lyra-engine/lyra-ecs/src/world.rs

use std::collections::{HashMap, VecDeque};

use crate::{archetype::{ArchetypeId, Archetype}, bundle::Bundle, component::Component, query::{ViewIter, View, DefaultQuery}};

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct EntityId(pub u64);

/// The id of the entity for the Archetype.
/// The Archetype struct uses this as the index in the component columns
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct ArchetypeEntityId(pub u64);

#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct Entity {
    id: EntityId,
    generation: u64,
}

pub struct Record {
    id: ArchetypeId,
    index: ArchetypeEntityId,
}

pub struct World {
    pub(crate) archetypes: HashMap<ArchetypeId, Archetype>,
    next_archetype_id: ArchetypeId,
    entity_index: HashMap<EntityId, Record>,
    dead_entities: VecDeque<Entity>,
    next_entity_id: EntityId,
}

impl World {
    pub fn new() -> Self {
        Self {
            archetypes: HashMap::new(),
            next_archetype_id: ArchetypeId(0),
            entity_index: HashMap::new(),
            dead_entities: VecDeque::new(),
            next_entity_id: EntityId(0),
        }
    }

    fn get_new_entity(&mut self) -> Entity {
        match self.dead_entities.pop_front() {
            Some(e) => e,
            None => {
                let new_id = self.next_entity_id;
                self.next_entity_id.0 += 1;

                Entity {
                    id: new_id,
                    generation: 0,
                }
            }
        }
    }

    pub fn spawn<B>(&mut self, bundle: B) -> Entity
    where
        B: Bundle
    {
        let bundle_types = bundle.type_ids();
        let new_entity = self.get_new_entity();

        // try to find an archetype
        let archetype = self.archetypes
            .values_mut()
            .find(|a| a.is_archetype_for(bundle_types.clone()));

        if let Some(archetype) = archetype {
            let arche_idx = archetype.add_entity(new_entity, bundle);

            // Create entity record and store it
            let record = Record {
                id: archetype.id,
                index: arche_idx,
            };
            
            self.entity_index.insert(new_entity.id, record);
        }
        // create a new archetype if one isn't found
        else {
            // create archetype
            let new_arch_id = self.next_archetype_id.increment();
            let mut archetype = Archetype::from_bundle_info(new_arch_id, bundle.info());
            let entity_arch_id = archetype.add_entity(new_entity, bundle);

            // store archetype
            self.archetypes.insert(new_arch_id, archetype);

            // Create entity record and store it
            let record = Record {
                id: new_arch_id,
                // this is the first entity in the archetype
                index: entity_arch_id,
            };

            self.entity_index.insert(new_entity.id, record);
        }
        
        new_entity
    }

    pub fn view<'a, T: 'static + Component + DefaultQuery>(&'a self) -> ViewIter<'a, T::Query> {
        let archetypes = self.archetypes.values().collect();
        let v = View::new(T::default_query(), archetypes);
        v.into_iter()
    }
}

#[cfg(test)]
mod tests {
    use crate::tests::Vec2;

    use super::World;

    #[test]
    fn spawning_entity() {
        let mut world = World::new();
        let _e = world.spawn((Vec2 {
            x: 10.0,
            y: 15.0,
        }, ));
    }

    #[test]
    fn world_view_entities() {
        let mut world = World::new();
        world.spawn((Vec2 {
            x: 10.0,
            y: 15.0,
        }, ));
        world.spawn((Vec2 {
            x: 152.0,
            y: 3585.0,
        }, ));
        world.spawn((Vec2 {
            x: 235.0,
            y: 734.0,
        }, ));

        let mut count = 0;
        for pos in world.view::<&Vec2>() {
            println!("Found entity at {:?}", pos);
            count += 1;
        }
        assert!(count == 3);
    }
}