refactor: optimize code, fix bugs

src/merkle/partial_mt/mod.rs

@@ -22,6 +22,7 @@ const EMPTY_DIGEST: RpoDigest = RpoDigest::new(EMPTY_WORD);
 /// Tree allows to create Merkle Tree by providing Merkle paths of different lengths.
 ///
 /// The root of the tree is recomputed on each new leaf update.
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PartialMerkleTree {
     max_depth: u8,
     nodes: BTreeMap<NodeIndex, RpoDigest>,
@@ -112,12 +113,12 @@ impl PartialMerkleTree {
     /// Returns a vector of paths from every leaf to the root.
     pub fn paths(&self) -> Vec<(NodeIndex, ValuePath)> {
         let mut paths = Vec::new();
-        self.leaves.iter().for_each(|leaf| {
+        self.leaves.iter().for_each(|&leaf| {
             paths.push((
-                *leaf,
+                leaf,
                 ValuePath {
-                    value: *self.get_node(*leaf).expect("Failed to get leaf node"),
-                    path: self.get_path(*leaf).expect("Failed to get path"),
+                    value: *self.get_node(leaf).expect("Failed to get leaf node"),
+                    path: self.get_path(leaf).expect("Failed to get path"),
                 },
             ));
         });
@@ -160,10 +161,10 @@ impl PartialMerkleTree {
 
     /// Returns an iterator over the leaves of this [PartialMerkleTree].
     pub fn leaves(&self) -> impl Iterator<Item = (NodeIndex, RpoDigest)> + '_ {
-        self.leaves.iter().map(|leaf| {
+        self.leaves.iter().map(|&leaf| {
             (
-                *leaf,
-                self.get_node(*leaf).unwrap_or_else(|_| {
+                leaf,
+                self.get_node(leaf).unwrap_or_else(|_| {
                     panic!(
                         "Leaf with node index ({}, {}) is not in the nodes map",
                         leaf.depth(),
@@ -214,19 +215,25 @@ impl PartialMerkleTree {
             self.nodes.insert(index_value, node);
 
             // if the calculated node was a leaf, remove it from leaves set.
-            if self.leaves.contains(&index_value) {
-                self.leaves.remove(&index_value);
-            }
+            self.leaves.remove(&index_value);
 
             let sibling_node = index_value.sibling();
-            // node became a leaf only if it is a new node (it wasn't in nodes map)
-            if !self.nodes.contains_key(&sibling_node) {
+
+            // Insert node from Merkle path to the nodes map. This sibling node becomes a leaf only
+            // if it is a new node (it wasn't in nodes map).
+            // Node can be in 3 states: internal node, leaf of the tree and not a node at all.
+            // - Internal node can only stay in this state -- addition of a new path can't make it
+            // a leaf or remove it from the tree.
+            // - Leaf node can stay in the same state (remain a leaf) or can become an internal
+            // node. In the first case we don't need to do anything, and the second case is handled
+            // in the line 219.
+            // - New node can be a calculated node or a "sibling" node from a Merkle Path:
+            // --- Calculated node, obviously, never can be a leaf.
+            // --- Sibling node can be only a leaf, because otherwise it is not a new node.
+            if self.nodes.insert(sibling_node, hash.into()).is_none() {
                 self.leaves.insert(sibling_node);
             }
 
-            // insert node from Merkle path to the nodes map
-            self.nodes.insert(sibling_node, hash.into());
-
             Rpo256::merge(&index_value.build_node(node, hash.into()))
         });
 
@@ -238,8 +245,6 @@ impl PartialMerkleTree {
             return Err(MerkleError::ConflictingRoots([*self.root(), *root].to_vec()));
         }
 
-        // self.update_leaves()?;
-
         Ok(())
     }
 
@@ -250,7 +255,7 @@ impl PartialMerkleTree {
         &mut self,
         node_index: NodeIndex,
         value: RpoDigest,
-    ) -> Result<RpoDigest, MerkleError> {
+    ) -> Result<Option<RpoDigest>, MerkleError> {
         // check correctness of the depth and update it
         Self::check_depth(node_index.depth())?;
         self.update_depth(node_index.depth());
@@ -259,38 +264,19 @@ impl PartialMerkleTree {
         self.leaves.insert(node_index);
 
         // add node value to the nodes Map
-        let old_value = self.nodes.insert(node_index, value).unwrap_or(EMPTY_DIGEST);
+        let old_value = self.nodes.insert(node_index, value);
 
         // if the old value and new value are the same, there is nothing to update
-        if value == old_value {
-            return Ok(value);
+        if old_value.is_some() && value == old_value.unwrap() {
+            return Ok(old_value);
         }
 
         let mut node_index = node_index;
         let mut value = value;
         for _ in 0..node_index.depth() {
-            let is_right = node_index.is_value_odd();
-            let (left, right) = if is_right {
-                let left_index = NodeIndex::new(node_index.depth(), node_index.value() - 1)?;
-                (
-                    self.nodes
-                        .get(&left_index)
-                        .cloned()
-                        .ok_or(MerkleError::NodeNotInSet(left_index))?,
-                    value,
-                )
-            } else {
-                let right_index = NodeIndex::new(node_index.depth(), node_index.value() + 1)?;
-                (
-                    value,
-                    self.nodes
-                        .get(&right_index)
-                        .cloned()
-                        .ok_or(MerkleError::NodeNotInSet(right_index))?,
-                )
-            };
+            let sibling = self.nodes.get(&node_index.sibling()).expect("sibling should exist");
+            value = Rpo256::merge(&node_index.build_node(value, *sibling));
             node_index.move_up();
-            value = Rpo256::merge(&[left, right]);
             self.nodes.insert(node_index, value);
         }