use either::Either;
/*
This file is modified from the original file in the following repo:
https://github.com/zed-industries/zed


Copyright 2022 - 2024 Zed Industries, Inc.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at


       http://www.apache.org/licenses/LICENSE-2.0


   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.




Apache License
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                        http://www.apache.org/licenses/


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*/
use crate::sync::{thread, AtomicBool, Mutex};
use smallvec::SmallVec;
use std::collections::{BTreeMap, BTreeSet};
use std::sync::atomic::Ordering;
use std::sync::{Arc, Weak};
use std::{fmt::Debug, mem};
use thread::ThreadId;

#[derive(Debug)]
pub enum SubscriptionError {
    CannotEmitEventDueToRecursiveCall,
}

impl std::fmt::Display for Subscription {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "SubscriptionError")
    }
}

pub struct SubscriberSet<EmitterKey, Callback>(
    Arc<Mutex<SubscriberSetState<EmitterKey, Callback>>>,
);

impl<EmitterKey, Callback> Clone for SubscriberSet<EmitterKey, Callback> {
    fn clone(&self) -> Self {
        SubscriberSet(self.0.clone())
    }
}

struct SubscriberSetState<EmitterKey, Callback> {
    subscribers: BTreeMap<EmitterKey, Either<BTreeMap<usize, Subscriber<Callback>>, ThreadId>>,
    dropped_subscribers: BTreeSet<(EmitterKey, usize)>,
    next_subscriber_id: usize,
}

struct Subscriber<Callback> {
    active: Arc<AtomicBool>,
    callback: Callback,
    /// This field is used to drop the subscription when the subscriber is dropped.
    _sub: InnerSubscription,
}

impl<EmitterKey, Callback> SubscriberSet<EmitterKey, Callback>
where
    EmitterKey: 'static + Ord + Clone + Debug + Send + Sync,
    Callback: 'static + Send + Sync,
{
    pub fn new() -> Self {
        Self(Arc::new(Mutex::new(SubscriberSetState {
            subscribers: Default::default(),
            dropped_subscribers: Default::default(),
            next_subscriber_id: 0,
        })))
    }

    /// Inserts a new [`Subscription`] for the given `emitter_key`.
    ///
    /// By default, subscriptions are inert, meaning that they won't be listed when calling
    /// `[SubscriberSet::remove]` or `[SubscriberSet::retain]`. This method returns a tuple
    /// of a [`Subscription`] and an `impl FnOnce`, and you can use the latter to activate
    /// the [`Subscription`].
    pub fn insert(
        &self,
        emitter_key: EmitterKey,
        callback: Callback,
    ) -> (Subscription, impl FnOnce()) {
        let active = Arc::new(AtomicBool::new(false));
        let mut lock = self.0.lock();
        let subscriber_id = post_inc(&mut lock.next_subscriber_id);
        let this = Arc::downgrade(&self.0);
        let emitter_key_1 = emitter_key.clone();
        let inner_sub = InnerSubscription {
            unsubscribe: Arc::new(Mutex::new(Some(Box::new(move || {
                let Some(this) = this.upgrade() else {
                    return;
                };

                let mut lock = this.lock();
                let Some(subscribers) = lock.subscribers.get_mut(&emitter_key) else {
                    // remove was called with this emitter_key
                    return;
                };

                if let Either::Left(subscribers) = subscribers {
                    subscribers.remove(&subscriber_id);
                    if subscribers.is_empty() {
                        lock.subscribers.remove(&emitter_key);
                    }
                    return;
                }

                // We didn't manage to remove the subscription, which means it was dropped
                // while invoking the callback. Mark it as dropped so that we can remove it
                // later.
                lock.dropped_subscribers
                    .insert((emitter_key, subscriber_id));
            })))),
        };
        let subscription = Subscription {
            unsubscribe: Arc::downgrade(&inner_sub.unsubscribe),
        };

        lock.subscribers
            .entry(emitter_key_1)
            .or_insert_with(|| Either::Left(BTreeMap::new()))
            .as_mut()
            .unwrap_left()
            .insert(
                subscriber_id,
                Subscriber {
                    active: active.clone(),
                    callback,
                    _sub: inner_sub,
                },
            );
        (subscription, move || active.store(true, Ordering::Relaxed))
    }

    #[allow(unused)]
    pub fn remove(&self, emitter: &EmitterKey) -> impl IntoIterator<Item = Callback> {
        let mut lock = self.0.lock();
        let subscribers = lock.subscribers.remove(emitter);
        subscribers
            .and_then(|x| x.left().map(|s| s.into_values()))
            .into_iter()
            .flatten()
            .filter_map(|subscriber| {
                if subscriber.active.load(Ordering::Relaxed) {
                    Some(subscriber.callback)
                } else {
                    None
                }
            })
    }

    pub fn is_recursive_calling(&self, emitter: &EmitterKey) -> bool {
        if let Some(Either::Right(thread_id)) = self.0.lock().subscribers.get(emitter) {
            *thread_id == thread::current().id()
        } else {
            false
        }
    }

    /// Call the given callback for each subscriber to the given emitter.
    /// If the callback returns false, the subscriber is removed.
    pub fn retain(
        &self,
        emitter: &EmitterKey,
        f: &mut dyn FnMut(&mut Callback) -> bool,
    ) -> Result<(), SubscriptionError> {
        let mut subscribers = {
            let inner = loop {
                let mut subscriber_set_state = self.0.lock();
                let Some(set) = subscriber_set_state.subscribers.get_mut(emitter) else {
                    return Ok(());
                };
                match set {
                    Either::Left(_) => {
                        break std::mem::replace(set, Either::Right(thread::current().id()))
                            .unwrap_left();
                    }
                    Either::Right(lock_thread) => {
                        if thread::current().id() == *lock_thread {
                            return Err(SubscriptionError::CannotEmitEventDueToRecursiveCall);
                        } else {
                            // return Ok(());
                            drop(subscriber_set_state);
                            #[cfg(loom)]
                            loom::thread::yield_now();
                            #[cfg(not(loom))]
                            std::thread::sleep(std::time::Duration::from_millis(10));
                        }
                    }
                }
            };
            inner
        };

        subscribers.retain(|_, subscriber| {
            if subscriber.active.load(Ordering::Relaxed) {
                f(&mut subscriber.callback)
            } else {
                true
            }
        });

        let mut lock = self.0.lock();

        // Add any new subscribers that were added while invoking the callback.
        if let Some(Either::Left(new_subscribers)) = lock.subscribers.remove(emitter) {
            subscribers.extend(new_subscribers);
        }

        // Remove any dropped subscriptions that were dropped while invoking the callback.
        for (dropped_emitter, dropped_subscription_id) in mem::take(&mut lock.dropped_subscribers) {
            if *emitter == dropped_emitter {
                subscribers.remove(&dropped_subscription_id);
            } else {
                lock.dropped_subscribers
                    .insert((dropped_emitter, dropped_subscription_id));
            }
        }

        lock.subscribers
            .insert(emitter.clone(), Either::Left(subscribers));
        Ok(())
    }

    pub fn is_empty(&self) -> bool {
        self.0.lock().subscribers.is_empty()
    }

    pub fn may_include(&self, emitter: &EmitterKey) -> bool {
        self.0.lock().subscribers.contains_key(emitter)
    }
}

impl<EmitterKey, Callback> Default for SubscriberSet<EmitterKey, Callback>
where
    EmitterKey: 'static + Ord + Clone + Debug + Send + Sync,
    Callback: 'static + Send + Sync,
{
    fn default() -> Self {
        Self::new()
    }
}

impl<EmitterKey, Callback> std::fmt::Debug for SubscriberSet<EmitterKey, Callback>
where
    EmitterKey: 'static + Ord + Clone + Debug + Send + Sync,
    Callback: 'static + Send + Sync,
{
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let lock = self.0.lock();
        f.debug_struct("SubscriberSet")
            .field("subscriber_count", &lock.subscribers.len())
            .field("dropped_subscribers_count", &lock.dropped_subscribers.len())
            .field("next_subscriber_id", &lock.next_subscriber_id)
            .finish()
    }
}

fn post_inc(next_subscriber_id: &mut usize) -> usize {
    let ans = *next_subscriber_id;
    *next_subscriber_id += 1;
    ans
}
type Callback = Box<dyn FnOnce() + 'static + Send + Sync>;

/// A handle to a subscription created by GPUI. When dropped, the subscription
/// is cancelled and the callback will no longer be invoked.
#[must_use]
pub struct Subscription {
    unsubscribe: Weak<Mutex<Option<Callback>>>,
}

impl std::fmt::Debug for Subscription {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Subscription").finish()
    }
}

impl Subscription {
    /// Detaches the subscription from this handle. The callback will
    /// continue to be invoked until the doc has been subscribed to
    /// are dropped
    pub fn detach(self) {
        if let Some(unsubscribe) = self.unsubscribe.upgrade() {
            unsubscribe.lock().take();
        }
    }

    /// Unsubscribes the subscription.
    #[inline]
    pub fn unsubscribe(self) {
        drop(self)
    }
}

impl Drop for Subscription {
    fn drop(&mut self) {
        if let Some(unsubscribe) = self.unsubscribe.upgrade() {
            let unsubscribe = unsubscribe.lock().take();
            if let Some(unsubscribe) = unsubscribe {
                unsubscribe();
            }
        }
    }
}

struct InnerSubscription {
    unsubscribe: Arc<Mutex<Option<Callback>>>,
}

impl Drop for InnerSubscription {
    fn drop(&mut self) {
        self.unsubscribe.lock().take();
    }
}

/// A wrapper around `SubscriberSet` that automatically handles recursive event emission.
///
/// This struct differs from `SubscriberSet` in the following ways:
/// 1. It automatically handles the `CannotEmitEventDueToRecursiveCall` error that can occur in `SubscriberSet`.
/// 2. When a recursive event emission is detected, it queues the event instead of throwing an error.
/// 3. After the current event processing is complete, it automatically processes the queued events.
///
/// This behavior ensures that all events are processed in the order they were emitted, even in cases
/// where recursive event emission would normally cause an error.
#[derive(Clone)]
pub struct SubscriberSetWithQueue<EmitterKey, Callback, Payload> {
    subscriber_set: SubscriberSet<EmitterKey, Callback>,
    queue: Arc<Mutex<BTreeMap<EmitterKey, Vec<Payload>>>>,
}

impl<EmitterKey, Callback, Payload> Debug
    for SubscriberSetWithQueue<EmitterKey, Callback, Payload>
{
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("SubscriberSetWithQueue").finish()
    }
}

impl<EmitterKey, Callback, Payload> Default
    for SubscriberSetWithQueue<EmitterKey, Callback, Payload>
where
    EmitterKey: 'static + Ord + Clone + Debug + Send + Sync,
    Callback: 'static + Send + Sync + for<'a> FnMut(&'a Payload) -> bool,
    Payload: Send + Sync + Debug,
{
    fn default() -> Self {
        Self::new()
    }
}

pub struct WeakSubscriberSetWithQueue<EmitterKey, Callback, Payload> {
    subscriber_set: Weak<Mutex<SubscriberSetState<EmitterKey, Callback>>>,
    queue: Weak<Mutex<BTreeMap<EmitterKey, Vec<Payload>>>>,
}

impl<EmitterKey, Callback, Payload> Debug
    for WeakSubscriberSetWithQueue<EmitterKey, Callback, Payload>
{
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("WeakSubscriberSetWithQueue").finish()
    }
}

impl<EmitterKey, Callback, Payload> Clone
    for WeakSubscriberSetWithQueue<EmitterKey, Callback, Payload>
{
    fn clone(&self) -> Self {
        Self {
            subscriber_set: self.subscriber_set.clone(),
            queue: self.queue.clone(),
        }
    }
}

impl<EmitterKey, Callback, Payload> WeakSubscriberSetWithQueue<EmitterKey, Callback, Payload> {
    pub fn upgrade(self) -> Option<SubscriberSetWithQueue<EmitterKey, Callback, Payload>> {
        Some(SubscriberSetWithQueue {
            subscriber_set: SubscriberSet(self.subscriber_set.upgrade()?),
            queue: self.queue.upgrade()?,
        })
    }
}

impl<EmitterKey, Callback, Payload> SubscriberSetWithQueue<EmitterKey, Callback, Payload>
where
    EmitterKey: 'static + Ord + Clone + Debug + Send + Sync,
    Callback: 'static + Send + Sync + for<'a> FnMut(&'a Payload) -> bool,
    Payload: Send + Sync + Debug,
{
    pub fn new() -> Self {
        Self {
            subscriber_set: SubscriberSet::new(),
            queue: Arc::new(Mutex::new(Default::default())),
        }
    }

    pub fn downgrade(&self) -> WeakSubscriberSetWithQueue<EmitterKey, Callback, Payload> {
        WeakSubscriberSetWithQueue {
            subscriber_set: Arc::downgrade(&self.subscriber_set.0),
            queue: Arc::downgrade(&self.queue),
        }
    }

    pub fn inner(&self) -> &SubscriberSet<EmitterKey, Callback> {
        &self.subscriber_set
    }

    pub fn emit(&self, key: &EmitterKey, payload: Payload) {
        let mut pending_events: SmallVec<[Payload; 1]> = SmallVec::new();
        pending_events.push(payload);
        while let Some(payload) = pending_events.pop() {
            let result = self
                .subscriber_set
                .retain(key, &mut |callback| (callback)(&payload));
            match result {
                Ok(_) => {
                    let mut queue = self.queue.lock();
                    if let Some(new_pending_events) = queue.remove(key) {
                        pending_events.extend(new_pending_events);
                    }
                }
                Err(SubscriptionError::CannotEmitEventDueToRecursiveCall) => {
                    let mut queue = self.queue.lock();
                    queue.entry(key.clone()).or_default().push(payload);
                }
            }
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_inner_subscription_drop() {
        let subscriber_set = SubscriberSet::<i32, Box<dyn Fn(&i32) -> bool + Send + Sync>>::new();
        let (subscription, activate) = subscriber_set.insert(1, Box::new(move |_: &i32| true));
        activate();
        drop(subscriber_set);
        assert!(subscription.unsubscribe.upgrade().is_none());
    }

    #[test]
    fn test_inner_subscription_drop_2() {
        let subscriber_set = SubscriberSet::<i32, Box<dyn Fn(&i32) -> bool + Send + Sync>>::new();
        let (subscription, activate) = subscriber_set.insert(1, Box::new(move |_: &i32| false));
        activate();
        subscriber_set
            .retain(&1, &mut |callback| callback(&1))
            .unwrap();
        assert!(subscription.unsubscribe.upgrade().is_none());
    }
}
