1 files changed, 90 insertions, 0 deletions
diff --git a/src/ctx.rs b/src/ctx.rs
new file mode 100644
index 0000000..38aa4ae
--- /dev/null
+++ b/src/ctx.rs
@@ -0,0 +1,90 @@
+use crate::quad::{Quad, Node};
+
+/// Represents a context with shared state.
+pub struct Ctx();
+
+impl Ctx {
+    /// Creates a new uninitialized context.
+    pub fn new_empty() -> Self {
+        Ctx()
+    }
+
+    /// Combines 4 child node representations into a single representation
+    /// Using a neural network.
+    pub fn combine<B>(&mut self, compr: [B; 4]) -> B {
+        todo!("Build new B from 4 child B");
+    }
+
+    /// Compresses a base-level cell into a vector.
+    pub fn compress_base<A, B>(&mut self, base: A) -> B {
+        todo!("Turn Base Cell into a vector B");
+    }
+
+    /// Compresses a single node into a vector representation.
+    /// Returns `None` if node has already been compressed and trimmed from tree.
+    /// To recover a trimmed node, use `expand` on the compressed representation.
+    pub fn compress<A: Default, B: Copy>(&mut self, quad: &Quad<A, B>) -> Option<B> {
+        match quad {
+            Quad::Base(b) => Some(self.compress_base(b)),
+            Quad::Node(n) => Some(
+                self.combine([
+                    n[0].compr,
+                    n[1].compr,
+                    n[2].compr,
+                    n[3].compr,
+                ])
+            ),
+            Quad::Cached => None,
+        }
+    }
+
+    /// Compresses a base-level cell into a vector.
+    fn expand_base<A: Default, B: Copy>(&mut self, compr: B) -> A {
+        todo!("Turn compressed B into the A that made it");
+    }
+
+    fn expand_node<B>(&mut self, compr: B) -> [B; 4] {
+        todo!("Turn compressed B into 4 child B that made it");
+    }
+
+    /// Expands the compressed representation of a node into a node with 4 children.
+    pub fn expand<A: Default, B: Copy>(&mut self, mut compr: Node<A, B>) -> Node<A, B> {
+        match compr.data {
+            // Can't expand a base node.
+            Quad::Base(_) => {
+                debug_assert!(compr.depth == 0, "Tree is malformed at the leaves");
+                compr
+            },
+
+            // No-op if node is already expanded.
+            Quad::Node(_) => {
+                debug_assert!(compr.depth != 0, "Tree is malformed along the trunk");
+                compr
+            },
+
+            Quad::Cached => {
+                // Expand and repace the current node data.
+                compr.data = if compr.depth == 0 {
+                    // Base case.
+                    Quad::Base(self.expand_base(compr.compr))
+                } else {
+                    // Expand the children into their corresponding vectors.
+                    let c = self.expand_node(compr.compr);
+                    // Pack the children into a new Node.
+                    let new_depth = compr.depth - 1;
+                    let children = [
+                        Node::new_cached(c[0], new_depth),
+                        Node::new_cached(c[1], new_depth),
+                        Node::new_cached(c[2], new_depth),
+                        Node::new_cached(c[3], new_depth),
+                    ];
+                    // Heap-allocate the node lol.
+                    Quad::Node(Box::new(children))
+                };
+
+                // The updated node.
+                compr
+            },
+        }
+    }
+}