From 4632dd8e9e95a377993ef677a157202fda8072f9 Mon Sep 17 00:00:00 2001
From: Dominik Kaiser
Date: Tue, 2 Jun 2026 23:23:57 +0200
Subject: Implement ECS

---
 src/sparse_set.rs | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 src/sparse_set.rs

(limited to 'src/sparse_set.rs')

diff --git a/src/sparse_set.rs b/src/sparse_set.rs
new file mode 100644
index 0000000..d7a69eb
--- /dev/null
+++ b/src/sparse_set.rs
@@ -0,0 +1,100 @@
+use super::Entity;
+
+pub struct SparseSet<T> {
+    pub dense: Vec<T>,
+    pub entities: Vec<Entity>,
+    pub sparse: Vec<Option<usize>>,
+}
+
+impl<T> SparseSet<T> {
+    pub fn new() -> Self {
+        Self {
+            dense: Vec::new(),
+            entities: Vec::new(),
+            sparse: Vec::new(),
+        }
+    }
+
+    pub fn insert(&mut self, entity: Entity, component: T) {
+        if self.sparse.len() <= entity {
+            self.sparse.resize(entity + 1, None);
+        }
+
+        self.dense.push(component);
+        self.entities.push(entity);
+
+        let id = self.dense.len() - 1;
+        self.sparse[entity] = Some(id);
+    }
+
+    pub fn remove(&mut self, entity: Entity) {
+        let Some(id) = self.sparse.get(entity).copied().flatten() else {
+            return;
+        };
+        let Some(last) = self.entities.last().copied() else {
+            return;
+        };
+        self.dense.swap_remove(id);
+        self.entities.swap_remove(id);
+        self.sparse[last] = Some(id);
+        self.sparse[entity] = None;
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = (Entity, &T)> {
+        self.entities.iter().copied().zip(self.dense.iter())
+    }
+
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = (Entity, &mut T)> {
+        self.entities.iter().copied().zip(self.dense.iter_mut())
+    }
+
+    pub fn get(&self, entity: Entity) -> Option<&T> {
+        if let Some(id) = self.sparse.get(entity) {
+            match id {
+                Some(id) => self.dense.get(*id),
+                None => None,
+            }
+        } else {
+            None
+        }
+    }
+
+    pub fn get_mut(&mut self, entity: Entity) -> Option<&mut T> {
+        if let Some(id) = self.sparse.get(entity) {
+            match id {
+                Some(id) => self.dense.get_mut(*id),
+                None => None,
+            }
+        } else {
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+
+    #[test]
+    fn test_remove() {
+        let mut set = SparseSet::<i32>::new();
+        set.insert(3, 300);
+        set.insert(2, 200);
+        set.insert(4, 400);
+        set.insert(7, 700);
+
+        set.remove(4);
+
+        assert!(set.get(7).copied() == Some(700));
+        assert!(set.get(3).copied() == Some(300));
+        assert!(set.get(2).copied() == Some(200));
+        assert!(set.get(4).copied().is_none());
+
+        set.remove(7);
+        assert!(set.get(7).copied().is_none());
+        assert!(set.get(3).copied() == Some(300));
+        assert!(set.get(2).copied() == Some(200));
+        assert!(set.get(4).copied().is_none());
+    }
+}
-- 
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