#![deny(unused_results)]

use std::cell::{OnceCell, RefCell, RefMut};
use std::collections::HashSet;
use std::os::raw::c_void;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex, OnceLock};
use std::time::Instant;
use std::{mem, ptr};

use core_foundation::base::CFRelease;
use core_foundation::date::CFAbsoluteTimeGetCurrent;
use core_foundation::runloop::{
    kCFRunLoopCommonModes, CFRunLoopAddTimer, CFRunLoopGetMain, CFRunLoopRef, CFRunLoopTimerCreate,
    CFRunLoopTimerInvalidate, CFRunLoopTimerRef, CFRunLoopTimerSetNextFireDate,
};
use objc2::rc::Retained;
use objc2::sel;
use objc2_foundation::{
    CGRect, CGSize, MainThreadMarker, NSInteger, NSObjectProtocol, NSOperatingSystemVersion,
    NSProcessInfo,
};
use objc2_ui_kit::{UIApplication, UICoordinateSpace, UIView, UIWindow};

use super::super::event_handler::EventHandler;
use super::window::WinitUIWindow;
use super::ActiveEventLoop;
use crate::application::ApplicationHandler;
use crate::dpi::PhysicalSize;
use crate::event::{Event, StartCause, SurfaceSizeWriter, WindowEvent};
use crate::event_loop::ControlFlow;
use crate::window::WindowId as RootWindowId;

macro_rules! bug {
    ($($msg:tt)*) => {
        panic!("winit iOS bug, file an issue: {}", format!($($msg)*))
    };
}

macro_rules! bug_assert {
    ($test:expr, $($msg:tt)*) => {
        assert!($test, "winit iOS bug, file an issue: {}", format!($($msg)*))
    };
}

/// Get the global event handler for the application.
///
/// This is stored separately from AppState, since AppState needs to be accessible while the handler
/// is executing.
fn get_handler(mtm: MainThreadMarker) -> &'static EventHandler {
    // TODO(madsmtm): Use `MainThreadBound` once that is possible in `static`s.
    struct StaticMainThreadBound<T>(T);

    impl<T> StaticMainThreadBound<T> {
        const fn get(&self, _mtm: MainThreadMarker) -> &T {
            &self.0
        }
    }

    unsafe impl<T> Send for StaticMainThreadBound<T> {}
    unsafe impl<T> Sync for StaticMainThreadBound<T> {}

    // SAFETY: Creating `StaticMainThreadBound` in a `const` context, where there is no concept
    // of the main thread.
    static GLOBAL: StaticMainThreadBound<OnceCell<EventHandler>> =
        StaticMainThreadBound(OnceCell::new());

    GLOBAL.get(mtm).get_or_init(EventHandler::new)
}

fn handle_event(mtm: MainThreadMarker, event: Event) {
    let event_loop = &ActiveEventLoop { mtm };
    get_handler(mtm).handle(|app| match event {
        Event::NewEvents(cause) => app.new_events(event_loop, cause),
        Event::WindowEvent { window_id, event } => app.window_event(event_loop, window_id, event),
        Event::DeviceEvent { device_id, event } => app.device_event(event_loop, device_id, event),
        Event::UserWakeUp => app.proxy_wake_up(event_loop),
        Event::Suspended => app.suspended(event_loop),
        Event::Resumed => app.resumed(event_loop),
        Event::CreateSurfaces => app.can_create_surfaces(event_loop),
        Event::AboutToWait => app.about_to_wait(event_loop),
        Event::LoopExiting => app.exiting(event_loop),
        Event::MemoryWarning => app.memory_warning(event_loop),
    })
}

#[derive(Debug)]
pub(crate) enum EventWrapper {
    StaticEvent(Event),
    ScaleFactorChanged(ScaleFactorChanged),
}

#[derive(Debug)]
pub struct ScaleFactorChanged {
    pub(super) window: Retained<WinitUIWindow>,
    pub(super) suggested_size: PhysicalSize<u32>,
    pub(super) scale_factor: f64,
}

enum UserCallbackTransitionResult<'a> {
    Success { active_control_flow: ControlFlow, processing_redraws: bool },
    ReentrancyPrevented { queued_events: &'a mut Vec<EventWrapper> },
}

impl Event {
    fn is_redraw(&self) -> bool {
        matches!(self, Event::WindowEvent { event: WindowEvent::RedrawRequested, .. })
    }
}

// this is the state machine for the app lifecycle
#[derive(Debug)]
#[must_use = "dropping `AppStateImpl` without inspecting it is probably a bug"]
enum AppStateImpl {
    Initial {
        queued_events: Vec<EventWrapper>,
        queued_gpu_redraws: HashSet<Retained<WinitUIWindow>>,
    },
    ProcessingEvents {
        queued_gpu_redraws: HashSet<Retained<WinitUIWindow>>,
        active_control_flow: ControlFlow,
    },
    // special state to deal with reentrancy and prevent mutable aliasing.
    InUserCallback {
        queued_events: Vec<EventWrapper>,
        queued_gpu_redraws: HashSet<Retained<WinitUIWindow>>,
    },
    ProcessingRedraws {
        active_control_flow: ControlFlow,
    },
    Waiting {
        start: Instant,
    },
    PollFinished,
    Terminated,
}

pub(crate) struct AppState {
    // This should never be `None`, except for briefly during a state transition.
    app_state: Option<AppStateImpl>,
    control_flow: ControlFlow,
    waker: EventLoopWaker,
    proxy_wake_up: Arc<AtomicBool>,
}

impl AppState {
    pub(crate) fn get_mut(_mtm: MainThreadMarker) -> RefMut<'static, AppState> {
        // basically everything in UIKit requires the main thread, so it's pointless to use the
        // std::sync APIs.
        // must be mut because plain `static` requires `Sync`
        static mut APP_STATE: RefCell<Option<AppState>> = RefCell::new(None);

        #[allow(unknown_lints)] // New lint below
        #[allow(static_mut_refs)] // TODO: Use `MainThreadBound` instead.
        let mut guard = unsafe { APP_STATE.borrow_mut() };
        if guard.is_none() {
            #[inline(never)]
            #[cold]
            fn init_guard(guard: &mut RefMut<'static, Option<AppState>>) {
                let waker = EventLoopWaker::new(unsafe { CFRunLoopGetMain() });
                **guard = Some(AppState {
                    app_state: Some(AppStateImpl::Initial {
                        queued_events: Vec::new(),
                        queued_gpu_redraws: HashSet::new(),
                    }),
                    control_flow: ControlFlow::default(),
                    waker,
                    proxy_wake_up: Arc::new(AtomicBool::new(false)),
                });
            }
            init_guard(&mut guard);
        }
        RefMut::map(guard, |state| state.as_mut().unwrap())
    }

    fn state(&self) -> &AppStateImpl {
        match &self.app_state {
            Some(ref state) => state,
            None => bug!("`AppState` previously failed a state transition"),
        }
    }

    fn state_mut(&mut self) -> &mut AppStateImpl {
        match &mut self.app_state {
            Some(ref mut state) => state,
            None => bug!("`AppState` previously failed a state transition"),
        }
    }

    fn take_state(&mut self) -> AppStateImpl {
        match self.app_state.take() {
            Some(state) => state,
            None => bug!("`AppState` previously failed a state transition"),
        }
    }

    fn set_state(&mut self, new_state: AppStateImpl) {
        bug_assert!(
            self.app_state.is_none(),
            "attempted to set an `AppState` without calling `take_state` first {:?}",
            self.app_state
        );
        self.app_state = Some(new_state)
    }

    fn replace_state(&mut self, new_state: AppStateImpl) -> AppStateImpl {
        match &mut self.app_state {
            Some(ref mut state) => mem::replace(state, new_state),
            None => bug!("`AppState` previously failed a state transition"),
        }
    }

    fn has_launched(&self) -> bool {
        !matches!(self.state(), AppStateImpl::Initial { .. })
    }

    fn has_terminated(&self) -> bool {
        matches!(self.state(), AppStateImpl::Terminated)
    }

    fn did_finish_launching_transition(&mut self) -> Vec<EventWrapper> {
        let (events, queued_gpu_redraws) = match self.take_state() {
            AppStateImpl::Initial { queued_events, queued_gpu_redraws } => {
                (queued_events, queued_gpu_redraws)
            },
            s => bug!("unexpected state {:?}", s),
        };
        self.set_state(AppStateImpl::ProcessingEvents {
            active_control_flow: self.control_flow,
            queued_gpu_redraws,
        });
        events
    }

    fn wakeup_transition(&mut self) -> Option<EventWrapper> {
        // before `AppState::did_finish_launching` is called, pretend there is no running
        // event loop.
        if !self.has_launched() || self.has_terminated() {
            return None;
        }

        let event = match (self.control_flow, self.take_state()) {
            (ControlFlow::Poll, AppStateImpl::PollFinished) => {
                EventWrapper::StaticEvent(Event::NewEvents(StartCause::Poll))
            },
            (ControlFlow::Wait, AppStateImpl::Waiting { start }) => {
                EventWrapper::StaticEvent(Event::NewEvents(StartCause::WaitCancelled {
                    start,
                    requested_resume: None,
                }))
            },
            (ControlFlow::WaitUntil(requested_resume), AppStateImpl::Waiting { start }) => {
                if Instant::now() >= requested_resume {
                    EventWrapper::StaticEvent(Event::NewEvents(StartCause::ResumeTimeReached {
                        start,
                        requested_resume,
                    }))
                } else {
                    EventWrapper::StaticEvent(Event::NewEvents(StartCause::WaitCancelled {
                        start,
                        requested_resume: Some(requested_resume),
                    }))
                }
            },
            s => bug!("`EventHandler` unexpectedly woke up {:?}", s),
        };

        self.set_state(AppStateImpl::ProcessingEvents {
            queued_gpu_redraws: Default::default(),
            active_control_flow: self.control_flow,
        });
        Some(event)
    }

    fn try_user_callback_transition(&mut self) -> UserCallbackTransitionResult<'_> {
        // If we're not able to process an event due to recursion or `Init` not having been sent out
        // yet, then queue the events up.
        match self.state_mut() {
            &mut AppStateImpl::Initial { ref mut queued_events, .. }
            | &mut AppStateImpl::InUserCallback { ref mut queued_events, .. } => {
                // A lifetime cast: early returns are not currently handled well with NLL, but
                // polonius handles them well. This transmute is a safe workaround.
                return unsafe {
                    mem::transmute::<
                        UserCallbackTransitionResult<'_>,
                        UserCallbackTransitionResult<'_>,
                    >(UserCallbackTransitionResult::ReentrancyPrevented {
                        queued_events,
                    })
                };
            },

            &mut AppStateImpl::ProcessingEvents { .. }
            | &mut AppStateImpl::ProcessingRedraws { .. } => {},

            s @ &mut AppStateImpl::PollFinished { .. }
            | s @ &mut AppStateImpl::Waiting { .. }
            | s @ &mut AppStateImpl::Terminated => {
                bug!("unexpected attempted to process an event {:?}", s)
            },
        }

        let (queued_gpu_redraws, active_control_flow, processing_redraws) = match self.take_state()
        {
            AppStateImpl::Initial { .. } | AppStateImpl::InUserCallback { .. } => unreachable!(),
            AppStateImpl::ProcessingEvents { queued_gpu_redraws, active_control_flow } => {
                (queued_gpu_redraws, active_control_flow, false)
            },
            AppStateImpl::ProcessingRedraws { active_control_flow } => {
                (Default::default(), active_control_flow, true)
            },
            AppStateImpl::PollFinished { .. }
            | AppStateImpl::Waiting { .. }
            | AppStateImpl::Terminated => unreachable!(),
        };
        self.set_state(AppStateImpl::InUserCallback {
            queued_events: Vec::new(),
            queued_gpu_redraws,
        });
        UserCallbackTransitionResult::Success { active_control_flow, processing_redraws }
    }

    fn main_events_cleared_transition(&mut self) -> HashSet<Retained<WinitUIWindow>> {
        let (queued_gpu_redraws, active_control_flow) = match self.take_state() {
            AppStateImpl::ProcessingEvents { queued_gpu_redraws, active_control_flow } => {
                (queued_gpu_redraws, active_control_flow)
            },
            s => bug!("unexpected state {:?}", s),
        };
        self.set_state(AppStateImpl::ProcessingRedraws { active_control_flow });
        queued_gpu_redraws
    }

    fn events_cleared_transition(&mut self) {
        if !self.has_launched() || self.has_terminated() {
            return;
        }
        let old = match self.take_state() {
            AppStateImpl::ProcessingRedraws { active_control_flow } => active_control_flow,
            s => bug!("unexpected state {:?}", s),
        };

        let new = self.control_flow;
        match (old, new) {
            (ControlFlow::Wait, ControlFlow::Wait) => {
                let start = Instant::now();
                self.set_state(AppStateImpl::Waiting { start });
            },
            (ControlFlow::WaitUntil(old_instant), ControlFlow::WaitUntil(new_instant))
                if old_instant == new_instant =>
            {
                let start = Instant::now();
                self.set_state(AppStateImpl::Waiting { start });
            },
            (_, ControlFlow::Wait) => {
                let start = Instant::now();
                self.set_state(AppStateImpl::Waiting { start });
                self.waker.stop()
            },
            (_, ControlFlow::WaitUntil(new_instant)) => {
                let start = Instant::now();
                self.set_state(AppStateImpl::Waiting { start });
                self.waker.start_at(new_instant)
            },
            // Unlike on macOS, handle Poll to Poll transition here to call the waker
            (_, ControlFlow::Poll) => {
                self.set_state(AppStateImpl::PollFinished);
                self.waker.start()
            },
        }
    }

    fn terminated_transition(&mut self) {
        match self.replace_state(AppStateImpl::Terminated) {
            AppStateImpl::ProcessingEvents { .. } => {},
            s => bug!("`LoopExiting` happened while not processing events {:?}", s),
        }
    }

    pub(crate) fn proxy_wake_up(&self) -> Arc<AtomicBool> {
        self.proxy_wake_up.clone()
    }

    pub(crate) fn set_control_flow(&mut self, control_flow: ControlFlow) {
        self.control_flow = control_flow;
    }

    pub(crate) fn control_flow(&self) -> ControlFlow {
        self.control_flow
    }
}

pub(crate) fn queue_gl_or_metal_redraw(mtm: MainThreadMarker, window: Retained<WinitUIWindow>) {
    let mut this = AppState::get_mut(mtm);
    match this.state_mut() {
        &mut AppStateImpl::Initial { ref mut queued_gpu_redraws, .. }
        | &mut AppStateImpl::ProcessingEvents { ref mut queued_gpu_redraws, .. }
        | &mut AppStateImpl::InUserCallback { ref mut queued_gpu_redraws, .. } => {
            let _ = queued_gpu_redraws.insert(window);
        },
        s @ &mut AppStateImpl::ProcessingRedraws { .. }
        | s @ &mut AppStateImpl::Waiting { .. }
        | s @ &mut AppStateImpl::PollFinished { .. } => bug!("unexpected state {:?}", s),
        &mut AppStateImpl::Terminated => {
            panic!("Attempt to create a `Window` after the app has terminated")
        },
    }
}

pub(crate) fn launch(mtm: MainThreadMarker, app: &mut dyn ApplicationHandler, run: impl FnOnce()) {
    get_handler(mtm).set(app, run)
}

pub fn did_finish_launching(mtm: MainThreadMarker) {
    let mut this = AppState::get_mut(mtm);

    this.waker.start();

    // have to drop RefMut because the window setup code below can trigger new events
    drop(this);

    let events = AppState::get_mut(mtm).did_finish_launching_transition();

    let events = [
        EventWrapper::StaticEvent(Event::NewEvents(StartCause::Init)),
        EventWrapper::StaticEvent(Event::CreateSurfaces),
    ]
    .into_iter()
    .chain(events);
    handle_nonuser_events(mtm, events);
}

// AppState::did_finish_launching handles the special transition `Init`
pub fn handle_wakeup_transition(mtm: MainThreadMarker) {
    let mut this = AppState::get_mut(mtm);
    let wakeup_event = match this.wakeup_transition() {
        None => return,
        Some(wakeup_event) => wakeup_event,
    };
    drop(this);

    handle_nonuser_event(mtm, wakeup_event)
}

pub(crate) fn handle_nonuser_event(mtm: MainThreadMarker, event: EventWrapper) {
    handle_nonuser_events(mtm, std::iter::once(event))
}

pub(crate) fn handle_nonuser_events<I: IntoIterator<Item = EventWrapper>>(
    mtm: MainThreadMarker,
    events: I,
) {
    let mut this = AppState::get_mut(mtm);
    if this.has_terminated() {
        return;
    }

    let (active_control_flow, processing_redraws) = match this.try_user_callback_transition() {
        UserCallbackTransitionResult::ReentrancyPrevented { queued_events } => {
            queued_events.extend(events);
            return;
        },
        UserCallbackTransitionResult::Success { active_control_flow, processing_redraws } => {
            (active_control_flow, processing_redraws)
        },
    };
    drop(this);

    for wrapper in events {
        match wrapper {
            EventWrapper::StaticEvent(event) => {
                if !processing_redraws && event.is_redraw() {
                    tracing::info!("processing `RedrawRequested` during the main event loop");
                } else if processing_redraws && !event.is_redraw() {
                    tracing::warn!(
                        "processing non `RedrawRequested` event after the main event loop: {:#?}",
                        event
                    );
                }
                handle_event(mtm, event)
            },
            EventWrapper::ScaleFactorChanged(event) => handle_hidpi_proxy(mtm, event),
        }
    }

    loop {
        let mut this = AppState::get_mut(mtm);
        let queued_events = match this.state_mut() {
            &mut AppStateImpl::InUserCallback { ref mut queued_events, queued_gpu_redraws: _ } => {
                mem::take(queued_events)
            },
            s => bug!("unexpected state {:?}", s),
        };
        if queued_events.is_empty() {
            let queued_gpu_redraws = match this.take_state() {
                AppStateImpl::InUserCallback { queued_events: _, queued_gpu_redraws } => {
                    queued_gpu_redraws
                },
                _ => unreachable!(),
            };
            this.app_state = Some(if processing_redraws {
                bug_assert!(
                    queued_gpu_redraws.is_empty(),
                    "redraw queued while processing redraws"
                );
                AppStateImpl::ProcessingRedraws { active_control_flow }
            } else {
                AppStateImpl::ProcessingEvents { queued_gpu_redraws, active_control_flow }
            });
            break;
        }
        drop(this);

        for wrapper in queued_events {
            match wrapper {
                EventWrapper::StaticEvent(event) => {
                    if !processing_redraws && event.is_redraw() {
                        tracing::info!("processing `RedrawRequested` during the main event loop");
                    } else if processing_redraws && !event.is_redraw() {
                        tracing::warn!(
                            "processing non-`RedrawRequested` event after the main event loop: \
                             {:#?}",
                            event
                        );
                    }
                    handle_event(mtm, event)
                },
                EventWrapper::ScaleFactorChanged(event) => handle_hidpi_proxy(mtm, event),
            }
        }
    }
}

fn handle_user_events(mtm: MainThreadMarker) {
    let mut this = AppState::get_mut(mtm);
    let (active_control_flow, processing_redraws) = match this.try_user_callback_transition() {
        UserCallbackTransitionResult::ReentrancyPrevented { .. } => {
            bug!("unexpected attempted to process an event")
        },
        UserCallbackTransitionResult::Success { active_control_flow, processing_redraws } => {
            (active_control_flow, processing_redraws)
        },
    };
    if processing_redraws {
        bug!("user events attempted to be sent out while `ProcessingRedraws`");
    }
    let proxy_wake_up = this.proxy_wake_up.clone();
    drop(this);

    if proxy_wake_up.swap(false, Ordering::Relaxed) {
        handle_event(mtm, Event::UserWakeUp);
    }

    loop {
        let mut this = AppState::get_mut(mtm);
        let queued_events = match this.state_mut() {
            &mut AppStateImpl::InUserCallback { ref mut queued_events, queued_gpu_redraws: _ } => {
                mem::take(queued_events)
            },
            s => bug!("unexpected state {:?}", s),
        };
        if queued_events.is_empty() {
            let queued_gpu_redraws = match this.take_state() {
                AppStateImpl::InUserCallback { queued_events: _, queued_gpu_redraws } => {
                    queued_gpu_redraws
                },
                _ => unreachable!(),
            };
            this.app_state =
                Some(AppStateImpl::ProcessingEvents { queued_gpu_redraws, active_control_flow });
            break;
        }
        drop(this);

        for wrapper in queued_events {
            match wrapper {
                EventWrapper::StaticEvent(event) => handle_event(mtm, event),
                EventWrapper::ScaleFactorChanged(event) => handle_hidpi_proxy(mtm, event),
            }
        }

        if proxy_wake_up.swap(false, Ordering::Relaxed) {
            handle_event(mtm, Event::UserWakeUp);
        }
    }
}

pub(crate) fn send_occluded_event_for_all_windows(application: &UIApplication, occluded: bool) {
    let mtm = MainThreadMarker::from(application);

    let mut events = Vec::new();
    #[allow(deprecated)]
    for window in application.windows().iter() {
        if window.is_kind_of::<WinitUIWindow>() {
            // SAFETY: We just checked that the window is a `winit` window
            let window = unsafe {
                let ptr: *const UIWindow = window;
                let ptr: *const WinitUIWindow = ptr.cast();
                &*ptr
            };
            events.push(EventWrapper::StaticEvent(Event::WindowEvent {
                window_id: RootWindowId(window.id()),
                event: WindowEvent::Occluded(occluded),
            }));
        }
    }
    handle_nonuser_events(mtm, events);
}

pub fn handle_main_events_cleared(mtm: MainThreadMarker) {
    let mut this = AppState::get_mut(mtm);
    if !this.has_launched() || this.has_terminated() {
        return;
    }
    match this.state_mut() {
        AppStateImpl::ProcessingEvents { .. } => {},
        _ => bug!("`ProcessingRedraws` happened unexpectedly"),
    };
    drop(this);

    handle_user_events(mtm);

    let mut this = AppState::get_mut(mtm);
    let redraw_events: Vec<EventWrapper> = this
        .main_events_cleared_transition()
        .into_iter()
        .map(|window| {
            EventWrapper::StaticEvent(Event::WindowEvent {
                window_id: RootWindowId(window.id()),
                event: WindowEvent::RedrawRequested,
            })
        })
        .collect();
    drop(this);

    handle_nonuser_events(mtm, redraw_events);
    handle_nonuser_event(mtm, EventWrapper::StaticEvent(Event::AboutToWait));
}

pub fn handle_events_cleared(mtm: MainThreadMarker) {
    AppState::get_mut(mtm).events_cleared_transition();
}

pub(crate) fn terminated(application: &UIApplication) {
    let mtm = MainThreadMarker::from(application);

    let mut events = Vec::new();
    #[allow(deprecated)]
    for window in application.windows().iter() {
        if window.is_kind_of::<WinitUIWindow>() {
            // SAFETY: We just checked that the window is a `winit` window
            let window = unsafe {
                let ptr: *const UIWindow = window;
                let ptr: *const WinitUIWindow = ptr.cast();
                &*ptr
            };
            events.push(EventWrapper::StaticEvent(Event::WindowEvent {
                window_id: RootWindowId(window.id()),
                event: WindowEvent::Destroyed,
            }));
        }
    }
    handle_nonuser_events(mtm, events);

    let mut this = AppState::get_mut(mtm);
    this.terminated_transition();
    drop(this);

    handle_event(mtm, Event::LoopExiting)
}

fn handle_hidpi_proxy(mtm: MainThreadMarker, event: ScaleFactorChanged) {
    let ScaleFactorChanged { suggested_size, scale_factor, window } = event;
    let new_surface_size = Arc::new(Mutex::new(suggested_size));
    let event = Event::WindowEvent {
        window_id: RootWindowId(window.id()),
        event: WindowEvent::ScaleFactorChanged {
            scale_factor,
            surface_size_writer: SurfaceSizeWriter::new(Arc::downgrade(&new_surface_size)),
        },
    };
    handle_event(mtm, event);
    let (view, screen_frame) = get_view_and_screen_frame(&window);
    let physical_size = *new_surface_size.lock().unwrap();
    drop(new_surface_size);
    let logical_size = physical_size.to_logical(scale_factor);
    let size = CGSize::new(logical_size.width, logical_size.height);
    let new_frame: CGRect = CGRect::new(screen_frame.origin, size);
    view.setFrame(new_frame);
}

fn get_view_and_screen_frame(window: &WinitUIWindow) -> (Retained<UIView>, CGRect) {
    let view_controller = window.rootViewController().unwrap();
    let view = view_controller.view().unwrap();
    let bounds = window.bounds();
    let screen = window.screen();
    let screen_space = screen.coordinateSpace();
    let screen_frame = window.convertRect_toCoordinateSpace(bounds, &screen_space);
    (view, screen_frame)
}

struct EventLoopWaker {
    timer: CFRunLoopTimerRef,
}

impl Drop for EventLoopWaker {
    fn drop(&mut self) {
        unsafe {
            CFRunLoopTimerInvalidate(self.timer);
            CFRelease(self.timer as _);
        }
    }
}

impl EventLoopWaker {
    fn new(rl: CFRunLoopRef) -> EventLoopWaker {
        extern "C" fn wakeup_main_loop(_timer: CFRunLoopTimerRef, _info: *mut c_void) {}
        unsafe {
            // Create a timer with a 0.1µs interval (1ns does not work) to mimic polling.
            // It is initially setup with a first fire time really far into the
            // future, but that gets changed to fire immediately in did_finish_launching
            let timer = CFRunLoopTimerCreate(
                ptr::null_mut(),
                f64::MAX,
                0.000_000_1,
                0,
                0,
                wakeup_main_loop,
                ptr::null_mut(),
            );
            CFRunLoopAddTimer(rl, timer, kCFRunLoopCommonModes);

            EventLoopWaker { timer }
        }
    }

    fn stop(&mut self) {
        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MAX) }
    }

    fn start(&mut self) {
        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MIN) }
    }

    fn start_at(&mut self, instant: Instant) {
        let now = Instant::now();
        if now >= instant {
            self.start();
        } else {
            unsafe {
                let current = CFAbsoluteTimeGetCurrent();
                let duration = instant - now;
                let fsecs =
                    duration.subsec_nanos() as f64 / 1_000_000_000.0 + duration.as_secs() as f64;
                CFRunLoopTimerSetNextFireDate(self.timer, current + fsecs)
            }
        }
    }
}

macro_rules! os_capabilities {
    (
        $(
            $(#[$attr:meta])*
            $error_name:ident: $objc_call:literal,
            $name:ident: $major:literal-$minor:literal
        ),*
        $(,)*
    ) => {
        #[derive(Clone, Debug)]
        pub struct OSCapabilities {
            $(
                pub $name: bool,
            )*

            os_version: NSOperatingSystemVersion,
        }

        impl OSCapabilities {
            fn from_os_version(os_version: NSOperatingSystemVersion) -> Self {
                $(let $name = meets_requirements(os_version, $major, $minor);)*
                Self { $($name,)* os_version, }
            }
        }

        impl OSCapabilities {$(
            $(#[$attr])*
            pub fn $error_name(&self, extra_msg: &str) {
                tracing::warn!(
                    concat!("`", $objc_call, "` requires iOS {}.{}+. This device is running iOS {}.{}.{}. {}"),
                    $major, $minor, self.os_version.majorVersion, self.os_version.minorVersion, self.os_version.patchVersion,
                    extra_msg
                )
            }
        )*}
    };
}

os_capabilities! {
    /// <https://developer.apple.com/documentation/uikit/uiview/2891103-safeareainsets?language=objc>
    #[allow(unused)] // error message unused
    safe_area_err_msg: "-[UIView safeAreaInsets]",
    safe_area: 11-0,
    /// <https://developer.apple.com/documentation/uikit/uiviewcontroller/2887509-setneedsupdateofhomeindicatoraut?language=objc>
    home_indicator_hidden_err_msg: "-[UIViewController setNeedsUpdateOfHomeIndicatorAutoHidden]",
    home_indicator_hidden: 11-0,
    /// <https://developer.apple.com/documentation/uikit/uiviewcontroller/2887507-setneedsupdateofscreenedgesdefer?language=objc>
    defer_system_gestures_err_msg: "-[UIViewController setNeedsUpdateOfScreenEdgesDeferringSystem]",
    defer_system_gestures: 11-0,
    /// <https://developer.apple.com/documentation/uikit/uiscreen/2806814-maximumframespersecond?language=objc>
    maximum_frames_per_second_err_msg: "-[UIScreen maximumFramesPerSecond]",
    maximum_frames_per_second: 10-3,
    /// <https://developer.apple.com/documentation/uikit/uitouch/1618110-force?language=objc>
    #[allow(unused)] // error message unused
    force_touch_err_msg: "-[UITouch force]",
    force_touch: 9-0,
}

fn meets_requirements(
    version: NSOperatingSystemVersion,
    required_major: NSInteger,
    required_minor: NSInteger,
) -> bool {
    (version.majorVersion, version.minorVersion) >= (required_major, required_minor)
}

fn get_version() -> NSOperatingSystemVersion {
    let process_info = NSProcessInfo::processInfo();
    let atleast_ios_8 = process_info.respondsToSelector(sel!(operatingSystemVersion));
    // Winit requires atleast iOS 8 because no one has put the time into supporting earlier os
    // versions. Older iOS versions are increasingly difficult to test. For example, Xcode 11 does
    // not support debugging on devices with an iOS version of less than 8. Another example, in
    // order to use an iOS simulator older than iOS 8, you must download an older version of Xcode
    // (<9), and at least Xcode 7 has been tested to not even run on macOS 10.15 - Xcode 8 might?
    //
    // The minimum required iOS version is likely to grow in the future.
    assert!(atleast_ios_8, "`winit` requires iOS version 8 or greater");
    process_info.operatingSystemVersion()
}

pub fn os_capabilities() -> OSCapabilities {
    // Cache the version lookup for efficiency
    static OS_CAPABILITIES: OnceLock<OSCapabilities> = OnceLock::new();
    OS_CAPABILITIES.get_or_init(|| OSCapabilities::from_os_version(get_version())).clone()
}