use parking_lot::RwLock;

use crate::{DataStore, StoreEvent};

// ---

// TODO(cmc): Not sure why I need the extra Box here, RwLock should be `?Sized`.
type SharedStoreSubscriber = RwLock<Box<dyn StoreSubscriber>>;

/// A [`StoreSubscriber`] subscribes to atomic changes from all [`DataStore`]s through [`StoreEvent`]s.
///
/// [`StoreSubscriber`]s can be used to build both secondary indices and trigger systems.
//
// TODO(#4204): StoreSubscriber should require SizeBytes so they can be part of memstats.
pub trait StoreSubscriber: std::any::Any + Send + Sync {
    /// Arbitrary name for the subscriber.
    ///
    /// Does not need to be unique.
    fn name(&self) -> String;

    /// Workaround for downcasting support, simply return `self`:
    /// ```ignore
    /// fn as_any(&self) -> &dyn std::any::Any {
    ///     self
    /// }
    /// ```
    fn as_any(&self) -> &dyn std::any::Any;

    /// Workaround for downcasting support, simply return `self`:
    /// ```ignore
    /// fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
    ///     self
    /// }
    /// ```
    fn as_any_mut(&mut self) -> &mut dyn std::any::Any;

    /// The core of this trait: get notified of changes happening in all [`DataStore`]s.
    ///
    /// This will be called automatically by the [`DataStore`] itself if the subscriber has been
    /// registered: [`DataStore::register_subscriber`].
    /// Or you might want to feed it [`StoreEvent`]s manually, depending on your use case.
    ///
    /// ## Example
    ///
    /// ```ignore
    /// fn on_events(&mut self, events: &[StoreEvent]) {
    ///     use re_data_store::StoreDiffKind;
    ///     for event in events {
    ///         match event.kind {
    ///             StoreDiffKind::Addition => println!("Row added: {}", event.row_id),
    ///             StoreDiffKind::Deletion => println!("Row removed: {}", event.row_id),
    ///         }
    ///     }
    /// }
    /// ```
    fn on_events(&mut self, events: &[StoreEvent]);
}

/// All registered [`StoreSubscriber`]s.
static SUBSCRIBERS: once_cell::sync::Lazy<RwLock<Vec<SharedStoreSubscriber>>> =
    once_cell::sync::Lazy::new(|| RwLock::new(Vec::new()));

#[derive(Debug, Clone, Copy)]
pub struct StoreSubscriberHandle(u32);

impl DataStore {
    /// Registers a [`StoreSubscriber`] so it gets automatically notified when data gets added and/or
    /// removed to/from a [`DataStore`].
    ///
    /// Refer to [`StoreEvent`]'s documentation for more information about these events.
    ///
    /// ## Scope
    ///
    /// Registered [`StoreSubscriber`]s are global scope: they get notified of all events from all
    /// existing [`DataStore`]s, including [`DataStore`]s created after the subscriber was registered.
    ///
    /// Use [`StoreEvent::store_id`] to identify the source of an event.
    ///
    /// ## Late registration
    ///
    /// Subscribers must be registered before a store gets created to guarantee that no events
    /// were missed.
    ///
    /// [`StoreEvent::event_id`] can be used to identify missing events.
    ///
    /// ## Ordering
    ///
    /// The order in which registered subscribers are notified is undefined and will likely become
    /// concurrent in the future.
    ///
    /// If you need a specific order across multiple subscribers, embed them into an orchestrating
    /// subscriber.
    //
    // TODO(cmc): send a compacted snapshot to late registerers for bootstrapping
    pub fn register_subscriber(subscriber: Box<dyn StoreSubscriber>) -> StoreSubscriberHandle {
        let mut subscribers = SUBSCRIBERS.write();
        subscribers.push(RwLock::new(subscriber));
        StoreSubscriberHandle(subscribers.len() as u32 - 1)
    }

    /// Passes a reference to the downcasted subscriber to the given `FnMut` callback.
    ///
    /// Returns `None` if the subscriber doesn't exist or downcasting failed.
    pub fn with_subscriber<V: StoreSubscriber, T, F: FnMut(&V) -> T>(
        StoreSubscriberHandle(handle): StoreSubscriberHandle,
        mut f: F,
    ) -> Option<T> {
        let subscribers = SUBSCRIBERS.read();
        subscribers.get(handle as usize).and_then(|subscriber| {
            let subscriber = subscriber.read();
            subscriber.as_any().downcast_ref::<V>().map(&mut f)
        })
    }

    /// Passes a reference to the downcasted subscriber to the given `FnOnce` callback.
    ///
    /// Returns `None` if the subscriber doesn't exist or downcasting failed.
    pub fn with_subscriber_once<V: StoreSubscriber, T, F: FnOnce(&V) -> T>(
        StoreSubscriberHandle(handle): StoreSubscriberHandle,
        f: F,
    ) -> Option<T> {
        let subscribers = SUBSCRIBERS.read();
        subscribers.get(handle as usize).and_then(|subscriber| {
            let subscriber = subscriber.read();
            subscriber.as_any().downcast_ref::<V>().map(f)
        })
    }

    /// Passes a mutable reference to the downcasted subscriber to the given callback.
    ///
    /// Returns `None` if the subscriber doesn't exist or downcasting failed.
    pub fn with_subscriber_mut<V: StoreSubscriber, T, F: FnMut(&mut V) -> T>(
        StoreSubscriberHandle(handle): StoreSubscriberHandle,
        mut f: F,
    ) -> Option<T> {
        let subscribers = SUBSCRIBERS.read();
        subscribers.get(handle as usize).and_then(|subscriber| {
            let mut subscriber = subscriber.write();
            subscriber.as_any_mut().downcast_mut::<V>().map(&mut f)
        })
    }

    /// Called by [`DataStore`]'s mutating methods to notify subscriber subscribers of upcoming events.
    pub(crate) fn on_events(events: &[StoreEvent]) {
        re_tracing::profile_function!();
        let subscribers = SUBSCRIBERS.read();
        // TODO(cmc): might want to parallelize at some point.
        for subscriber in subscribers.iter() {
            subscriber.write().on_events(events);
        }
    }
}

#[cfg(test)]
mod tests {
    use ahash::HashSet;

    use re_log_types::{
        example_components::{MyColor, MyIndex, MyPoint},
        DataRow, RowId, StoreId, TimePoint, Timeline,
    };

    use crate::{DataStore, GarbageCollectionOptions, StoreSubscriber};

    use super::*;

    /// A simple [`StoreSubscriber`] for test purposes that just accumulates [`StoreEvent`]s.
    #[derive(Debug)]
    struct AllEvents {
        store_ids: HashSet<StoreId>,
        events: Vec<StoreEvent>,
    }

    impl AllEvents {
        fn new(store_ids: impl IntoIterator<Item = StoreId>) -> Self {
            Self {
                store_ids: store_ids.into_iter().collect(),
                events: Vec::new(),
            }
        }
    }

    impl StoreSubscriber for AllEvents {
        fn name(&self) -> String {
            "rerun.testing.store_subscribers.AllEvents".into()
        }

        fn as_any(&self) -> &dyn std::any::Any {
            self
        }

        fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
            self
        }

        fn on_events(&mut self, events: &[StoreEvent]) {
            self.events.extend(
                events
                    .iter()
                    // NOTE: `cargo` implicitly runs tests in parallel!
                    .filter(|e| self.store_ids.contains(&e.store_id))
                    .cloned(),
            );
        }
    }

    #[test]
    fn store_subscriber() -> anyhow::Result<()> {
        let mut store1 = DataStore::new(
            re_log_types::StoreId::random(re_log_types::StoreKind::Recording),
            Default::default(),
        );
        let mut store2 = DataStore::new(
            re_log_types::StoreId::random(re_log_types::StoreKind::Recording),
            Default::default(),
        );

        let mut expected_events = Vec::new();

        let view = AllEvents::new([store1.id().clone(), store2.id().clone()]);
        let view_handle = DataStore::register_subscriber(Box::new(view));

        let timeline_frame = Timeline::new_sequence("frame");
        let timeline_other = Timeline::new_temporal("other");
        let timeline_yet_another = Timeline::new_sequence("yet_another");

        let row = DataRow::from_component_batches(
            RowId::new(),
            TimePoint::from_iter([
                (timeline_frame, 42),      //
                (timeline_other, 666),     //
                (timeline_yet_another, 1), //
            ]),
            "entity_a".into(),
            [&MyIndex::from_iter(0..10) as _],
        )?;

        expected_events.extend(store1.insert_row(&row));

        let row = {
            let num_instances = 3;
            let points: Vec<_> = (0..num_instances)
                .map(|i| MyPoint::new(0.0, i as f32))
                .collect();
            let colors = vec![MyColor::from(0xFF0000FF)];
            DataRow::from_component_batches(
                RowId::new(),
                TimePoint::from_iter([
                    (timeline_frame, 42),      //
                    (timeline_yet_another, 1), //
                ]),
                "entity_b".into(),
                [&points as _, &colors as _],
            )?
        };

        expected_events.extend(store2.insert_row(&row));

        let row = {
            let num_instances = 6;
            let colors = vec![MyColor::from(0x00DD00FF); num_instances];
            DataRow::from_component_batches(
                RowId::new(),
                TimePoint::default(),
                "entity_b".into(),
                [
                    &MyIndex::from_iter(0..num_instances as _) as _,
                    &colors as _,
                ],
            )?
        };

        expected_events.extend(store1.insert_row(&row));

        expected_events.extend(store1.gc(&GarbageCollectionOptions::gc_everything()).0);
        expected_events.extend(store2.gc(&GarbageCollectionOptions::gc_everything()).0);

        DataStore::with_subscriber::<AllEvents, _, _>(view_handle, |got| {
            similar_asserts::assert_eq!(expected_events.len(), got.events.len());
            similar_asserts::assert_eq!(expected_events, got.events);
        });

        Ok(())
    }
}