use std::ffi::c_void;
use std::panic::{AssertUnwindSafe, UnwindSafe};
use std::ptr;
use std::rc::Weak;
use std::time::Instant;

use core_foundation::base::{CFIndex, CFOptionFlags, CFRelease};
use core_foundation::date::CFAbsoluteTimeGetCurrent;
use core_foundation::runloop::{
    kCFRunLoopAfterWaiting, kCFRunLoopBeforeWaiting, kCFRunLoopCommonModes,
    kCFRunLoopExit, CFRunLoopActivity, CFRunLoopAddObserver, CFRunLoopAddTimer,
    CFRunLoopGetMain, CFRunLoopObserverCallBack, CFRunLoopObserverContext,
    CFRunLoopObserverCreate, CFRunLoopObserverRef, CFRunLoopRef, CFRunLoopTimerCreate,
    CFRunLoopTimerInvalidate, CFRunLoopTimerRef, CFRunLoopTimerSetNextFireDate,
    CFRunLoopWakeUp,
};
use objc2_foundation::MainThreadMarker;

use super::app_delegate::ApplicationDelegate;
use super::event_loop::{stop_app_on_panic, PanicInfo};
use super::ffi;

unsafe fn control_flow_handler<F>(panic_info: *mut c_void, f: F)
where
    F: FnOnce(Weak<PanicInfo>) + UnwindSafe,
{
    let info_from_raw = unsafe { Weak::from_raw(panic_info as *mut PanicInfo) };
    // Asserting unwind safety on this type should be fine because `PanicInfo` is
    // `RefUnwindSafe` and `Rc<T>` is `UnwindSafe` if `T` is `RefUnwindSafe`.
    let panic_info = AssertUnwindSafe(Weak::clone(&info_from_raw));
    // `from_raw` takes ownership of the data behind the pointer.
    // But if this scope takes ownership of the weak pointer, then
    // the weak pointer will get free'd at the end of the scope.
    // However we want to keep that weak reference around after the function.
    std::mem::forget(info_from_raw);

    let mtm = MainThreadMarker::new().unwrap();
    stop_app_on_panic(mtm, Weak::clone(&panic_info), move || {
        let _ = &panic_info;
        f(panic_info.0)
    });
}

// begin is queued with the highest priority to ensure it is processed before other observers
extern "C" fn control_flow_begin_handler(
    _: CFRunLoopObserverRef,
    activity: CFRunLoopActivity,
    panic_info: *mut c_void,
) {
    unsafe {
        control_flow_handler(panic_info, |panic_info| {
            #[allow(non_upper_case_globals)]
            match activity {
                kCFRunLoopAfterWaiting => {
                    // trace!("Triggered `CFRunLoopAfterWaiting`");
                    ApplicationDelegate::get(MainThreadMarker::new().unwrap())
                        .wakeup(panic_info);
                    // trace!("Completed `CFRunLoopAfterWaiting`");
                }
                _ => unreachable!(),
            }
        });
    }
}

// end is queued with the lowest priority to ensure it is processed after other observers
// without that, LoopExiting would  get sent after AboutToWait
extern "C" fn control_flow_end_handler(
    _: CFRunLoopObserverRef,
    activity: CFRunLoopActivity,
    panic_info: *mut c_void,
) {
    unsafe {
        control_flow_handler(panic_info, |panic_info| {
            #[allow(non_upper_case_globals)]
            match activity {
                kCFRunLoopBeforeWaiting => {
                    // trace!("Triggered `CFRunLoopBeforeWaiting`");
                    ApplicationDelegate::get(MainThreadMarker::new().unwrap())
                        .cleared(panic_info);
                    // trace!("Completed `CFRunLoopBeforeWaiting`");
                }
                kCFRunLoopExit => (), // unimplemented!(), // not expected to ever happen
                _ => unreachable!(),
            }
        });
    }
}

pub struct RunLoop(CFRunLoopRef);

impl RunLoop {
    pub unsafe fn get() -> Self {
        RunLoop(unsafe { CFRunLoopGetMain() })
    }

    #[allow(unused)]
    pub fn wakeup(&self) {
        unsafe { CFRunLoopWakeUp(self.0) }
    }

    unsafe fn add_observer(
        &self,
        flags: CFOptionFlags,
        priority: CFIndex,
        handler: CFRunLoopObserverCallBack,
        context: *mut CFRunLoopObserverContext,
    ) {
        let observer = unsafe {
            CFRunLoopObserverCreate(
                ptr::null_mut(),
                flags,
                ffi::TRUE, // Indicates we want this to run repeatedly
                priority,  // The lower the value, the sooner this will run
                handler,
                context,
            )
        };
        unsafe { CFRunLoopAddObserver(self.0, observer, kCFRunLoopCommonModes) };
    }
}

pub fn setup_control_flow_observers(panic_info: Weak<PanicInfo>) {
    unsafe {
        let mut context = CFRunLoopObserverContext {
            info: Weak::into_raw(panic_info) as *mut _,
            version: 0,
            retain: None,
            release: None,
            copyDescription: None,
        };
        let run_loop = RunLoop::get();
        run_loop.add_observer(
            kCFRunLoopAfterWaiting,
            CFIndex::MIN,
            control_flow_begin_handler,
            &mut context as *mut _,
        );
        run_loop.add_observer(
            kCFRunLoopExit | kCFRunLoopBeforeWaiting,
            CFIndex::MAX,
            control_flow_end_handler,
            &mut context as *mut _,
        );
    }
}

#[derive(Debug)]
pub struct EventLoopWaker {
    timer: CFRunLoopTimerRef,

    /// An arbitrary instant in the past, that will trigger an immediate wake
    /// We save this as the `next_fire_date` for consistency so we can
    /// easily check if the next_fire_date needs updating.
    start_instant: Instant,

    /// This is what the `NextFireDate` has been set to.
    /// `None` corresponds to `waker.stop()` and `start_instant` is used
    /// for `waker.start()`
    next_fire_date: Option<Instant>,
}

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

impl Default for EventLoopWaker {
    fn default() -> 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(CFRunLoopGetMain(), timer, kCFRunLoopCommonModes);
            EventLoopWaker {
                timer,
                start_instant: Instant::now(),
                next_fire_date: None,
            }
        }
    }
}

impl EventLoopWaker {
    pub fn stop(&mut self) {
        if self.next_fire_date.is_some() {
            self.next_fire_date = None;
            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MAX) }
        }
    }

    pub fn start(&mut self) {
        if self.next_fire_date != Some(self.start_instant) {
            self.next_fire_date = Some(self.start_instant);
            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MIN) }
        }
    }

    pub fn start_at(&mut self, instant: Option<Instant>) {
        let now = Instant::now();
        match instant {
            Some(instant) if now >= instant => {
                self.start();
            }
            Some(instant) => {
                if self.next_fire_date != Some(instant) {
                    self.next_fire_date = Some(instant);
                    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)
                    }
                }
            }
            None => {
                self.stop();
            }
        }
    }
}
