//! Resting place for the reference-based [MmapLog] Zero-Copy Multi Channel

use crate::{
    ogre_std::ogre_queues::{
            meta_topic::MetaTopic,
            log_topics::mmap_meta::MMapMeta,
            meta_publisher::MetaPublisher,
            meta_subscriber::MetaSubscriber,
            log_topics::mmap_meta::MMapMetaSubscriber,
        },
    types::{ChannelCommon, ChannelMulti, ChannelProducer, ChannelConsumer, FullDuplexMultiChannel},
    streams_manager::StreamsManagerBase,
    mutiny_stream::MutinyStream,
};
use std::{
    time::Duration,
    sync::Arc,
    fmt::Debug,
    task::Waker,
};
use std::future::Future;


const BUFFER_SIZE: usize = 1<<38;

/// ...
pub struct MmapLog<'a, ItemType:          Send + Sync + Debug,
                       const MAX_STREAMS: usize = 16> {

    /// common code for dealing with streams
    streams_manager:     StreamsManagerBase<MAX_STREAMS>,
    /// backing storage for events
    log_queue:           Arc<MMapMeta<'a, ItemType>>,
    /// tracking of each Stream's next event to send
    subscribers:         [MMapMetaSubscriber<'a, ItemType>; MAX_STREAMS],
}

impl<'a, ItemType:          Send + Sync + Debug + 'a,
         const MAX_STREAMS: usize>
MmapLog<'a, ItemType, MAX_STREAMS> {

    /// NOTE: currently the file contents are ignored, but this is to change in the future: we should continue from where we left
    fn from_file<IntoString: Into<String>>(mmap_file_path: IntoString) -> Result<Arc<Self>, Box<dyn std::error::Error>> {
        let mmap_file_path = mmap_file_path.into();
        let log_queue = MMapMeta::new(&mmap_file_path, BUFFER_SIZE as u64)
            .map_err(|err| format!("`mmap_log` channel couldn't mmap file '{mmap_file_path}': {err}"))?;
        Ok(Arc::new(Self {
            streams_manager: StreamsManagerBase::new(mmap_file_path),
            log_queue:       log_queue.clone(),
            subscribers:     [0; MAX_STREAMS].map(|_| MMapMetaSubscriber::Dynamic(log_queue.subscribe_to_new_events_only())),    // TODO 2023-05-28: Option<> to avoid unnecessary setting the values here?
        }))
    }
}

impl<'a, ItemType:          Send + Sync + Debug + 'a,
         const MAX_STREAMS: usize>
ChannelCommon<ItemType, &'static ItemType> for
MmapLog<'a, ItemType, MAX_STREAMS> {

    /// IMPLEMENTATION NOTE: use Self::from_file() instead for better control over the mmap file name and error handling
    fn new<IntoString: Into<String>>(name: IntoString) -> Arc<Self> {
        let name = name.into();
        let mmap_file_path = format!("/tmp/{}.mmap", name.chars().map(|c| if c == ' ' || c >= '0' || c <= '9' || c >= 'A' || c <= 'z' { c } else { '_' }).collect::<String>());
        Self::from_file(mmap_file_path).unwrap()
    }

    async fn flush(&self, timeout: Duration) -> u32 {
        self.streams_manager.flush(timeout, || self.pending_items_count()).await
    }

    #[inline(always)]
    fn is_channel_open(&self) -> bool {
        self.streams_manager.is_any_stream_running()
    }

    async fn gracefully_end_stream(&self, stream_id: u32, timeout: Duration) -> bool {
        self.streams_manager.end_stream(stream_id, timeout, || self.pending_items_count()).await
    }

    async fn gracefully_end_all_streams(&self, timeout: Duration) -> u32 {
        self.streams_manager.end_all_streams(timeout, || self.pending_items_count()).await
    }

    fn cancel_all_streams(&self) {
        self.streams_manager.cancel_all_streams();
    }

    #[inline(always)]
    fn running_streams_count(&self) -> u32 {
        self.streams_manager.running_streams_count()
    }

    #[inline(always)]
    fn pending_items_count(&self) -> u32 {
        self.streams_manager.used_streams().iter()
            .take_while(|&&stream_id| stream_id != u32::MAX)
            .map(|&stream_id| unsafe { self.subscribers.get_unchecked(stream_id as usize) }.remaining_elements_count())
            .max().unwrap_or(0) as u32
    }

    #[inline(always)]
    fn buffer_size(&self) -> u32 {
        u32::MAX
    }
}


impl<'a, ItemType:          Send + Sync + Debug + 'a,
         const MAX_STREAMS: usize>
ChannelMulti<'a, ItemType, &'static ItemType> for
MmapLog<'a, ItemType, MAX_STREAMS> {

    fn create_stream_for_old_events(self: &Arc<Self>) -> (MutinyStream<'a, ItemType, Self, &'static ItemType>, u32) where Self: ChannelConsumer<'a, &'static ItemType> {
        let ref_self: &Self = self;
        let mutable_self = unsafe { &mut *(*(ref_self as *const Self as *const std::cell::UnsafeCell<Self>)).get() };
        let stream_id = self.streams_manager.create_stream_id();
        mutable_self.subscribers[stream_id as usize] = MMapMetaSubscriber::Fixed(self.log_queue.subscribe_to_old_events_only());
        (MutinyStream::new(stream_id, self), stream_id)
    }

    fn create_stream_for_new_events(self: &Arc<Self>) -> (MutinyStream<'a, ItemType, Self, &'static ItemType>, u32) {
        let ref_self: &Self = self;
        let mutable_self = unsafe { &mut *(*(ref_self as *const Self as *const std::cell::UnsafeCell<Self>)).get() };
        let stream_id = self.streams_manager.create_stream_id();
        mutable_self.subscribers[stream_id as usize] = MMapMetaSubscriber::Dynamic(self.log_queue.subscribe_to_new_events_only());
        (MutinyStream::new(stream_id, self), stream_id)
    }

    fn create_streams_for_old_and_new_events(self: &Arc<Self>) -> ((MutinyStream<'a, ItemType, Self, &'static ItemType>, u32), (MutinyStream<'a, ItemType, Self, &'static ItemType>, u32)) where Self: ChannelConsumer<'a, &'static ItemType> {
        let ref_self: &Self = self;
        let mutable_self = unsafe { &mut *(*(ref_self as *const Self as *const std::cell::UnsafeCell<Self>)).get() };
        let (stream_of_oldies, stream_of_newies) = self.log_queue.subscribe_to_separated_old_and_new_events();
        let stream_of_oldies_id = self.streams_manager.create_stream_id();
        let stream_of_newies_id = self.streams_manager.create_stream_id();
        mutable_self.subscribers[stream_of_oldies_id as usize] = MMapMetaSubscriber::Fixed(stream_of_oldies);
        mutable_self.subscribers[stream_of_newies_id as usize] = MMapMetaSubscriber::Dynamic(stream_of_newies);
        ( (MutinyStream::new(stream_of_oldies_id, self), stream_of_oldies_id),
          (MutinyStream::new(stream_of_newies_id, self), stream_of_newies_id) )
    }

    fn create_stream_for_old_and_new_events(self: &Arc<Self>) -> (MutinyStream<'a, ItemType, Self, &'static ItemType>, u32) where Self: ChannelConsumer<'a, &'static ItemType> {
        let ref_self: &Self = self;
        let mutable_self = unsafe { &mut *(*(ref_self as *const Self as *const std::cell::UnsafeCell<Self>)).get() };
        let stream_id = self.streams_manager.create_stream_id();
        mutable_self.subscribers[stream_id as usize] = MMapMetaSubscriber::Dynamic(self.log_queue.subscribe_to_joined_old_and_new_events());
        (MutinyStream::new(stream_id, self), stream_id)
    }
}


impl<'a, ItemType:          'a + Send + Sync + Debug,
         const MAX_STREAMS: usize>
ChannelProducer<'a, ItemType, &'static ItemType> for
MmapLog<'a, ItemType, MAX_STREAMS> {

    #[inline(always)]
    fn send(&self, item: ItemType) -> keen_retry::RetryConsumerResult<(), ItemType, ()> {
        match self.log_queue.publish_movable(item) {
            (Some(_tail), _none_item) => {
                let running_streams_count = self.streams_manager.running_streams_count();
                let used_streams = self.streams_manager.used_streams();
                for i in 0..running_streams_count {
                    let stream_id = *unsafe { used_streams.get_unchecked(i as usize) };
                    if stream_id != u32::MAX {
                        self.streams_manager.wake_stream(stream_id);
                    }
                }
                keen_retry::RetryResult::Ok { reported_input: (), output: () }
            },
            (None, some_item) => {
                keen_retry::RetryResult::Transient { input: some_item.expect("reactive-mutiny: mmap_log::send() BUG! None `some_item`"), error: () }
            }
        }
    }

    #[inline(always)]
    fn send_with<F: FnOnce(&mut ItemType)>(&self, setter: F) -> keen_retry::RetryConsumerResult<(), F, ()> {
        match self.log_queue.publish(setter) {
            (Some(_tail), _none_setter) => {
                let running_streams_count = self.streams_manager.running_streams_count();
                let used_streams = self.streams_manager.used_streams();
                // TODO 2024-03-05: can this Stream awakening be optimized, like on the zero-copy channels? Tests should prove it.
                for i in 0..running_streams_count {
                    let stream_id = *unsafe { used_streams.get_unchecked(i as usize) };
                    if stream_id != u32::MAX {
                        self.streams_manager.wake_stream(stream_id);
                    }
                }
                keen_retry::RetryResult::Ok { reported_input: (), output: () }
            },
            (None, some_setter) => {
                keen_retry::RetryResult::Transient { input: some_setter.expect("reactive-mutiny: mmap_log::send_with() BUG! None `some_setter`"), error: () }
            },
        }
    }

    #[inline(always)]
    async fn send_with_async<F:   FnOnce(&'a mut ItemType) -> Fut,
                             Fut: Future<Output=&'a mut ItemType>>
                            (&'a self,
                             setter: F) -> keen_retry::RetryConsumerResult<(), F, ()> {
        if let Some((slot, _slot_id)) = self.log_queue.leak_slot() {
            let slot = setter(slot).await;
            self.log_queue.publish_leaked_ref(slot);
            let running_streams_count = self.streams_manager.running_streams_count();
            let used_streams = self.streams_manager.used_streams();
            // TODO 2024-03-05: can this Stream awakening be optimized, like on the zero-copy channels? Tests should prove it.
            for i in 0..running_streams_count {
                let stream_id = *unsafe { used_streams.get_unchecked(i as usize) };
                if stream_id != u32::MAX {
                    self.streams_manager.wake_stream(stream_id);
                }
            }
            keen_retry::RetryResult::Ok { reported_input: (), output: () }
        } else {
            keen_retry::RetryResult::Transient { input: setter, error: () }
        }
    }

    #[inline(always)]
    fn send_derived(&self, _derived_item: &&'static ItemType) -> bool {
        todo!("reactive_mutiny::multi::channels::references::MMapLog: `send_derived()` is not implemented for the MMapLog Multi channel '{}' -- it doesn't make sense to place a reference in an mmap", self.streams_manager.name())
    }

    #[inline(always)]
    fn reserve_slot(&'a self) -> Option<&'a mut ItemType> {
        self.log_queue.leak_slot()
            .map(|(slot_ref, _slot_id)| slot_ref)
    }

    #[inline(always)]
    fn try_send_reserved(&self, reserved_slot: &mut ItemType) -> bool {
        self.log_queue.publish_leaked_ref(reserved_slot).is_some()
    }

    #[inline(always)]
    fn try_cancel_slot_reserve(&self, reserved_slot: &mut ItemType) -> bool {
        self.log_queue.unleak_slot_ref(reserved_slot);
        todo!("Complete this implementation");
    }
}


impl<'a, ItemType:          'a + Send + Sync + Debug,
         const MAX_STREAMS: usize>
ChannelConsumer<'a, &'static ItemType>
for MmapLog<'a, ItemType, MAX_STREAMS> {

    #[inline(always)]
    fn consume(&self, stream_id: u32) -> Option<&'static ItemType> {
        let subscriber = unsafe { self.subscribers.get_unchecked(stream_id as usize) };
        match subscriber {

            // dynamic subscriber -- for new events (may include old events as well -- in a continuous stream): yields events until interrupted
            MMapMetaSubscriber::Dynamic(subscriber) => {
                subscriber.consume(|slot| unsafe {&*(slot as *const ItemType)},
                                   || false,
                                   |_len_after| {})
            },

            // fixed subscriber -- for old-only events: once the first empty event is consumed, it is over (interrupts itself automatically)
            MMapMetaSubscriber::Fixed(subscriber) => {
                subscriber.consume(|slot| unsafe {&*(slot as *const ItemType)},
                                   || {
                                       self.streams_manager.cancel_stream(stream_id);
                                       false
                                   },
                                   |_len_after| {})
            },

        }

    }

    #[inline(always)]
    fn keep_stream_running(&self, stream_id: u32) -> bool {
        self.streams_manager.keep_stream_running(stream_id)
    }

    #[inline(always)]
    fn register_stream_waker(&self, stream_id: u32, waker: &Waker) {
        self.streams_manager.register_stream_waker(stream_id, waker)
    }

    #[inline(always)]
    fn drop_resources(&self, stream_id: u32) {
        self.streams_manager.report_stream_dropped(stream_id);
    }
}


impl<'a, ItemType:          Send + Sync + Debug + 'a,
         const MAX_STREAMS: usize>
Drop for
MmapLog<'a, ItemType, MAX_STREAMS> {
    fn drop(&mut self) {
        self.streams_manager.cancel_all_streams();
    }
}


impl <ItemType:          'static + Debug + Send + Sync,
      const MAX_STREAMS: usize>
FullDuplexMultiChannel for
MmapLog<'static, ItemType, MAX_STREAMS> {

    const MAX_STREAMS: usize = MAX_STREAMS;
    const BUFFER_SIZE: usize = BUFFER_SIZE;
    type ItemType            = ItemType;
    type DerivedItemType     = &'static ItemType;
}