1 files changed, 238 insertions, 0 deletions
diff --git a/ecs/src/query.rs b/ecs/src/query.rs
new file mode 100644
index 0000000..9874b19
--- /dev/null
+++ b/ecs/src/query.rs
@@ -0,0 +1,238 @@
+use std::any::{Any, TypeId};
+use std::collections::HashSet;
+use std::marker::PhantomData;
+use std::sync::{Arc, Weak};
+
+use crate::component::Sequence as ComponentSequence;
+use crate::lock::{Lock, ReadGuard};
+use crate::system::{
+    NoInitParamFlag as NoInitSystemParamFlag,
+    Param as SystemParam,
+    System,
+};
+use crate::tuple::FilterExclude as TupleFilterExclude;
+use crate::{ComponentStorage, WorldData};
+
+#[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) -> ComponentIter<'world, Comps>
+    where
+        'this: 'world,
+    {
+        ComponentIter {
+            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) -> WeakRef<Comps>
+    {
+        WeakRef {
+            component_storage: self.component_storage_lock.clone(),
+            comps_pd: PhantomData,
+        }
+    }
+
+    pub(crate) 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 = ComponentIter<'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 WeakRef<Comps>
+where
+    Comps: ComponentSequence,
+{
+    component_storage: Weak<Lock<ComponentStorage>>,
+    comps_pd: PhantomData<Comps>,
+}
+
+impl<Comps> WeakRef<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<Ref<'_, Comps>>
+    {
+        Some(Ref {
+            component_storage: self.component_storage.upgrade()?,
+            _pd: PhantomData,
+        })
+    }
+}
+
+impl<Comps> Clone for WeakRef<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 Ref<'weak_ref, Comps>
+where
+    Comps: ComponentSequence,
+{
+    component_storage: Arc<Lock<ComponentStorage>>,
+    _pd: PhantomData<&'weak_ref Comps>,
+}
+
+impl<'weak_ref, Comps> Ref<'weak_ref, Comps>
+where
+    Comps: ComponentSequence,
+{
+    #[must_use]
+    pub fn to_query(&self) -> Query<'_, Comps>
+    {
+        Query::new(&self.component_storage)
+    }
+}
+
+pub struct ComponentIter<'world, Comps>
+{
+    component_storage: &'world ComponentStorage,
+    current_entity_index: usize,
+    component_type_ids: Vec<TypeId>,
+    comps_pd: PhantomData<Comps>,
+}
+
+impl<'world, Comps> Iterator for ComponentIter<'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)]
+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))
+    }
+}