use std::{
    cell::{RefCell, RefMut},
    collections::VecDeque,
    fmt::{self, Debug},
    mem,
    rc::{Rc, Weak},
    sync::{
        atomic::{AtomicBool, Ordering},
        Mutex, MutexGuard,
    },
    time::Instant,
};

use core_foundation::runloop::{CFRunLoopGetMain, CFRunLoopWakeUp};
use objc2::foundation::{is_main_thread, NSSize};
use objc2::rc::autoreleasepool;
use once_cell::sync::Lazy;

use super::appkit::{NSApp, NSApplication, NSApplicationActivationPolicy, NSEvent};
use crate::{
    dpi::LogicalSize,
    event::{Event, StartCause, WindowEvent},
    event_loop::{ControlFlow, EventLoopWindowTarget as RootWindowTarget},
    platform_impl::platform::{
        event::{EventProxy, EventWrapper},
        event_loop::PanicInfo,
        menu,
        observer::EventLoopWaker,
        util::Never,
        window::WinitWindow,
    },
    window::WindowId,
};

static HANDLER: Lazy<Handler> = Lazy::new(Default::default);

impl<'a, Never> Event<'a, Never> {
    fn userify<T: 'static>(self) -> Event<'a, T> {
        self.map_nonuser_event()
            // `Never` can't be constructed, so the `UserEvent` variant can't
            // be present here.
            .unwrap_or_else(|_| unreachable!())
    }
}

pub trait EventHandler: Debug {
    // Not sure probably it should accept Event<'static, Never>
    fn handle_nonuser_event(&mut self, event: Event<'_, Never>, control_flow: &mut ControlFlow);
    fn handle_user_events(&mut self, control_flow: &mut ControlFlow);
}

pub(crate) type Callback<T> =
    RefCell<dyn FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow)>;

struct EventLoopHandler<T: 'static> {
    callback: Weak<Callback<T>>,
    window_target: Rc<RootWindowTarget<T>>,
}

impl<T> EventLoopHandler<T> {
    fn with_callback<F>(&mut self, f: F)
    where
        F: FnOnce(
            &mut EventLoopHandler<T>,
            RefMut<'_, dyn FnMut(Event<'_, T>, &RootWindowTarget<T>, &mut ControlFlow)>,
        ),
    {
        if let Some(callback) = self.callback.upgrade() {
            let callback = callback.borrow_mut();
            (f)(self, callback);
        } else {
            panic!(
                "Tried to dispatch an event, but the event loop that \
                owned the event handler callback seems to be destroyed"
            );
        }
    }
}

impl<T> Debug for EventLoopHandler<T> {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("EventLoopHandler")
            .field("window_target", &self.window_target)
            .finish()
    }
}

impl<T> EventHandler for EventLoopHandler<T> {
    fn handle_nonuser_event(&mut self, event: Event<'_, Never>, control_flow: &mut ControlFlow) {
        self.with_callback(|this, mut callback| {
            if let ControlFlow::ExitWithCode(code) = *control_flow {
                let dummy = &mut ControlFlow::ExitWithCode(code);
                (callback)(event.userify(), &this.window_target, dummy);
            } else {
                (callback)(event.userify(), &this.window_target, control_flow);
            }
        });
    }

    fn handle_user_events(&mut self, control_flow: &mut ControlFlow) {
        self.with_callback(|this, mut callback| {
            for event in this.window_target.p.receiver.try_iter() {
                if let ControlFlow::ExitWithCode(code) = *control_flow {
                    let dummy = &mut ControlFlow::ExitWithCode(code);
                    (callback)(Event::UserEvent(event), &this.window_target, dummy);
                } else {
                    (callback)(Event::UserEvent(event), &this.window_target, control_flow);
                }
            }
        });
    }
}

#[derive(Default)]
struct Handler {
    ready: AtomicBool,
    in_callback: AtomicBool,
    control_flow: Mutex<ControlFlow>,
    control_flow_prev: Mutex<ControlFlow>,
    start_time: Mutex<Option<Instant>>,
    callback: Mutex<Option<Box<dyn EventHandler>>>,
    pending_events: Mutex<VecDeque<EventWrapper>>,
    pending_redraw: Mutex<Vec<WindowId>>,
    waker: Mutex<EventLoopWaker>,
}

unsafe impl Send for Handler {}
unsafe impl Sync for Handler {}

impl Handler {
    fn events(&self) -> MutexGuard<'_, VecDeque<EventWrapper>> {
        self.pending_events.lock().unwrap()
    }

    fn redraw(&self) -> MutexGuard<'_, Vec<WindowId>> {
        self.pending_redraw.lock().unwrap()
    }

    fn waker(&self) -> MutexGuard<'_, EventLoopWaker> {
        self.waker.lock().unwrap()
    }

    fn is_ready(&self) -> bool {
        self.ready.load(Ordering::Acquire)
    }

    fn set_ready(&self) {
        self.ready.store(true, Ordering::Release);
    }

    fn should_exit(&self) -> bool {
        matches!(
            *self.control_flow.lock().unwrap(),
            ControlFlow::ExitWithCode(_)
        )
    }

    fn get_control_flow_and_update_prev(&self) -> ControlFlow {
        let control_flow = self.control_flow.lock().unwrap();
        *self.control_flow_prev.lock().unwrap() = *control_flow;
        *control_flow
    }

    fn get_old_and_new_control_flow(&self) -> (ControlFlow, ControlFlow) {
        let old = *self.control_flow_prev.lock().unwrap();
        let new = *self.control_flow.lock().unwrap();
        (old, new)
    }

    fn get_start_time(&self) -> Option<Instant> {
        *self.start_time.lock().unwrap()
    }

    fn update_start_time(&self) {
        *self.start_time.lock().unwrap() = Some(Instant::now());
    }

    fn take_events(&self) -> VecDeque<EventWrapper> {
        mem::take(&mut *self.events())
    }

    fn should_redraw(&self) -> Vec<WindowId> {
        mem::take(&mut *self.redraw())
    }

    fn get_in_callback(&self) -> bool {
        self.in_callback.load(Ordering::Acquire)
    }

    fn set_in_callback(&self, in_callback: bool) {
        self.in_callback.store(in_callback, Ordering::Release);
    }

    fn handle_nonuser_event(&self, wrapper: EventWrapper) {
        if let Some(ref mut callback) = *self.callback.lock().unwrap() {
            match wrapper {
                EventWrapper::StaticEvent(event) => {
                    callback.handle_nonuser_event(event, &mut self.control_flow.lock().unwrap())
                }
                EventWrapper::EventProxy(proxy) => self.handle_proxy(proxy, callback),
            }
        }
    }

    fn handle_user_events(&self) {
        if let Some(ref mut callback) = *self.callback.lock().unwrap() {
            callback.handle_user_events(&mut self.control_flow.lock().unwrap());
        }
    }

    fn handle_scale_factor_changed_event(
        &self,
        callback: &mut Box<dyn EventHandler + 'static>,
        window: &WinitWindow,
        suggested_size: LogicalSize<f64>,
        scale_factor: f64,
    ) {
        let mut size = suggested_size.to_physical(scale_factor);
        let new_inner_size = &mut size;
        let event = Event::WindowEvent {
            window_id: WindowId(window.id()),
            event: WindowEvent::ScaleFactorChanged {
                scale_factor,
                new_inner_size,
            },
        };

        callback.handle_nonuser_event(event, &mut self.control_flow.lock().unwrap());

        let physical_size = *new_inner_size;
        let logical_size = physical_size.to_logical(scale_factor);
        let size = NSSize::new(logical_size.width, logical_size.height);
        window.setContentSize(size);
    }

    fn handle_proxy(&self, proxy: EventProxy, callback: &mut Box<dyn EventHandler + 'static>) {
        match proxy {
            EventProxy::DpiChangedProxy {
                window,
                suggested_size,
                scale_factor,
            } => self.handle_scale_factor_changed_event(
                callback,
                &window,
                suggested_size,
                scale_factor,
            ),
        }
    }
}

pub(crate) enum AppState {}

impl AppState {
    pub fn set_callback<T>(callback: Weak<Callback<T>>, window_target: Rc<RootWindowTarget<T>>) {
        *HANDLER.callback.lock().unwrap() = Some(Box::new(EventLoopHandler {
            callback,
            window_target,
        }));
    }

    pub fn exit() -> i32 {
        HANDLER.set_in_callback(true);
        HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::LoopDestroyed));
        HANDLER.set_in_callback(false);
        HANDLER.callback.lock().unwrap().take();
        if let ControlFlow::ExitWithCode(code) = HANDLER.get_old_and_new_control_flow().1 {
            code
        } else {
            0
        }
    }

    pub fn launched(
        activation_policy: NSApplicationActivationPolicy,
        create_default_menu: bool,
        activate_ignoring_other_apps: bool,
    ) {
        let app = NSApp();
        // We need to delay setting the activation policy and activating the app
        // until `applicationDidFinishLaunching` has been called. Otherwise the
        // menu bar is initially unresponsive on macOS 10.15.
        app.setActivationPolicy(activation_policy);

        window_activation_hack(&app);
        app.activateIgnoringOtherApps(activate_ignoring_other_apps);

        HANDLER.set_ready();
        HANDLER.waker().start();
        if create_default_menu {
            // The menubar initialization should be before the `NewEvents` event, to allow
            // overriding of the default menu even if it's created
            menu::initialize();
        }
        HANDLER.set_in_callback(true);
        HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::NewEvents(
            StartCause::Init,
        )));
        // NB: For consistency all platforms must emit a 'resumed' event even though macOS
        // applications don't themselves have a formal suspend/resume lifecycle.
        HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::Resumed));
        HANDLER.set_in_callback(false);
    }

    pub fn wakeup(panic_info: Weak<PanicInfo>) {
        let panic_info = panic_info
            .upgrade()
            .expect("The panic info must exist here. This failure indicates a developer error.");

        // Return when in callback due to https://github.com/rust-windowing/winit/issues/1779
        if panic_info.is_panicking() || !HANDLER.is_ready() || HANDLER.get_in_callback() {
            return;
        }
        let start = HANDLER.get_start_time().unwrap();
        let cause = match HANDLER.get_control_flow_and_update_prev() {
            ControlFlow::Poll => StartCause::Poll,
            ControlFlow::Wait => StartCause::WaitCancelled {
                start,
                requested_resume: None,
            },
            ControlFlow::WaitUntil(requested_resume) => {
                if Instant::now() >= requested_resume {
                    StartCause::ResumeTimeReached {
                        start,
                        requested_resume,
                    }
                } else {
                    StartCause::WaitCancelled {
                        start,
                        requested_resume: Some(requested_resume),
                    }
                }
            }
            ControlFlow::ExitWithCode(_) => StartCause::Poll, //panic!("unexpected `ControlFlow::Exit`"),
        };
        HANDLER.set_in_callback(true);
        HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::NewEvents(cause)));
        HANDLER.set_in_callback(false);
    }

    // This is called from multiple threads at present
    pub fn queue_redraw(window_id: WindowId) {
        let mut pending_redraw = HANDLER.redraw();
        if !pending_redraw.contains(&window_id) {
            pending_redraw.push(window_id);
        }
        unsafe {
            let rl = CFRunLoopGetMain();
            CFRunLoopWakeUp(rl);
        }
    }

    pub fn handle_redraw(window_id: WindowId) {
        // Redraw request might come out of order from the OS.
        // -> Don't go back into the callback when our callstack originates from there
        if !HANDLER.in_callback.swap(true, Ordering::AcqRel) {
            HANDLER
                .handle_nonuser_event(EventWrapper::StaticEvent(Event::RedrawRequested(window_id)));
            HANDLER.set_in_callback(false);
        }
    }

    pub fn queue_event(wrapper: EventWrapper) {
        if !is_main_thread() {
            panic!("Event queued from different thread: {wrapper:#?}");
        }
        HANDLER.events().push_back(wrapper);
    }

    pub fn cleared(panic_info: Weak<PanicInfo>) {
        let panic_info = panic_info
            .upgrade()
            .expect("The panic info must exist here. This failure indicates a developer error.");

        // Return when in callback due to https://github.com/rust-windowing/winit/issues/1779
        if panic_info.is_panicking() || !HANDLER.is_ready() || HANDLER.get_in_callback() {
            return;
        }

        HANDLER.set_in_callback(true);
        HANDLER.handle_user_events();
        for event in HANDLER.take_events() {
            HANDLER.handle_nonuser_event(event);
        }
        HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::MainEventsCleared));
        for window_id in HANDLER.should_redraw() {
            HANDLER
                .handle_nonuser_event(EventWrapper::StaticEvent(Event::RedrawRequested(window_id)));
        }
        HANDLER.handle_nonuser_event(EventWrapper::StaticEvent(Event::RedrawEventsCleared));
        HANDLER.set_in_callback(false);

        if HANDLER.should_exit() {
            let app = NSApp();
            autoreleasepool(|_| {
                app.stop(None);
                // To stop event loop immediately, we need to post some event here.
                app.postEvent_atStart(&NSEvent::dummy(), true);
            });
        }
        HANDLER.update_start_time();
        match HANDLER.get_old_and_new_control_flow() {
            (ControlFlow::ExitWithCode(_), _) | (_, ControlFlow::ExitWithCode(_)) => (),
            (old, new) if old == new => (),
            (_, ControlFlow::Wait) => HANDLER.waker().stop(),
            (_, ControlFlow::WaitUntil(instant)) => HANDLER.waker().start_at(instant),
            (_, ControlFlow::Poll) => HANDLER.waker().start(),
        }
    }
}

/// A hack to make activation of multiple windows work when creating them before
/// `applicationDidFinishLaunching:` / `Event::Event::NewEvents(StartCause::Init)`.
///
/// Alternative to this would be the user calling `window.set_visible(true)` in
/// `StartCause::Init`.
///
/// If this becomes too bothersome to maintain, it can probably be removed
/// without too much damage.
fn window_activation_hack(app: &NSApplication) {
    // TODO: Proper ordering of the windows
    app.windows().into_iter().for_each(|window| {
        // Call `makeKeyAndOrderFront` if it was called on the window in `WinitWindow::new`
        // This way we preserve the user's desired initial visiblity status
        // TODO: Also filter on the type/"level" of the window, and maybe other things?
        if window.isVisible() {
            trace!("Activating visible window");
            window.makeKeyAndOrderFront(None);
        } else {
            trace!("Skipping activating invisible window");
        }
    })
}