engine/ecs/src/events.rs

use std::{
    any::{Any, TypeId},
    collections::HashMap,
    ops::DerefMut,
    sync::Arc,
};

use crate::World;

pub struct Events {
    events: HashMap<
        TypeId, // TypeId of Payload
        (
            Vec<Box<dyn Any + Send + Sync>>, // Payload
            Vec<Arc<dyn Fn(&mut World, &dyn Any) -> anyhow::Result<()> + Send + Sync>>, // Listener on Payload
        ),
    >,
}

impl Default for Events {
    fn default() -> Self {
        Self {
            events: HashMap::new(),
        }
    }
}

impl Events {
    pub(crate) fn take_events(&mut self) -> Self {
        Self {
            events: self
                .events
                .iter_mut()
                .filter_map(|(type_id, (payload, listener))| {
                    (!payload.is_empty())
                        .then(|| (*type_id, (std::mem::take(payload), listener.clone())))
                })
                .collect(),
        }
    }

    pub fn clear(&mut self) {
        for (payloads, listener) in self.events.values_mut() {
            payloads.clear();
            listener.clear();
        }
    }

    pub fn register_event<T: Any + Send + Sync>(&mut self) {
        self.events
            .insert(TypeId::of::<T>(), (Vec::new(), Vec::new()));
    }

    pub fn add_reader<T: Any + Send + Sync, F>(&mut self, f: F)
    where
        F: Fn(&mut World, &T) -> anyhow::Result<()> + Send + Sync + 'static,
    {
        match self.events.get_mut(&TypeId::of::<T>()) {
            Some((_, listener)) => listener.push(Arc::new(move |world, payload| {
                let typed_payload: &T = payload.downcast_ref().unwrap();

                f(world, typed_payload)
            })),
            None => panic!("register event type first!"),
        }
    }

    pub fn write_event<T: Any + Send + Sync>(&mut self, payload: T) {
        match self.events.get_mut(&TypeId::of::<T>()) {
            Some((payloads, _)) => payloads.push(Box::new(payload)),
            None => panic!("register event type first!"),
        }
    }

    pub(crate) fn fire_events(&mut self, world: &mut World) -> anyhow::Result<()> {
        for (payloads, listeners) in self.events.values_mut() {
            for payload in payloads.iter_mut() {
                for listener in listeners.iter_mut() {
                    (listener)(world, payload.deref_mut())?;
                }
            }

            payloads.clear();
        }

        Ok(())
    }
}