1 files changed, 84 insertions, 0 deletions
diff --git a/ecs/src/query/flexible.rs b/ecs/src/query/flexible.rs
new file mode 100644
index 0000000..add30b0
--- /dev/null
+++ b/ecs/src/query/flexible.rs
@@ -0,0 +1,84 @@
+//! Low-level querying.
+use std::iter::{repeat_n, FlatMap, RepeatN, Zip};
+
+use crate::component::storage::archetype::{Archetype, EntityIter};
+use crate::component::storage::{ArchetypeRefIter, ArchetypeSearchTerms};
+use crate::entity::Handle as EntityHandle;
+use crate::query::Terms;
+use crate::World;
+
+/// Low-level entity query structure.
+#[derive(Debug)]
+pub struct Query<'world, const MAX_TERM_CNT: usize>
+{
+    world: &'world World,
+    terms: Terms<MAX_TERM_CNT>,
+}
+
+impl<'world, const MAX_TERM_CNT: usize> Query<'world, MAX_TERM_CNT>
+{
+    /// Iterates over the entities matching this query.
+    #[must_use]
+    pub fn iter(&self) -> Iter<'_>
+    {
+        Iter {
+            iter: self
+                .world
+                .data
+                .component_storage
+                .search_archetypes(ArchetypeSearchTerms {
+                    required_components: &self.terms.required_components,
+                    excluded_components: &self.terms.excluded_components,
+                })
+                .flat_map(
+                    (|archetype| {
+                        repeat_n(archetype, archetype.entity_cnt())
+                            .zip(archetype.entities())
+                    }) as ComponentIterMapFn,
+                ),
+        }
+    }
+
+    pub(crate) fn new(world: &'world World, terms: Terms<MAX_TERM_CNT>) -> Self
+    {
+        Self { world, terms }
+    }
+}
+
+impl<'query, const MAX_TERM_CNT: usize> IntoIterator for &'query Query<'_, MAX_TERM_CNT>
+{
+    type IntoIter = Iter<'query>;
+    type Item = EntityHandle<'query>;
+
+    fn into_iter(self) -> Self::IntoIter
+    {
+        self.iter()
+    }
+}
+
+pub struct Iter<'query>
+{
+    iter: QueryEntityIter<'query>,
+}
+
+impl<'query> Iterator for Iter<'query>
+{
+    type Item = EntityHandle<'query>;
+
+    fn next(&mut self) -> Option<Self::Item>
+    {
+        let (archetype, entity) = self.iter.next()?;
+
+        Some(EntityHandle::new(archetype, entity))
+    }
+}
+
+type ComponentIterMapFnOutput<'a> = Zip<RepeatN<&'a Archetype>, EntityIter<'a>>;
+
+type ComponentIterMapFn = for<'a> fn(&'a Archetype) -> ComponentIterMapFnOutput<'a>;
+
+type QueryEntityIter<'query> = FlatMap<
+    ArchetypeRefIter<'query, 'query>,
+    ComponentIterMapFnOutput<'query>,
+    ComponentIterMapFn,
+>;