lyra-engine/lyra-game/src/events.rs

use std::{collections::{HashMap, VecDeque}, any::{TypeId, Any}, cell::RefCell};

use crate::{castable_any::CastableAny, plugin::Plugin};

pub trait Event: Clone + Send + Sync + 'static {}
impl<T: Clone + Send + Sync + 'static> Event for T {}

pub type Events<T> = VecDeque<T>;

pub struct EventQueue {
    events: HashMap<TypeId, RefCell<Box<dyn CastableAny>>>,
    event_write_queue: HashMap<TypeId, RefCell<Box<dyn CastableAny>>>
}

impl Default for EventQueue {
    fn default() -> Self {
        Self::new()
    }
}

impl EventQueue {
    pub fn new() -> Self {
        Self {
            event_write_queue: HashMap::new(),
            events: HashMap::new(),
        }
    }

    /// Trigger an event
    pub fn trigger_event<E>(&mut self, event: E)
    where
        E: Event
    {
        // the compiler wants me to explicit right here for some reason
        let default = || RefCell::new(Box::<Events::<E>>::default() as Box<dyn CastableAny>);

        // Get, or create, a list of events of this type
        let type_id = event.type_id();
        let mut events = self.event_write_queue.entry(type_id)
            .or_insert_with(default)
            .borrow_mut();

        // downcast resource as an events storage
        let e: &mut Events<E> = events.as_mut().as_any_mut().downcast_mut().unwrap();
        e.push_back(event);
    }

    // Clear events, this should happen at the start of every tick since events are cloned
    // before being given to the reader.
    pub fn update_events(&mut self) {
        self.events.clear();

        // get all keys of events
        let keys: Vec<TypeId> = self.event_write_queue.keys().copied().collect();

        // remove all elements from self.event_write_queue and insert them to events
        for k in keys.into_iter() {
            let v = self.event_write_queue.remove(&k).unwrap();
            self.events.insert(k, v);
        }
    }

    pub fn read_events<E>(&self) -> Option<Events<E>>
    where
        E: Event
    {
        if let Some(event ) = self.events.get(&TypeId::of::<E>()) {
            let eref = event.borrow();
            Some(eref.as_ref().as_any().downcast_ref::<Events<E>>().unwrap().clone())
        } else {
            None
        }
    }
}

#[derive(Default)]
pub struct EventsPlugin;

impl Plugin for EventsPlugin {
    fn setup(&self, game: &mut crate::game::Game) {
        game.world().add_resource(EventQueue::new());
    }
}