//! Create interactive, native cross-platform applications for WGPU.
mod state;
mod window_manager;

pub use state::State;

use crate::conversion;
use crate::core;
use crate::core::mouse;
use crate::core::renderer;
use crate::core::widget::operation;
use crate::core::window;
use crate::core::Size;
use crate::futures::futures::channel::mpsc;
use crate::futures::futures::{task, Future, StreamExt};
use crate::futures::{Executor, Runtime, Subscription};
use crate::graphics::{compositor, Compositor};
use crate::multi_window::window_manager::WindowManager;
use crate::runtime::command::{self, Command};
use crate::runtime::multi_window::Program;
use crate::runtime::user_interface::{self, UserInterface};
use crate::runtime::Debug;
use crate::style::application::StyleSheet;
use crate::{Clipboard, Error, Proxy, Settings};

use std::collections::HashMap;
use std::mem::ManuallyDrop;
use std::sync::Arc;
use std::time::Instant;

/// An interactive, native, cross-platform, multi-windowed application.
///
/// This trait is the main entrypoint of multi-window Iced. Once implemented, you can run
/// your GUI application by simply calling [`run`]. It will run in
/// its own window.
///
/// An [`Application`] can execute asynchronous actions by returning a
/// [`Command`] in some of its methods.
///
/// When using an [`Application`] with the `debug` feature enabled, a debug view
/// can be toggled by pressing `F12`.
pub trait Application: Program
where
    Self::Theme: StyleSheet,
{
    /// The data needed to initialize your [`Application`].
    type Flags;

    /// Initializes the [`Application`] with the flags provided to
    /// [`run`] as part of the [`Settings`].
    ///
    /// Here is where you should return the initial state of your app.
    ///
    /// Additionally, you can return a [`Command`] if you need to perform some
    /// async action in the background on startup. This is useful if you want to
    /// load state from a file, perform an initial HTTP request, etc.
    fn new(flags: Self::Flags) -> (Self, Command<Self::Message>);

    /// Returns the current title of the [`Application`].
    ///
    /// This title can be dynamic! The runtime will automatically update the
    /// title of your application when necessary.
    fn title(&self, window: window::Id) -> String;

    /// Returns the current `Theme` of the [`Application`].
    fn theme(&self, window: window::Id) -> Self::Theme;

    /// Returns the `Style` variation of the `Theme`.
    fn style(&self) -> <Self::Theme as StyleSheet>::Style {
        Default::default()
    }

    /// Returns the event `Subscription` for the current state of the
    /// application.
    ///
    /// The messages produced by the `Subscription` will be handled by
    /// [`update`](#tymethod.update).
    ///
    /// A `Subscription` will be kept alive as long as you keep returning it!
    ///
    /// By default, it returns an empty subscription.
    fn subscription(&self) -> Subscription<Self::Message> {
        Subscription::none()
    }

    /// Returns the scale factor of the window of the [`Application`].
    ///
    /// It can be used to dynamically control the size of the UI at runtime
    /// (i.e. zooming).
    ///
    /// For instance, a scale factor of `2.0` will make widgets twice as big,
    /// while a scale factor of `0.5` will shrink them to half their size.
    ///
    /// By default, it returns `1.0`.
    #[allow(unused_variables)]
    fn scale_factor(&self, window: window::Id) -> f64 {
        1.0
    }
}

/// Runs an [`Application`] with an executor, compositor, and the provided
/// settings.
pub fn run<A, E, C>(
    settings: Settings<A::Flags>,
    compositor_settings: C::Settings,
) -> Result<(), Error>
where
    A: Application + 'static,
    E: Executor + 'static,
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: StyleSheet,
{
    use winit::event_loop::EventLoopBuilder;

    let mut debug = Debug::new();
    debug.startup_started();

    let event_loop = EventLoopBuilder::with_user_event()
        .build()
        .expect("Create event loop");

    let proxy = event_loop.create_proxy();

    let runtime = {
        let proxy = Proxy::new(event_loop.create_proxy());
        let executor = E::new().map_err(Error::ExecutorCreationFailed)?;

        Runtime::new(executor, proxy)
    };

    let (application, init_command) = {
        let flags = settings.flags;

        runtime.enter(|| A::new(flags))
    };

    let should_main_be_visible = settings.window.visible;
    let exit_on_close_request = settings.window.exit_on_close_request;

    let builder = conversion::window_settings(
        settings.window,
        &application.title(window::Id::MAIN),
        event_loop.primary_monitor(),
        settings.id,
    )
    .with_visible(false);

    log::info!("Window builder: {:#?}", builder);

    let main_window = Arc::new(
        builder
            .build(&event_loop)
            .map_err(Error::WindowCreationFailed)?,
    );

    #[cfg(target_arch = "wasm32")]
    {
        use winit::platform::web::WindowExtWebSys;

        let canvas = main_window.canvas();

        let window = web_sys::window().unwrap();
        let document = window.document().unwrap();
        let body = document.body().unwrap();

        let target = target.and_then(|target| {
            body.query_selector(&format!("#{}", target))
                .ok()
                .unwrap_or(None)
        });

        match target {
            Some(node) => {
                let _ = node
                    .replace_with_with_node_1(&canvas)
                    .expect(&format!("Could not replace #{}", node.id()));
            }
            None => {
                let _ = body
                    .append_child(&canvas)
                    .expect("Append canvas to HTML body");
            }
        };
    }

    let mut compositor = C::new(compositor_settings, main_window.clone())?;

    let mut window_manager = WindowManager::new();
    let _ = window_manager.insert(
        window::Id::MAIN,
        main_window,
        &application,
        &mut compositor,
        exit_on_close_request,
    );

    let (mut event_sender, event_receiver) = mpsc::unbounded();
    let (control_sender, mut control_receiver) = mpsc::unbounded();

    let mut instance = Box::pin(run_instance::<A, E, C>(
        application,
        compositor,
        runtime,
        proxy,
        debug,
        event_receiver,
        control_sender,
        init_command,
        window_manager,
        should_main_be_visible,
    ));

    let mut context = task::Context::from_waker(task::noop_waker_ref());

    let process_event = move |event, event_loop: &winit::event_loop::EventLoopWindowTarget<_>| {
        if event_loop.exiting() {
            return;
        }

        event_sender
            .start_send(Event::EventLoopAwakened(event))
            .expect("Send event");

        loop {
            let poll = instance.as_mut().poll(&mut context);

            match poll {
                task::Poll::Pending => match control_receiver.try_next() {
                    Ok(Some(control)) => match control {
                        Control::ChangeFlow(flow) => {
                            use winit::event_loop::ControlFlow;

                            match (event_loop.control_flow(), flow) {
                                (
                                    ControlFlow::WaitUntil(current),
                                    ControlFlow::WaitUntil(new),
                                ) if new < current => {}
                                (
                                    ControlFlow::WaitUntil(target),
                                    ControlFlow::Wait,
                                ) if target > Instant::now() => {}
                                _ => {
                                    event_loop.set_control_flow(flow);
                                }
                            }
                        }
                        Control::CreateWindow {
                            id,
                            settings,
                            title,
                            monitor,
                        } => {
                            let exit_on_close_request =
                                settings.exit_on_close_request;

                            let window = conversion::window_settings(
                                settings, &title, monitor, None,
                            )
                            .build(event_loop)
                            .expect("Failed to build window");

                            event_sender
                                .start_send(Event::WindowCreated {
                                    id,
                                    window,
                                    exit_on_close_request,
                                })
                                .expect("Send event");
                        }
                        Control::Exit => {
                            event_loop.exit();
                        }
                    },
                    _ => {
                        break;
                    }
                },
                task::Poll::Ready(_) => {
                    event_loop.exit();
                    break;
                }
            };
        }
    };

    #[cfg(not(target_os = "windows"))]
    let _ = event_loop.run(process_event);

    // TODO: Remove when unnecessary
    // On Windows, we emulate an `AboutToWait` event after every `Resized` event
    // since the event loop does not resume during resize interaction.
    // More details: https://github.com/rust-windowing/winit/issues/3272
    #[cfg(target_os = "windows")]
    {
        let mut process_event = process_event;

        let _ = event_loop.run(move |event, event_loop| {
            if matches!(
                event,
                winit::event::Event::WindowEvent {
                    event: winit::event::WindowEvent::Resized(_)
                        | winit::event::WindowEvent::Moved(_),
                    ..
                }
            ) {
                process_event(event, event_loop);
                process_event(winit::event::Event::AboutToWait, event_loop);
            } else {
                process_event(event, event_loop);
            }
        });
    }

    Ok(())
}

enum Event<Message: 'static> {
    WindowCreated {
        id: window::Id,
        window: winit::window::Window,
        exit_on_close_request: bool,
    },
    EventLoopAwakened(winit::event::Event<Message>),
}

enum Control {
    ChangeFlow(winit::event_loop::ControlFlow),
    Exit,
    CreateWindow {
        id: window::Id,
        settings: window::Settings,
        title: String,
        monitor: Option<winit::monitor::MonitorHandle>,
    },
}

async fn run_instance<A, E, C>(
    mut application: A,
    mut compositor: C,
    mut runtime: Runtime<E, Proxy<A::Message>, A::Message>,
    mut proxy: winit::event_loop::EventLoopProxy<A::Message>,
    mut debug: Debug,
    mut event_receiver: mpsc::UnboundedReceiver<Event<A::Message>>,
    mut control_sender: mpsc::UnboundedSender<Control>,
    init_command: Command<A::Message>,
    mut window_manager: WindowManager<A, C>,
    should_main_window_be_visible: bool,
) where
    A: Application + 'static,
    E: Executor + 'static,
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: StyleSheet,
{
    use winit::event;
    use winit::event_loop::ControlFlow;

    let main_window = window_manager
        .get_mut(window::Id::MAIN)
        .expect("Get main window");

    if should_main_window_be_visible {
        main_window.raw.set_visible(true);
    }

    let mut clipboard = Clipboard::connect(&main_window.raw);
    let mut events = {
        vec![(
            Some(window::Id::MAIN),
            core::Event::Window(
                window::Id::MAIN,
                window::Event::Opened {
                    position: main_window.position(),
                    size: main_window.size(),
                },
            ),
        )]
    };

    let mut ui_caches = HashMap::new();
    let mut user_interfaces = ManuallyDrop::new(build_user_interfaces(
        &application,
        &mut debug,
        &mut window_manager,
        HashMap::from_iter([(
            window::Id::MAIN,
            user_interface::Cache::default(),
        )]),
    ));

    run_command(
        &application,
        &mut compositor,
        init_command,
        &mut runtime,
        &mut clipboard,
        &mut control_sender,
        &mut proxy,
        &mut debug,
        &mut window_manager,
        &mut ui_caches,
    );

    runtime.track(application.subscription().into_recipes());

    let mut messages = Vec::new();

    debug.startup_finished();

    'main: while let Some(event) = event_receiver.next().await {
        match event {
            Event::WindowCreated {
                id,
                window,
                exit_on_close_request,
            } => {
                let window = window_manager.insert(
                    id,
                    Arc::new(window),
                    &application,
                    &mut compositor,
                    exit_on_close_request,
                );

                let logical_size = window.state.logical_size();

                let _ = user_interfaces.insert(
                    id,
                    build_user_interface(
                        &application,
                        user_interface::Cache::default(),
                        &mut window.renderer,
                        logical_size,
                        &mut debug,
                        id,
                    ),
                );
                let _ = ui_caches.insert(id, user_interface::Cache::default());

                events.push((
                    Some(id),
                    core::Event::Window(
                        id,
                        window::Event::Opened {
                            position: window.position(),
                            size: window.size(),
                        },
                    ),
                ));
            }
            Event::EventLoopAwakened(event) => {
                match event {
                    event::Event::NewEvents(
                        event::StartCause::Init
                        | event::StartCause::ResumeTimeReached { .. },
                    ) => {
                        for (_id, window) in window_manager.iter_mut() {
                            // TODO once widgets can request to be redrawn, we can avoid always requesting a
                            // redraw
                            window.raw.request_redraw();
                        }
                    }
                    event::Event::PlatformSpecific(
                        event::PlatformSpecific::MacOS(
                            event::MacOS::ReceivedUrl(url),
                        ),
                    ) => {
                        use crate::core::event;

                        events.push((
                            None,
                            event::Event::PlatformSpecific(
                                event::PlatformSpecific::MacOS(
                                    event::MacOS::ReceivedUrl(url),
                                ),
                            ),
                        ));
                    }
                    event::Event::UserEvent(message) => {
                        messages.push(message);
                    }
                    event::Event::WindowEvent {
                        window_id: id,
                        event: event::WindowEvent::RedrawRequested,
                        ..
                    } => {
                        let Some((id, window)) =
                            window_manager.get_mut_alias(id)
                        else {
                            continue;
                        };

                        // TODO: Avoid redrawing all the time by forcing widgets to
                        // request redraws on state changes
                        //
                        // Then, we can use the `interface_state` here to decide if a redraw
                        // is needed right away, or simply wait until a specific time.
                        let redraw_event = core::Event::Window(
                            id,
                            window::Event::RedrawRequested(Instant::now()),
                        );

                        let cursor = window.state.cursor();

                        let ui = user_interfaces
                            .get_mut(&id)
                            .expect("Get user interface");

                        let (ui_state, _) = ui.update(
                            &[redraw_event.clone()],
                            cursor,
                            &mut window.renderer,
                            &mut clipboard,
                            &mut messages,
                        );

                        debug.draw_started();
                        let new_mouse_interaction = ui.draw(
                            &mut window.renderer,
                            window.state.theme(),
                            &renderer::Style {
                                text_color: window.state.text_color(),
                            },
                            cursor,
                        );
                        debug.draw_finished();

                        if new_mouse_interaction != window.mouse_interaction {
                            window.raw.set_cursor_icon(
                                conversion::mouse_interaction(
                                    new_mouse_interaction,
                                ),
                            );

                            window.mouse_interaction = new_mouse_interaction;
                        }

                        runtime.broadcast(
                            redraw_event.clone(),
                            core::event::Status::Ignored,
                        );

                        let _ = control_sender.start_send(Control::ChangeFlow(
                            match ui_state {
                                user_interface::State::Updated {
                                    redraw_request: Some(redraw_request),
                                } => match redraw_request {
                                    window::RedrawRequest::NextFrame => {
                                        window.raw.request_redraw();

                                        ControlFlow::Wait
                                    }
                                    window::RedrawRequest::At(at) => {
                                        ControlFlow::WaitUntil(at)
                                    }
                                },
                                _ => ControlFlow::Wait,
                            },
                        ));

                        let physical_size = window.state.physical_size();

                        if physical_size.width == 0 || physical_size.height == 0
                        {
                            continue;
                        }

                        if window.viewport_version
                            != window.state.viewport_version()
                        {
                            let logical_size = window.state.logical_size();

                            debug.layout_started();
                            let ui = user_interfaces
                                .remove(&id)
                                .expect("Remove user interface");

                            let _ = user_interfaces.insert(
                                id,
                                ui.relayout(logical_size, &mut window.renderer),
                            );
                            debug.layout_finished();

                            debug.draw_started();
                            let new_mouse_interaction = user_interfaces
                                .get_mut(&id)
                                .expect("Get user interface")
                                .draw(
                                    &mut window.renderer,
                                    window.state.theme(),
                                    &renderer::Style {
                                        text_color: window.state.text_color(),
                                    },
                                    window.state.cursor(),
                                );
                            debug.draw_finished();

                            if new_mouse_interaction != window.mouse_interaction
                            {
                                window.raw.set_cursor_icon(
                                    conversion::mouse_interaction(
                                        new_mouse_interaction,
                                    ),
                                );

                                window.mouse_interaction =
                                    new_mouse_interaction;
                            }

                            compositor.configure_surface(
                                &mut window.surface,
                                physical_size.width,
                                physical_size.height,
                            );

                            window.viewport_version =
                                window.state.viewport_version();
                        }

                        debug.render_started();
                        match compositor.present(
                            &mut window.renderer,
                            &mut window.surface,
                            window.state.viewport(),
                            window.state.background_color(),
                            &debug.overlay(),
                        ) {
                            Ok(()) => {
                                debug.render_finished();

                                // TODO: Handle animations!
                                // Maybe we can use `ControlFlow::WaitUntil` for this.
                            }
                            Err(error) => match error {
                                // This is an unrecoverable error.
                                compositor::SurfaceError::OutOfMemory => {
                                    panic!("{:?}", error);
                                }
                                _ => {
                                    debug.render_finished();

                                    log::error!(
                                        "Error {error:?} when \
                                        presenting surface."
                                    );

                                    // Try rendering all windows again next frame.
                                    for (_id, window) in
                                        window_manager.iter_mut()
                                    {
                                        window.raw.request_redraw();
                                    }
                                }
                            },
                        }
                    }
                    event::Event::WindowEvent {
                        event: window_event,
                        window_id,
                    } => {
                        let Some((id, window)) =
                            window_manager.get_mut_alias(window_id)
                        else {
                            continue;
                        };

                        if matches!(
                            window_event,
                            winit::event::WindowEvent::CloseRequested
                        ) && window.exit_on_close_request
                        {
                            let _ = window_manager.remove(id);
                            let _ = user_interfaces.remove(&id);
                            let _ = ui_caches.remove(&id);

                            events.push((
                                None,
                                core::Event::Window(id, window::Event::Closed),
                            ));

                            if window_manager.is_empty() {
                                break 'main;
                            }
                        } else {
                            window.state.update(
                                &window.raw,
                                &window_event,
                                &mut debug,
                            );

                            if let Some(event) = conversion::window_event(
                                id,
                                window_event,
                                window.state.scale_factor(),
                                window.state.modifiers(),
                            ) {
                                events.push((Some(id), event));
                            }
                        }
                    }
                    event::Event::AboutToWait => {
                        if events.is_empty() && messages.is_empty() {
                            continue;
                        }

                        debug.event_processing_started();
                        let mut uis_stale = false;

                        for (id, window) in window_manager.iter_mut() {
                            let mut window_events = vec![];

                            events.retain(|(window_id, event)| {
                                if *window_id == Some(id) || window_id.is_none()
                                {
                                    window_events.push(event.clone());
                                    false
                                } else {
                                    true
                                }
                            });

                            if window_events.is_empty() && messages.is_empty() {
                                continue;
                            }

                            let (ui_state, statuses) = user_interfaces
                                .get_mut(&id)
                                .expect("Get user interface")
                                .update(
                                    &window_events,
                                    window.state.cursor(),
                                    &mut window.renderer,
                                    &mut clipboard,
                                    &mut messages,
                                );

                            window.raw.request_redraw();

                            if !uis_stale {
                                uis_stale = matches!(
                                    ui_state,
                                    user_interface::State::Outdated
                                );
                            }

                            for (event, status) in window_events
                                .into_iter()
                                .zip(statuses.into_iter())
                            {
                                runtime.broadcast(event, status);
                            }
                        }

                        debug.event_processing_finished();

                        // TODO mw application update returns which window IDs to update
                        if !messages.is_empty() || uis_stale {
                            let mut cached_interfaces: HashMap<
                                window::Id,
                                user_interface::Cache,
                            > = ManuallyDrop::into_inner(user_interfaces)
                                .drain()
                                .map(|(id, ui)| (id, ui.into_cache()))
                                .collect();

                            // Update application
                            update(
                                &mut application,
                                &mut compositor,
                                &mut runtime,
                                &mut clipboard,
                                &mut control_sender,
                                &mut proxy,
                                &mut debug,
                                &mut messages,
                                &mut window_manager,
                                &mut cached_interfaces,
                            );

                            // we must synchronize all window states with application state after an
                            // application update since we don't know what changed
                            for (id, window) in window_manager.iter_mut() {
                                window.state.synchronize(
                                    &application,
                                    id,
                                    &window.raw,
                                );

                                // TODO once widgets can request to be redrawn, we can avoid always requesting a
                                // redraw
                                window.raw.request_redraw();
                            }

                            // rebuild UIs with the synchronized states
                            user_interfaces =
                                ManuallyDrop::new(build_user_interfaces(
                                    &application,
                                    &mut debug,
                                    &mut window_manager,
                                    cached_interfaces,
                                ));
                        }
                    }
                    _ => {}
                }
            }
        }
    }

    let _ = ManuallyDrop::into_inner(user_interfaces);
}

/// Builds a window's [`UserInterface`] for the [`Application`].
fn build_user_interface<'a, A: Application>(
    application: &'a A,
    cache: user_interface::Cache,
    renderer: &mut A::Renderer,
    size: Size,
    debug: &mut Debug,
    id: window::Id,
) -> UserInterface<'a, A::Message, A::Theme, A::Renderer>
where
    A::Theme: StyleSheet,
{
    debug.view_started();
    let view = application.view(id);
    debug.view_finished();

    debug.layout_started();
    let user_interface = UserInterface::build(view, size, cache, renderer);
    debug.layout_finished();

    user_interface
}

/// Updates a multi-window [`Application`] by feeding it messages, spawning any
/// resulting [`Command`], and tracking its [`Subscription`].
fn update<A: Application, C, E: Executor>(
    application: &mut A,
    compositor: &mut C,
    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
    clipboard: &mut Clipboard,
    control_sender: &mut mpsc::UnboundedSender<Control>,
    proxy: &mut winit::event_loop::EventLoopProxy<A::Message>,
    debug: &mut Debug,
    messages: &mut Vec<A::Message>,
    window_manager: &mut WindowManager<A, C>,
    ui_caches: &mut HashMap<window::Id, user_interface::Cache>,
) where
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: StyleSheet,
{
    for message in messages.drain(..) {
        debug.log_message(&message);
        debug.update_started();

        let command = runtime.enter(|| application.update(message));
        debug.update_finished();

        run_command(
            application,
            compositor,
            command,
            runtime,
            clipboard,
            control_sender,
            proxy,
            debug,
            window_manager,
            ui_caches,
        );
    }

    let subscription = application.subscription();
    runtime.track(subscription.into_recipes());
}

/// Runs the actions of a [`Command`].
fn run_command<A, C, E>(
    application: &A,
    compositor: &mut C,
    command: Command<A::Message>,
    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
    clipboard: &mut Clipboard,
    control_sender: &mut mpsc::UnboundedSender<Control>,
    proxy: &mut winit::event_loop::EventLoopProxy<A::Message>,
    debug: &mut Debug,
    window_manager: &mut WindowManager<A, C>,
    ui_caches: &mut HashMap<window::Id, user_interface::Cache>,
) where
    A: Application,
    E: Executor,
    C: Compositor<Renderer = A::Renderer> + 'static,
    A::Theme: StyleSheet,
{
    use crate::runtime::clipboard;
    use crate::runtime::system;
    use crate::runtime::window;

    for action in command.actions() {
        match action {
            command::Action::Future(future) => {
                runtime.spawn(Box::pin(future));
            }
            command::Action::Stream(stream) => {
                runtime.run(Box::pin(stream));
            }
            command::Action::Clipboard(action) => match action {
                clipboard::Action::Read(tag, kind) => {
                    let message = tag(clipboard.read(kind));

                    proxy
                        .send_event(message)
                        .expect("Send message to event loop");
                }
                clipboard::Action::Write(contents, kind) => {
                    clipboard.write(kind, contents);
                }
            },
            command::Action::Window(action) => match action {
                window::Action::Spawn(id, settings) => {
                    let monitor = window_manager.last_monitor();

                    control_sender
                        .start_send(Control::CreateWindow {
                            id,
                            settings,
                            title: application.title(id),
                            monitor,
                        })
                        .expect("Send control action");
                }
                window::Action::Close(id) => {
                    let _ = window_manager.remove(id);
                    let _ = ui_caches.remove(&id);

                    if window_manager.is_empty() {
                        control_sender
                            .start_send(Control::Exit)
                            .expect("Send control action");
                    }
                }
                window::Action::Drag(id) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        let _ = window.raw.drag_window();
                    }
                }
                window::Action::Resize(id, size) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        let _ = window.raw.request_inner_size(
                            winit::dpi::LogicalSize {
                                width: size.width,
                                height: size.height,
                            },
                        );
                    }
                }
                window::Action::FetchSize(id, callback) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        let size = window
                            .raw
                            .inner_size()
                            .to_logical(window.raw.scale_factor());

                        proxy
                            .send_event(callback(Size::new(
                                size.width,
                                size.height,
                            )))
                            .expect("Send message to event loop");
                    }
                }
                window::Action::FetchMaximized(id, callback) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        proxy
                            .send_event(callback(window.raw.is_maximized()))
                            .expect("Send message to event loop");
                    }
                }
                window::Action::Maximize(id, maximized) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_maximized(maximized);
                    }
                }
                window::Action::FetchMinimized(id, callback) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        proxy
                            .send_event(callback(window.raw.is_minimized()))
                            .expect("Send message to event loop");
                    }
                }
                window::Action::Minimize(id, minimized) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_minimized(minimized);
                    }
                }
                window::Action::Move(id, position) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_outer_position(
                            winit::dpi::LogicalPosition {
                                x: position.x,
                                y: position.y,
                            },
                        );
                    }
                }
                window::Action::ChangeMode(id, mode) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_visible(conversion::visible(mode));
                        window.raw.set_fullscreen(conversion::fullscreen(
                            window.raw.current_monitor(),
                            mode,
                        ));
                    }
                }
                window::Action::ChangeIcon(id, icon) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_window_icon(conversion::icon(icon));
                    }
                }
                window::Action::FetchMode(id, tag) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        let mode = if window.raw.is_visible().unwrap_or(true) {
                            conversion::mode(window.raw.fullscreen())
                        } else {
                            core::window::Mode::Hidden
                        };

                        proxy
                            .send_event(tag(mode))
                            .expect("Send message to event loop");
                    }
                }
                window::Action::ToggleMaximize(id) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_maximized(!window.raw.is_maximized());
                    }
                }
                window::Action::ToggleDecorations(id) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.set_decorations(!window.raw.is_decorated());
                    }
                }
                window::Action::RequestUserAttention(id, attention_type) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.request_user_attention(
                            attention_type.map(conversion::user_attention),
                        );
                    }
                }
                window::Action::GainFocus(id) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window.raw.focus_window();
                    }
                }
                window::Action::ChangeLevel(id, level) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        window
                            .raw
                            .set_window_level(conversion::window_level(level));
                    }
                }
                window::Action::ShowSystemMenu(id) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        if let mouse::Cursor::Available(point) =
                            window.state.cursor()
                        {
                            window.raw.show_window_menu(
                                winit::dpi::LogicalPosition {
                                    x: point.x,
                                    y: point.y,
                                },
                            );
                        }
                    }
                }
                window::Action::FetchId(id, tag) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        proxy
                            .send_event(tag(window.raw.id().into()))
                            .expect("Send message to event loop");
                    }
                }
                window::Action::RunWithHandle(id, tag) => {
                    use window::raw_window_handle::HasWindowHandle;

                    if let Some(handle) = window_manager
                        .get_mut(id)
                        .and_then(|window| window.raw.window_handle().ok())
                    {
                        proxy
                            .send_event(tag(&handle))
                            .expect("Send message to event loop");
                    }
                }
                window::Action::Screenshot(id, tag) => {
                    if let Some(window) = window_manager.get_mut(id) {
                        let bytes = compositor.screenshot(
                            &mut window.renderer,
                            &mut window.surface,
                            window.state.viewport(),
                            window.state.background_color(),
                            &debug.overlay(),
                        );

                        proxy
                            .send_event(tag(window::Screenshot::new(
                                bytes,
                                window.state.physical_size(),
                            )))
                            .expect("Event loop doesn't exist.");
                    }
                }
            },
            command::Action::System(action) => match action {
                system::Action::QueryInformation(_tag) => {
                    #[cfg(feature = "system")]
                    {
                        let graphics_info = compositor.fetch_information();
                        let proxy = proxy.clone();

                        let _ = std::thread::spawn(move || {
                            let information =
                                crate::system::information(graphics_info);

                            let message = _tag(information);

                            proxy
                                .send_event(message)
                                .expect("Event loop doesn't exist.");
                        });
                    }
                }
            },
            command::Action::Widget(action) => {
                let mut current_operation = Some(action);

                let mut uis = build_user_interfaces(
                    application,
                    debug,
                    window_manager,
                    std::mem::take(ui_caches),
                );

                'operate: while let Some(mut operation) =
                    current_operation.take()
                {
                    for (id, ui) in uis.iter_mut() {
                        if let Some(window) = window_manager.get_mut(*id) {
                            ui.operate(&window.renderer, operation.as_mut());

                            match operation.finish() {
                                operation::Outcome::None => {}
                                operation::Outcome::Some(message) => {
                                    proxy
                                        .send_event(message)
                                        .expect("Event loop doesn't exist.");

                                    // operation completed, don't need to try to operate on rest of UIs
                                    break 'operate;
                                }
                                operation::Outcome::Chain(next) => {
                                    current_operation = Some(next);
                                }
                            }
                        }
                    }
                }

                *ui_caches =
                    uis.drain().map(|(id, ui)| (id, ui.into_cache())).collect();
            }
            command::Action::LoadFont { bytes, tagger } => {
                use crate::core::text::Renderer;

                // TODO change this once we change each renderer to having a single backend reference.. :pain:
                // TODO: Error handling (?)
                for (_, window) in window_manager.iter_mut() {
                    window.renderer.load_font(bytes.clone());
                }

                proxy
                    .send_event(tagger(Ok(())))
                    .expect("Send message to event loop");
            }
            command::Action::Custom(_) => {
                log::warn!("Unsupported custom action in `iced_winit` shell");
            }
        }
    }
}

/// Build the user interface for every window.
pub fn build_user_interfaces<'a, A: Application, C: Compositor>(
    application: &'a A,
    debug: &mut Debug,
    window_manager: &mut WindowManager<A, C>,
    mut cached_user_interfaces: HashMap<window::Id, user_interface::Cache>,
) -> HashMap<window::Id, UserInterface<'a, A::Message, A::Theme, A::Renderer>>
where
    A::Theme: StyleSheet,
    C: Compositor<Renderer = A::Renderer>,
{
    cached_user_interfaces
        .drain()
        .filter_map(|(id, cache)| {
            let window = window_manager.get_mut(id)?;

            Some((
                id,
                build_user_interface(
                    application,
                    cache,
                    &mut window.renderer,
                    window.state.logical_size(),
                    debug,
                    id,
                ),
            ))
        })
        .collect()
}

/// Returns true if the provided event should cause an [`Application`] to
/// exit.
pub fn user_force_quit(
    event: &winit::event::WindowEvent,
    _modifiers: winit::keyboard::ModifiersState,
) -> bool {
    match event {
        #[cfg(target_os = "macos")]
        winit::event::WindowEvent::KeyboardInput {
            event:
                winit::event::KeyEvent {
                    logical_key: winit::keyboard::Key::Character(c),
                    state: winit::event::ElementState::Pressed,
                    ..
                },
            ..
        } if c == "q" && _modifiers.super_key() => true,
        _ => false,
    }
}