1 files changed, 165 insertions, 3 deletions

diff --git a/ecs/src/uid.rs b/ecs/src/uid.rs
index c3ed85b..6c97649 100644
--- a/ecs/src/uid.rs
+++ b/ecs/src/uid.rs
@@ -1,23 +1,28 @@
-use std::fmt::{Debug, Formatter};
+use std::fmt::{Debug, Display, Formatter};
 use std::mem::transmute;
 use std::sync::atomic::{AtomicU32, Ordering};
 
+use crate::component::Component;
 use crate::util::{gen_mask_64, BitMask, NumberExt};
 
-static NEXT: AtomicU32 = AtomicU32::new(1);
+static NEXT: AtomicU32 = AtomicU32::new(Uid::FIRST_UNIQUE_ID);
+
+static WILDCARD_ID: u32 = 1;
 
 const ID_BITS: BitMask<u64> = BitMask::new(gen_mask_64!(32..=63));
+const RELATION_BITS: BitMask<u64> = BitMask::new(gen_mask_64!(6..=31));
 const KIND_BITS: BitMask<u64> = BitMask::new(gen_mask_64!(0..=1));
 
 #[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
 #[repr(u8)]
 pub enum Kind
 {
+    Pair = 3,
     Entity = 2,
     Component = 1,
 }
 
-/// Unique entity/component ID.
+/// A unique identifier.
 #[derive(Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Uid
 {
@@ -26,6 +31,10 @@ pub struct Uid
 
 impl Uid
 {
+    /// The id part of the first unique `Uid`. The ids `0..Uid::FIRST_UNIQUE_ID` are
+    /// reserved.
+    pub const FIRST_UNIQUE_ID: u32 = 5;
+
     /// Returns a new unique entity/component ID.
     pub fn new_unique(kind: Kind) -> Self
     {
@@ -37,6 +46,37 @@ impl Uid
     }
 
     #[must_use]
+    pub fn wildcard() -> Self
+    {
+        Self {
+            inner: ID_BITS.field_prep(u64::from(WILDCARD_ID))
+                | KIND_BITS.field_prep(Kind::Component as u64),
+        }
+    }
+
+    #[must_use]
+    pub fn new_pair(params: PairParams) -> Self
+    {
+        assert_ne!(
+            params.relation.kind(),
+            Kind::Pair,
+            "Pair relation cannot be a pair"
+        );
+
+        assert_ne!(
+            params.target.kind(),
+            Kind::Pair,
+            "Pair target cannot be a pair"
+        );
+
+        Self {
+            inner: ID_BITS.field_prep(u64::from(params.target.id()))
+                | RELATION_BITS.field_prep(u64::from(params.relation.id()))
+                | KIND_BITS.field_prep(Kind::Pair as u64),
+        }
+    }
+
+    #[must_use]
     pub fn id(&self) -> u32
     {
         let Ok(id) = u32::try_from(self.inner.field_get(ID_BITS)) else {
@@ -57,6 +97,76 @@ impl Uid
         // in the new_unique function
         unsafe { transmute::<u8, Kind>(kind) }
     }
+
+    /// If this `Uid` is a pair, returns the relation as a component `Uid`.
+    ///
+    /// # Panics
+    /// Will panic if this `Uid` is not a pair.
+    pub fn relation_component(&self) -> Self
+    {
+        assert_eq!(self.kind(), Kind::Pair, "Uid is not a pair");
+
+        Self {
+            inner: ID_BITS.field_prep(u64::from(self.relation()))
+                | KIND_BITS.field_prep(Kind::Component as u64),
+        }
+    }
+
+    pub fn has_same_relation_as(&self, other: Self) -> bool
+    {
+        self.relation() == other.relation()
+    }
+
+    /// If this `Uid` is a pair, returns the relation as a entity `Uid`.
+    ///
+    /// # Panics
+    /// Will panic if this `Uid` is not a pair.
+    pub fn relation_entity(&self) -> Self
+    {
+        assert_eq!(self.kind(), Kind::Pair, "Uid is not a pair");
+
+        Self {
+            inner: ID_BITS.field_prep(u64::from(self.relation()))
+                | KIND_BITS.field_prep(Kind::Entity as u64),
+        }
+    }
+
+    /// If this `Uid` is a pair, returns the target as a component `Uid`.
+    ///
+    /// # Panics
+    /// Will panic if this `Uid` is not a pair.
+    pub fn target_component(&self) -> Self
+    {
+        assert_eq!(self.kind(), Kind::Pair, "Uid is not a pair");
+
+        Self {
+            inner: ID_BITS.field_prep(u64::from(self.id()))
+                | KIND_BITS.field_prep(Kind::Component as u64),
+        }
+    }
+
+    /// If this `Uid` is a pair, returns the target as a entity `Uid`.
+    ///
+    /// # Panics
+    /// Will panic if this `Uid` is not a pair.
+    pub fn target_entity(&self) -> Self
+    {
+        assert_eq!(self.kind(), Kind::Pair, "Uid is not a pair");
+
+        Self {
+            inner: ID_BITS.field_prep(u64::from(self.id()))
+                | KIND_BITS.field_prep(Kind::Entity as u64),
+        }
+    }
+
+    fn relation(&self) -> u32
+    {
+        let Ok(relation) = u32::try_from(self.inner.field_get(RELATION_BITS)) else {
+            unreachable!("Uid relation does not fit in u32");
+        };
+
+        relation
+    }
 }
 
 impl Debug for Uid
@@ -70,3 +180,55 @@ impl Debug for Uid
             .finish_non_exhaustive()
     }
 }
+
+impl Display for Uid
+{
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> std::fmt::Result
+    {
+        if self.kind() == Kind::Pair {
+            return write!(
+                formatter,
+                "({}, {})",
+                self.relation(),
+                self.target_component()
+            );
+        }
+
+        if *self == Uid::wildcard() {
+            return write!(formatter, "*");
+        }
+
+        write!(formatter, "{}", self.id())
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct PairParams
+{
+    pub relation: Uid,
+    pub target: Uid,
+}
+
+pub trait With: 'static
+{
+    fn uid() -> Uid;
+}
+
+impl<ComponentT: Component> With for ComponentT
+{
+    fn uid() -> Uid
+    {
+        Self::id()
+    }
+}
+
+#[derive(Debug)]
+pub enum Wildcard {}
+
+impl With for Wildcard
+{
+    fn uid() -> Uid
+    {
+        Uid::wildcard()
+    }
+}