path: root/ecs/src/lib.rs

#![deny(clippy::all, clippy::pedantic)]

use std::any::{Any, TypeId};
use std::cell::RefCell;
use std::collections::{HashMap, HashSet};
use std::fmt::Debug;
use std::marker::PhantomData;
use std::slice::Iter as SliceIter;

use crate::actions::Action;
use crate::component::{Component, Sequence as ComponentSequence};
use crate::event::{Event, Id as EventId};
use crate::system::{
    NoInitParamFlag as NoInitSystemParamFlag,
    Param as SystemParam,
    System,
    TypeErased as TypeErasedSystem,
};
use crate::tuple::FilterExclude as TupleFilterExclude;

pub mod actions;
pub mod component;
pub mod event;
pub mod system;
pub mod tuple;

pub use ecs_macros::Component;

#[derive(Debug, Default)]
struct Entity
{
    components: Vec<RefCell<Box<dyn Component>>>,
}

#[derive(Debug, Default)]
pub struct World
{
    systems: Vec<TypeErasedSystem>,
    data: WorldData,
}

impl World
{
    #[must_use]
    pub fn new() -> Self
    {
        Self::default()
    }

    pub fn create_entity<Comps>(&mut self, components: Comps)
    where
        Comps: ComponentSequence,
    {
        self.data.component_storage.entities.push(Entity {
            components: components
                .into_vec()
                .into_iter()
                .map(RefCell::new)
                .collect(),
        });
    }

    pub fn register_system<'this, SystemImpl>(
        &'this mut self,
        event: &impl Event,
        system: impl System<'this, SystemImpl>,
    )
    {
        self.systems.push(system.into_type_erased());

        self.data
            .events
            .entry(event.id())
            .or_default()
            .push(self.systems.len() - 1);
    }

    /// Emits a event, running all systems listening to the event for each compatible
    /// entity.
    ///
    /// # Panics
    /// Will panic if a system has dissapeared.
    pub fn emit(&self, event: &impl Event)
    {
        let Some(system_indices) = self.data.events.get(&event.id()).cloned() else {
            return;
        };

        for system_index in system_indices {
            let system = self.systems.get(system_index).unwrap();

            // SAFETY: The world data lives long enough
            unsafe {
                system.run(&self.data);
            }
        }
    }

    pub fn query<Comps>(&self) -> Query<Comps>
    where
        Comps: ComponentSequence,
    {
        Query::new(&self.data)
    }

    /// Peforms the actions that have been queued up using [`Actions`].
    pub fn perform_queued_actions(&mut self)
    {
        for action in self.data.action_queue.borrow_mut().drain(..) {
            match action {
                Action::Spawn(components) => {
                    self.data.component_storage.entities.push(Entity {
                        components: components.into_iter().map(RefCell::new).collect(),
                    });
                }
            }
        }
    }
}

#[derive(Debug, Default)]
pub struct WorldData
{
    events: HashMap<EventId, Vec<usize>>,
    component_storage: ComponentStorage,
    action_queue: RefCell<Vec<Action>>,
}

#[derive(Debug)]
pub struct Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    world_data: &'world WorldData,
    comps_pd: PhantomData<Comps>,
}

impl<'world, Comps> Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    pub fn iter(&self) -> QueryComponentIter<'world, Comps>
    {
        QueryComponentIter {
            entity_iter: self.world_data.component_storage.entities.iter(),
            component_type_ids: Comps::type_ids(),
            comps_pd: PhantomData,
        }
    }

    fn new(world_data: &'world WorldData) -> Self
    {
        Self { world_data, comps_pd: PhantomData }
    }
}

impl<'world, Comps> IntoIterator for &'world Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    type IntoIter = QueryComponentIter<'world, Comps>;
    type Item = Comps::Refs<'world>;

    fn into_iter(self) -> Self::IntoIter
    {
        self.iter()
    }
}

unsafe impl<'world, Comps> SystemParam<'world> for Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    type Flags = NoInitSystemParamFlag;
    type Input = TupleFilterExclude;

    fn initialize<SystemImpl>(
        _system: &mut impl System<'world, SystemImpl>,
        _input: Self::Input,
    )
    {
    }

    fn new<SystemImpl>(
        _system: &'world impl System<'world, SystemImpl>,
        world_data: &'world WorldData,
    ) -> Self
    {
        Self::new(world_data)
    }

    fn is_compatible<Other: SystemParam<'world>>() -> bool
    {
        let other_comparable = Other::get_comparable();

        let Some(other_query_component_ids) =
            other_comparable.downcast_ref::<QueryComponentIds>()
        else {
            return true;
        };

        !other_query_component_ids.contains_component_in::<Comps>()
    }

    fn get_comparable() -> Box<dyn Any>
    {
        Box::new(QueryComponentIds {
            component_type_ids: Comps::type_ids(),
        })
    }
}

#[derive(Debug)]
struct QueryComponentIds
{
    component_type_ids: Vec<TypeId>,
}

impl QueryComponentIds
{
    fn contains_component_in<OtherComps>(&self) -> bool
    where
        OtherComps: ComponentSequence,
    {
        let other_component_type_ids = OtherComps::type_ids()
            .into_iter()
            .collect::<HashSet<TypeId>>();

        // TODO: Make this a bit smarter. Queries with a same component can be compatible
        // if one of the queries have a component the other one does not have
        self.component_type_ids
            .iter()
            .any(|component_type_id| other_component_type_ids.contains(component_type_id))
    }
}

pub struct QueryComponentIter<'world, Comps>
{
    entity_iter: SliceIter<'world, Entity>,
    component_type_ids: Vec<TypeId>,
    comps_pd: PhantomData<Comps>,
}

impl<'world, Comps> Iterator for QueryComponentIter<'world, Comps>
where
    Comps: ComponentSequence + 'world,
{
    type Item = Comps::Refs<'world>;

    fn next(&mut self) -> Option<Self::Item>
    {
        let matching_entity =
            find_entity_with_components(&mut self.entity_iter, &self.component_type_ids)?;

        Some(Comps::from_components(&matching_entity.components))
    }
}

fn find_entity_with_components<'world>(
    entity_iter: &mut impl Iterator<Item = &'world Entity>,
    component_type_ids: &[TypeId],
) -> Option<&'world Entity>
{
    // TODO: This is a really dumb and slow way to do this. Refactor the world
    // to store components in archetypes
    entity_iter.find(|entity| {
        let entity_components = entity
            .components
            .iter()
            .filter_map(|component| Some(component.try_borrow().ok()?.as_ref().type_id()))
            .collect::<HashSet<_>>();

        if component_type_ids
            .iter()
            .all(|component_type_id| entity_components.contains(component_type_id))
        {
            return true;
        }

        false
    })
}

#[derive(Debug, Default)]
pub struct ComponentStorage
{
    entities: Vec<Entity>,
}