chore: implement new function for Merkle Tree

src/lib.rs

@@ -1,5 +1,10 @@
 //! # pmtree
 //! Persistent Merkle Tree in Rust
+//!
+//! ## How it stored
+//! { [0, 0, ..., 0] : depth }
+//! { [0, 0, ..., 1] : next_index}
+//! { Position (tuple, converted to DBKey) : Value}
 
 pub mod database;
 pub mod hasher;
@@ -17,7 +22,7 @@ pub struct Error(String);
 pub type Result<T> = std::result::Result<T, Error>;
 
 /// Denotes keys in a database
-pub type DBKey = [u8; 32];
+pub type DBKey = [u8; 8];
 
 /// Denotes values in a database
 pub type Value = Vec<u8>;

src/tree.rs

@@ -1,5 +1,20 @@
 use crate::*;
 
+// db[DEPTH_KEY] = depth
+const DEPTH_KEY: DBKey = [0; 8];
+
+// db[NEXT_INDEX_KEY] = next_index;
+const NEXT_INDEX_KEY: DBKey = [1; 8];
+
+// Denotes keys (depth, index) in Merkle Tree. Can be converted to DBKey
+struct Key(usize, usize);
+impl From<Key> for DBKey {
+    fn from(key: Key) -> DBKey {
+        let cantor_pairing = (key.0 + key.1) * (key.0 + key.1 + 1) / 2 + key.1;
+        cantor_pairing.to_be_bytes()
+    }
+}
+
 /// Merkle Tree implementation
 pub struct MerkleTree<D, H>
 where
@@ -19,7 +34,32 @@ where
 {
     /// Creates new `MerkleTree` and store it to the specified path/db
     pub fn new(depth: usize, dbpath: &str) -> Result<Self> {
-        todo!()
+        // Create new db instance
+        let mut db = D::new(dbpath);
+
+        // Insert depth val into db
+        let depth_val = depth.to_be_bytes().to_vec();
+        db.put(DEPTH_KEY, depth_val)?;
+
+        // Insert next_index val into db
+        let next_index = 0usize;
+        let next_index_val = next_index.to_be_bytes().to_vec();
+        db.put(NEXT_INDEX_KEY, next_index_val)?;
+
+        // Initialize one branch of the `Merkle Tree` from bottom to top
+        let mut prev = H::default_leaf();
+        db.put(Key(depth, 0).into(), prev.into())?;
+        for i in (0..depth).rev() {
+            prev = H::hash(&[prev, prev]);
+            db.put(Key(i + 1, 0).into(), prev.into())?;
+        }
+
+        Ok(Self {
+            db,
+            h: H::new(),
+            depth,
+            next_index,
+        })
     }
 
     /// Loads existing Merkle Tree from the specified path/db
@@ -28,7 +68,7 @@ where
     }
 
     /// Inserts a leaf to the next available index
-    pub fn insert(&mut self, leaf: H::Fr) {
+    pub fn insert(&mut self, leaf: H::Fr) -> Result<()> {
         todo!()
     }
 
@@ -38,7 +78,7 @@ where
     }
 
     /// Deletes a  leaf at the `key` by setting it to its default value
-    pub fn delete(&mut self, key: usize) {
+    pub fn delete(&mut self, key: usize) -> Result<()> {
         todo!()
     }