_glow::Painter,
        integration: epi_integration::EpiIntegration,
        app: Box<dyn epi::App>,
        is_focused: bool,
    }

    impl GlowWinitApp {
        fn new(
            event_loop: &EventLoop<RequestRepaintEvent>,
            app_name: &str,
            native_options: &epi::NativeOptions,
            app_creator: epi::AppCreator,
        ) -> Self {
            let storage = epi_integration::create_storage(app_name);
            let window_settings = epi_integration::load_window_settings(storage.as_deref());

            let window_builder = epi_integration::window_builder(native_options, &window_settings)
                .with_title(app_name);
            let (gl_window, gl) = create_display(native_options, window_builder, event_loop);
            let gl = Arc::new(gl);

            let painter = egui_glow::Painter::new(gl.clone(), None, "")
                .unwrap_or_else(|error| panic!("some OpenGL error occurred {}\n", error));

            let system_theme = 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(native_options.default_theme);
            integration.egui_ctx.set_visuals(theme.egui_visuals());

            {
                let event_loop_proxy = egui::mutex::Mutex::new(event_loop.create_proxy());
                integration.egui_ctx.set_request_repaint_callback(move || {
                    event_loop_proxy.lock().send_event(RequestRepaintEvent).ok();
                });
            }

            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 {
                gl_window,
                gl,
                painter,
                integration,
                app,
                is_focused: true,
            }
        }
    }

    impl WinitApp for GlowWinitApp {
        fn is_focused(&self) -> bool {
            self.is_focused
        }

        fn integration(&self) -> &EpiIntegration {
            &self.integration
        }

        fn window(&self) -> &winit::window::Window {
            self.gl_window.window()
        }

        fn save_and_destroy(&mut self) {
            self.integration
                .save(&mut *self.app, self.gl_window.window());
            self.app.on_exit(Some(&self.gl));
            self.painter.destroy();
        }

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

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

        fn on_event(&mut self, event: winit::event::Event<'_, RequestRepaintEvent>) -> EventResult {
            match event {
                winit::event::Event::WindowEvent { event, .. } => {
                    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 {
                                self.gl_window.resize(*physical_size);
                            }
                        }
                        winit::event::WindowEvent::ScaleFactorChanged {
                            new_inner_size, ..
                        } => {
                            self.gl_window.resize(**new_inner_size);
                        }
                        winit::event::WindowEvent::CloseRequested
                            if self.integration.should_close() =>
                        {
                            return EventResult::Exit
                        }
                        _ => {}
                    }

                    self.integration.on_event(self.app.as_mut(), &event);

                    if self.integration.should_close() {
                        EventResult::Exit
                    } else {
                        // TODO(emilk): ask egui if the event warrants a repaint
                        EventResult::RepaintAsap
                    }
                }
                _ => EventResult::Wait,
            }
        }
    }

    pub fn run_glow(
        app_name: &str,
        native_options: &epi::NativeOptions,
        app_creator: epi::AppCreator,
    ) {
        if native_options.run_and_return {
            with_event_loop(|event_loop| {
                let glow_eframe =
                    GlowWinitApp::new(event_loop, app_name, native_options, app_creator);
                run_and_return(event_loop, glow_eframe);
            });
        } else {
            let event_loop = winit::event_loop::EventLoopBuilder::with_user_event().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 super::*;

    struct WgpuWinitApp {
        window: winit::window::Window,
        painter: egui_wgpu::winit::Painter<'static>,
        integration: epi_integration::EpiIntegration,
        app: Box<dyn epi::App>,
        is_focused: bool,
    }

    impl WgpuWinitApp {
        fn new(
            event_loop: &EventLoop<RequestRepaintEvent>,
            app_name: &str,
            native_options: &epi::NativeOptions,
            app_creator: epi::AppCreator,
        ) -> Self {
            let storage = epi_integration::create_storage(app_name);
            let window_settings = epi_integration::load_window_settings(storage.as_deref());

            let window = epi_integration::window_builder(native_options, &window_settings)
                .with_title(app_name)
                .build(event_loop)
                .unwrap();

            // SAFETY: `window` must outlive `painter`.
            #[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::Limits::default(),
                    },
                    wgpu::PresentMode::Fifo,
                    native_options.multisampling.max(1) as _,
                );
                #[cfg(not(target_os = "android"))]
                painter.set_window(Some(&window));
                painter
            };

            let wgpu_render_state = painter.render_state();

            let system_theme = 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(native_options.default_theme);
            integration.egui_ctx.set_visuals(theme.egui_visuals());

            {
                let event_loop_proxy = egui::mutex::Mutex::new(event_loop.create_proxy());
                integration.egui_ctx.set_request_repaint_callback(move || {
                    event_loop_proxy.lock().send_event(RequestRepaintEvent).ok();
                });
            }

            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 {
                window,
                painter,
                integration,
                app,
                is_focused: true,
            }
        }
    }

    impl WinitApp for WgpuWinitApp {
        fn is_focused(&self) -> bool {
            self.is_focused
        }

        fn integration(&self) -> &EpiIntegration {
            &self.integration
        }

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

        fn save_and_destroy(&mut self) {
            self.integration.save(&mut *self.app, &self.window);

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

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

            self.painter.destroy();
        }

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

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

            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
        }

        fn on_event(&mut self, event: winit::event::Event<'_, RequestRepaintEvent>) -> EventResult {
            match event {
                #[cfg(target_os = "android")]
                winit::event::Event::Resumed => unsafe {
                    self.painter.set_window(Some(&self.window));
                    EventResult::RepaintAsap
                },
                #[cfg(target_os = "android")]
                winit::event::Event::Suspended => unsafe {
                    self.painter.set_window(None);
                    EventResult::Wait
                },

                winit::event::Event::WindowEvent { event, .. } => {
                    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 {
                                self.painter
                                    .on_window_resized(physical_size.width, physical_size.height);
                            }
                        }
                        winit::event::WindowEvent::ScaleFactorChanged {
                            new_inner_size, ..
                        } => {
                            self.painter
                                .on_window_resized(new_inner_size.width, new_inner_size.height);
                        }
                        winit::event::WindowEvent::CloseRequested
                            if self.integration.should_close() =>
                        {
                            return EventResult::Exit
                        }
                        _ => {}
                    };

                    self.integration.on_event(self.app.as_mut(), &event);
                    if self.integration.should_close() {
                        EventResult::Exit
                    } else {
                        // TODO(emilk): ask egui if the event warrants a repaint
                        EventResult::RepaintAsap
                    }
                }
                _ => EventResult::Wait,
            }
        }
    }

    pub fn run_wgpu(
        app_name: &str,
        native_options: &epi::NativeOptions,
        app_creator: epi::AppCreator,
    ) {
        if native_options.run_and_return {
            with_event_loop(|event_loop| {
                let wgpu_eframe =
                    WgpuWinitApp::new(event_loop, app_name, native_options, app_creator);
                run_and_return(event_loop, wgpu_eframe);
            });
        } else {
            let event_loop = winit::event_loop::EventLoopBuilder::with_user_event().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;