path: root/ecs/src/lib.rs

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

use std::any::{type_name, Any, TypeId};
use std::collections::{HashMap, HashSet};
use std::fmt::Debug;
use std::marker::PhantomData;
use std::mem::ManuallyDrop;
use std::ops::RangeBounds;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Weak};
use std::vec::Drain;

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

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

pub use ecs_macros::Component;

#[derive(Debug, Default)]
struct Entity
{
    components: Vec<ManuallyDrop<EntityComponent>>,
}

#[derive(Debug)]
struct EntityComponent
{
    id: TypeId,
    component: Lock<Box<dyn Component>>,
    drop_last: bool,
}

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

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

    /// Creates a new entity with the given components.
    ///
    /// # Panics
    /// Will panic if mutable internal lock cannot be acquired.
    pub fn create_entity<Comps>(&mut self, components: Comps)
    where
        Comps: ComponentSequence,
    {
        self.data
            .component_storage
            .write_nonblock()
            .expect("Failed to acquire read-write component storage lock")
            .entities
            .push(Entity {
                components: components
                    .into_vec()
                    .into_iter()
                    .map(|component| {
                        let drop_last = component.drop_last();

                        ManuallyDrop::new(EntityComponent {
                            id: (*component).type_id(),
                            component: Lock::new(component),
                            drop_last,
                        })
                    })
                    .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)
    {
        self.emit_event_by_id(event.id());
    }

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

    /// Peforms the actions that have been queued up using [`Actions`].
    ///
    /// # Panics
    /// Will panic if a mutable internal lock cannot be acquired.
    pub fn perform_queued_actions(&self)
    {
        for action in self
            .data
            .action_queue
            .write_nonblock()
            .expect("Failed to aquire read-write action queue lock")
            .drain(..)
        {
            match action {
                Action::Spawn(components) => {
                    self.data
                        .component_storage
                        .write_nonblock()
                        .expect("Failed to acquire read-write component storage lock")
                        .entities
                        .push(Entity {
                            components: components
                                .into_iter()
                                .map(|component| {
                                    let drop_last = component.drop_last();

                                    ManuallyDrop::new(EntityComponent {
                                        id: (*component).type_id(),
                                        component: Lock::new(component),
                                        drop_last,
                                    })
                                })
                                .collect(),
                        });
                }
                Action::Stop => {
                    self.stop.store(true, Ordering::Relaxed);
                }
            }
        }
    }

    /// A event loop which runs until a stop is issued with [`Flags::stop`].
    ///
    /// # Panics
    /// Will panic if a internal lock cannot be acquired.
    pub fn event_loop<EventSeq: EventSequence>(&self)
    {
        let event_seq = EventSeq::ids();

        loop {
            for event_id in event_seq.iter() {
                self.emit_event_by_id(*event_id);
            }

            self.perform_queued_actions();

            if self.stop.load(Ordering::Relaxed) {
                break;
            }
        }
    }

    fn emit_event_by_id(&self, event_id: EventId)
    {
        let Some(system_indices) = self.data.events.get(&event_id) 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);
            }
        }
    }
}

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

#[derive(Debug, Default)]
struct ActionQueue
{
    queue: Vec<Action>,
}

impl ActionQueue
{
    fn push(&mut self, action: Action)
    {
        self.queue.push(action);
    }

    fn drain(&mut self, range: impl RangeBounds<usize>) -> Drain<Action>
    {
        self.queue.drain(range)
    }
}

impl TypeName for ActionQueue
{
    fn type_name(&self) -> &'static str
    {
        type_name::<Self>()
    }
}

/// A entity query.
#[derive(Debug)]
pub struct Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    component_storage: ReadGuard<'world, ComponentStorage>,
    component_storage_lock: Weak<Lock<ComponentStorage>>,
    comps_pd: PhantomData<Comps>,
}

impl<'world, Comps> Query<'world, Comps>
where
    Comps: ComponentSequence,
{
    #[must_use]
    pub fn iter<'this>(&'this self) -> QueryComponentIter<'world, Comps>
    where
        'this: 'world,
    {
        QueryComponentIter {
            component_storage: &self.component_storage,
            current_entity_index: 0,
            component_type_ids: Comps::type_ids(),
            comps_pd: PhantomData,
        }
    }

    /// Returns a weak reference query to the same components.
    #[must_use]
    pub fn to_weak_ref(&self) -> WeakRefQuery<Comps>
    {
        WeakRefQuery {
            component_storage: self.component_storage_lock.clone(),
            comps_pd: PhantomData,
        }
    }

    fn new(component_storage: &'world Arc<Lock<ComponentStorage>>) -> Self
    {
        Self {
            component_storage: component_storage
                .read_nonblock()
                .expect("Failed to acquire read-only component storage lock"),
            component_storage_lock: Arc::downgrade(component_storage),
            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.component_storage)
    }

    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(),
        })
    }
}

/// A entity query containing a weak reference to the world.
#[derive(Debug)]
pub struct WeakRefQuery<Comps>
where
    Comps: ComponentSequence,
{
    component_storage: Weak<Lock<ComponentStorage>>,
    comps_pd: PhantomData<Comps>,
}

impl<Comps> WeakRefQuery<Comps>
where
    Comps: ComponentSequence,
{
    /// Returns a struct which can be used to retrieve a [`Query`].
    ///
    /// Returns [`None`] if the [`World`] has been dropped.
    #[must_use]
    pub fn access(&self) -> Option<RefQuery<'_, Comps>>
    {
        Some(RefQuery {
            component_storage: self.component_storage.upgrade()?,
            _pd: PhantomData,
        })
    }
}

impl<Comps> Clone for WeakRefQuery<Comps>
where
    Comps: ComponentSequence,
{
    fn clone(&self) -> Self
    {
        Self {
            component_storage: self.component_storage.clone(),
            comps_pd: PhantomData,
        }
    }
}

/// Intermediate between [`Query`] and [`WeakRefQuery`]. Contains a strong reference to
/// the world which is not allowed direct access to.
#[derive(Debug, Clone)]
pub struct RefQuery<'weak_ref, Comps>
where
    Comps: ComponentSequence,
{
    component_storage: Arc<Lock<ComponentStorage>>,
    _pd: PhantomData<&'weak_ref Comps>,
}

impl<'weak_ref, Comps> RefQuery<'weak_ref, Comps>
where
    Comps: ComponentSequence,
{
    #[must_use]
    pub fn to_query(&self) -> Query<'_, Comps>
    {
        Query::new(&self.component_storage)
    }
}

#[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>
{
    component_storage: &'world ComponentStorage,
    current_entity_index: usize,
    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_index, matching_entity) =
            self.component_storage.find_entity_with_components(
                self.current_entity_index,
                &self.component_type_ids,
            )?;

        self.current_entity_index = matching_entity_index + 1;

        Some(Comps::from_components(
            matching_entity
                .components
                .iter()
                .map(|component| &component.component),
        ))
    }
}

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

impl ComponentStorage
{
    fn find_entity_with_components(
        &self,
        start_index: usize,
        component_type_ids: &[TypeId],
    ) -> Option<(usize, &Entity)>
    {
        // TODO: This is a really dumb and slow way to do this. Refactor the world
        // to store components in archetypes
        self.entities.iter().enumerate().skip(start_index).find(
            move |(_index, entity)| {
                let entity_components = entity
                    .components
                    .iter()
                    .map(|component| component.id)
                    .collect::<HashSet<_>>();

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

                false
            },
        )
    }
}

impl TypeName for ComponentStorage
{
    fn type_name(&self) -> &'static str
    {
        type_name::<Self>()
    }
}

impl Drop for ComponentStorage
{
    fn drop(&mut self)
    {
        let mut components_to_drop_last = Vec::new();

        for entity in &mut self.entities {
            for component in &mut entity.components {
                if component.drop_last {
                    #[cfg(feature = "debug")]
                    tracing::debug!(
                        "Component {} pushed to dropping last queue",
                        component.component.read_nonblock().unwrap().type_name()
                    );

                    components_to_drop_last.push(component);
                    continue;
                }

                #[cfg(feature = "debug")]
                tracing::debug!(
                    "Dropping component {}",
                    component.component.read_nonblock().unwrap().type_name()
                );

                unsafe {
                    ManuallyDrop::drop(component);
                }
            }
        }

        for component in &mut components_to_drop_last {
            #[cfg(feature = "debug")]
            tracing::debug!(
                "Dropping component {} last",
                component.component.read_nonblock().unwrap().type_name()
            );

            unsafe {
                ManuallyDrop::drop(component);
            }
        }
    }
}