Allow for building cached vec

eth2/utils/ssz/src/cached_tree_hash/impls.rs

@@ -4,6 +4,10 @@ use crate::{ssz_encode, Encodable};
 impl CachedTreeHash for u64 {
     type Item = Self;
 
+    fn item_type() -> ItemType {
+        ItemType::Basic
+    }
+
     fn build_tree_hash_cache(&self) -> Result<TreeHashCache, Error> {
         Ok(TreeHashCache::from_bytes(merkleize(ssz_encode(self)))?)
     }
@@ -20,6 +24,10 @@ impl CachedTreeHash for u64 {
         0
     }
 
+    fn packed_encoding(&self) -> Vec<u8> {
+        ssz_encode(self)
+    }
+
     fn cached_hash_tree_root(
         &self,
         other: &Self,
@@ -35,38 +43,73 @@ impl CachedTreeHash for u64 {
     }
 }
 
-/*
 impl<T> CachedTreeHash for Vec<T>
 where
-    T: CachedTreeHash + Encodable,
+    T: CachedTreeHash,
 {
     type Item = Self;
 
-    fn build_cache_bytes(&self) -> Vec<u8> {
-        let num_packed_bytes = self.num_bytes();
-        let num_leaves = num_sanitized_leaves(num_packed_bytes);
+    fn item_type() -> ItemType {
+        ItemType::List
+    }
 
-        let mut packed = Vec::with_capacity(num_leaves * HASHSIZE);
+    fn build_tree_hash_cache(&self) -> Result<TreeHashCache, Error> {
+        match T::item_type() {
+            ItemType::Basic => {
+                let num_packed_bytes = self.num_bytes();
+                let num_leaves = num_sanitized_leaves(num_packed_bytes);
+
+                let mut packed = Vec::with_capacity(num_leaves * HASHSIZE);
+
+                for item in self {
+                    packed.append(&mut item.packed_encoding());
+                }
+
+                let packed = sanitise_bytes(packed);
+
+                TreeHashCache::from_bytes(merkleize(packed))
+            }
+            ItemType::Composite | ItemType::List => {
+                let subtrees = self
+                    .iter()
+                    .map(|item| TreeHashCache::new(item))
+                    .collect::<Result<Vec<TreeHashCache>, _>>()?;
+
+                TreeHashCache::from_leaves_and_subtrees(self, subtrees)
+            }
+        }
+    }
+
+    fn offsets(&self) -> Result<Vec<usize>, Error> {
+        let mut offsets = vec![];
 
         for item in self {
-            packed.append(&mut ssz_encode(item));
+            offsets.push(item.offsets()?.iter().sum())
         }
 
-        let packed = sanitise_bytes(packed);
+        Ok(offsets)
+    }
 
-        merkleize(packed)
+    fn num_child_nodes(&self) -> usize {
+        // TODO
+        42
     }
 
     fn num_bytes(&self) -> usize {
         self.iter().fold(0, |acc, item| acc + item.num_bytes())
     }
 
+    fn packed_encoding(&self) -> Vec<u8> {
+        panic!("List should never be packed")
+    }
+
     fn cached_hash_tree_root(
         &self,
         other: &Self::Item,
         cache: &mut TreeHashCache,
         chunk: usize,
-    ) -> Option<usize> {
+    ) -> Result<usize, Error> {
+        /*
         let num_packed_bytes = self.num_bytes();
         let num_leaves = num_sanitized_leaves(num_packed_bytes);
 
@@ -103,6 +146,17 @@ where
         }
 
         Some(chunk + num_nodes)
+        */
+        // TODO
+        Ok(42)
     }
 }
+
+/*
+fn get_packed_leaves<T>(vec: Vec<T>) -> Vec<u8>
+where
+    T: Encodable,
+{
+    //
+}
 */