1 files changed, 201 insertions, 0 deletions
diff --git a/ecs/src/pair.rs b/ecs/src/pair.rs
new file mode 100644
index 0000000..27e535e
--- /dev/null
+++ b/ecs/src/pair.rs
@@ -0,0 +1,201 @@
+use std::convert::Infallible;
+
+use crate::component::storage::Storage as ComponentStorage;
+use crate::component::{IntoParts as IntoComponentParts, Parts as ComponentParts};
+use crate::entity::{
+    Handle as EntityHandle,
+    MatchingComponentIter as EntityMatchingComponentIter,
+};
+use crate::lock::ReadGuard;
+use crate::query::{
+    TermWithField as QueryTermWithField,
+    TermsBuilder as QueryTermsBuilder,
+    TermsBuilderInterface,
+};
+use crate::uid::{PairParams as UidPairParams, Uid, Wildcard, With as WithUid};
+use crate::{Component, World};
+
+#[derive(Debug)]
+pub struct Pair<RelationElem: Element, TargetElem: Element>
+{
+    relation: RelationElem,
+    target: TargetElem,
+}
+
+impl Pair<Uid, Uid>
+{
+    pub fn new<Relation: WithUid>(target: Uid) -> Self
+    {
+        Self { relation: Relation::uid(), target }
+    }
+
+    pub fn id(&self) -> Uid
+    {
+        Uid::new_pair(UidPairParams {
+            relation: self.relation,
+            target: self.target,
+        })
+    }
+}
+
+impl IntoComponentParts for Pair<Uid, Uid>
+{
+    fn into_parts(self) -> ComponentParts
+    {
+        ComponentParts::builder().name("Pair").build(self.id(), ())
+    }
+}
+
+impl<Relation, Target> QueryTermWithField for Pair<Relation, Target>
+where
+    Relation: WithUid,
+    Target: WithUid,
+{
+    type Field<'a> = Handle<'a>;
+
+    fn apply_to_terms_builder<const MAX_TERM_CNT: usize>(
+        terms_builder: &mut QueryTermsBuilder<MAX_TERM_CNT>,
+    )
+    {
+        terms_builder.with_required([Self::uid()]);
+    }
+
+    fn get_field<'world>(
+        entity_handle: &EntityHandle<'world>,
+        world: &'world World,
+    ) -> Self::Field<'world>
+    {
+        let first_matching_comp = entity_handle
+            .get_matching_components(Self::uid())
+            .next()
+            .expect("Not possible");
+
+        Handle {
+            world,
+            component_storage_lock: world.data.component_storage.read_nonblock().unwrap(),
+            pair_uid: first_matching_comp.id(),
+        }
+    }
+}
+
+impl<Relation, Target> WithUid for Pair<Relation, Target>
+where
+    Relation: WithUid,
+    Target: WithUid,
+{
+    fn uid() -> Uid
+    {
+        Uid::new_pair(UidPairParams {
+            relation: Relation::uid(),
+            target: Target::uid(),
+        })
+    }
+}
+
+impl<Relation> QueryTermWithField for &'static [Pair<Relation, Wildcard>]
+where
+    Relation: WithUid,
+{
+    type Field<'a> = HandleIter<'a>;
+
+    fn apply_to_terms_builder<const MAX_TERM_CNT: usize>(
+        terms_builder: &mut QueryTermsBuilder<MAX_TERM_CNT>,
+    )
+    {
+        terms_builder.with_required([Pair::<Relation, Wildcard>::uid()]);
+    }
+
+    fn get_field<'world>(
+        entity_handle: &EntityHandle<'world>,
+        world: &'world World,
+    ) -> Self::Field<'world>
+    {
+        HandleIter {
+            inner: entity_handle
+                .get_matching_components(Pair::<Relation, Wildcard>::uid()),
+            world,
+        }
+    }
+}
+
+pub struct Handle<'world>
+{
+    world: &'world World,
+    component_storage_lock: ReadGuard<'world, ComponentStorage>,
+    pair_uid: Uid,
+}
+
+impl Handle<'_>
+{
+    pub fn get_target_entity(&self) -> Option<EntityHandle<'_>>
+    {
+        let archetype = self
+            .component_storage_lock
+            .get_entity_archetype(self.pair_uid.target_entity())?;
+
+        let archetype_entity = archetype
+            .get_entity_by_id(self.pair_uid.target_entity())
+            .expect("Not possible");
+
+        Some(EntityHandle::new(self.world, archetype, archetype_entity))
+    }
+}
+
+pub struct HandleIter<'a>
+{
+    inner: EntityMatchingComponentIter<'a>,
+    world: &'a World,
+}
+
+impl<'a> Iterator for HandleIter<'a>
+{
+    type Item = Handle<'a>;
+
+    fn next(&mut self) -> Option<Self::Item>
+    {
+        let matching_comp = self.inner.next()?;
+
+        Some(Handle {
+            world: self.world,
+            component_storage_lock: self
+                .world
+                .data
+                .component_storage
+                .read_nonblock()
+                .unwrap(),
+            pair_uid: matching_comp.id(),
+        })
+    }
+}
+
+pub trait Element: sealed::Sealed
+{
+    type Value;
+}
+
+impl Element for Uid
+{
+    type Value = Uid;
+}
+
+impl sealed::Sealed for Uid {}
+
+impl<WithUidT: WithUid> Element for WithUidT
+{
+    type Value = Infallible;
+}
+
+impl<WithUidT: WithUid> sealed::Sealed for WithUidT {}
+
+/// Relation denoting a dependency to another entity
+#[derive(Debug, Default, Clone, Copy, Component)]
+pub struct DependsOn;
+
+/// Relation denoting being the child of another entity.
+#[derive(Debug, Default, Clone, Copy, Component)]
+pub struct ChildOf;
+
+mod sealed
+{
+    pub trait Sealed {}
+}