refactor: use reverse walker (#938)

Co-authored-by: lambdaclass-user <github@lambdaclass.com>

crates/storage/db/src/abstraction/cursor.rs

@@ -34,6 +34,16 @@ pub trait DbCursorRO<'tx, T: Table> {
     ) -> Result<Walker<'cursor, 'tx, T, Self>, Error>
     where
         Self: Sized;
+
+    /// Returns an iterator that walks backwards through the table. If `start_key`
+    /// is None, starts from the last entry of the table. If it not, starts at a key
+    /// greater or equal than the key value wrapped inside Some().
+    fn walk_back<'cursor>(
+        &'cursor mut self,
+        start_key: Option<T::Key>,
+    ) -> Result<ReverseWalker<'cursor, 'tx, T, Self>, Error>
+    where
+        Self: Sized;
 }
 
 /// Read only cursor over DupSort table.

crates/storage/db/src/abstraction/mock.rs

@@ -3,7 +3,9 @@ use std::collections::BTreeMap;
 
 use crate::{
     common::{PairResult, ValueOnlyResult},
-    cursor::{DbCursorRO, DbCursorRW, DbDupCursorRO, DbDupCursorRW, DupWalker, Walker},
+    cursor::{
+        DbCursorRO, DbCursorRW, DbDupCursorRO, DbDupCursorRW, DupWalker, ReverseWalker, Walker,
+    },
     database::{Database, DatabaseGAT},
     table::{DupSort, Table},
     transaction::{DbTx, DbTxGAT, DbTxMut, DbTxMutGAT},
@@ -132,6 +134,16 @@ impl<'tx, T: Table> DbCursorRO<'tx, T> for CursorMock {
     {
         todo!()
     }
+
+    fn walk_back<'cursor>(
+        &'cursor mut self,
+        _start_key: Option<T::Key>,
+    ) -> Result<ReverseWalker<'cursor, 'tx, T, Self>, Error>
+    where
+        Self: Sized,
+    {
+        todo!()
+    }
 }
 
 impl<'tx, T: DupSort> DbDupCursorRO<'tx, T> for CursorMock {

crates/storage/db/src/abstraction/table.rs

@@ -37,9 +37,9 @@ pub trait Decode: Send + Sync + Sized + Debug {
 }
 
 /// Generic trait that enforces the database key to implement [`Encode`] and [`Decode`].
-pub trait Key: Encode + Decode + Ord {}
+pub trait Key: Encode + Decode + Ord + Clone {}
 
-impl<T> Key for T where T: Encode + Decode + Ord {}
+impl<T> Key for T where T: Encode + Decode + Ord + Clone {}
 
 /// Generic trait that enforces the database value to implement [`Compress`] and [`Decompress`].
 pub trait Value: Compress + Decompress + Serialize {}

crates/storage/db/src/implementation/mdbx/cursor.rs

@@ -3,7 +3,9 @@
 use std::{borrow::Cow, marker::PhantomData};
 
 use crate::{
-    cursor::{DbCursorRO, DbCursorRW, DbDupCursorRO, DbDupCursorRW, DupWalker, Walker},
+    cursor::{
+        DbCursorRO, DbCursorRW, DbDupCursorRO, DbDupCursorRW, DupWalker, ReverseWalker, Walker,
+    },
     table::{Compress, DupSort, Encode, Table},
     tables::utils::*,
     Error,
@@ -81,6 +83,27 @@ impl<'tx, K: TransactionKind, T: Table> DbCursorRO<'tx, T> for Cursor<'tx, K, T>
 
         Ok(Walker::new(self, start))
     }
+
+    fn walk_back<'cursor>(
+        &'cursor mut self,
+        start_key: Option<T::Key>,
+    ) -> Result<ReverseWalker<'cursor, 'tx, T, Self>, Error>
+    where
+        Self: Sized,
+    {
+        if let Some(start_key) = start_key {
+            let start = self
+                .inner
+                .set_range(start_key.encode().as_ref())
+                .map_err(|e| Error::Read(e.into()))?
+                .map(decoder::<T>);
+
+            return Ok(ReverseWalker::new(self, start))
+        }
+
+        let start = self.last().transpose();
+        Ok(ReverseWalker::new(self, start))
+    }
 }
 
 impl<'tx, K: TransactionKind, T: DupSort> DbDupCursorRO<'tx, T> for Cursor<'tx, K, T> {