From b344f17b8635b1658a06617f7c4e05e12dbc6d7e Mon Sep 17 00:00:00 2001
From: Jack Robison <jackrobison@lbry.io>
Date: Wed, 14 Jul 2021 12:56:52 -0400
Subject: [PATCH] update RevertableOpStack

---
 lbry/wallet/server/db/revertable.py | 42 +++++++++++++++--------------
 1 file changed, 22 insertions(+), 20 deletions(-)

diff --git a/lbry/wallet/server/db/revertable.py b/lbry/wallet/server/db/revertable.py
index d6e957a7b..604c7c60f 100644
--- a/lbry/wallet/server/db/revertable.py
+++ b/lbry/wallet/server/db/revertable.py
@@ -1,10 +1,10 @@
 import struct
 from string import printable
-from collections import OrderedDict, defaultdict
-from typing import Tuple, List, Iterable, Callable, Optional
+from collections import defaultdict
+from typing import Tuple, Iterable, Callable, Optional
 from lbry.wallet.server.db import DB_PREFIXES
 
-_OP_STRUCT = struct.Struct('>BHH')
+_OP_STRUCT = struct.Struct('>BLL')
 
 
 class RevertableOp:
@@ -30,7 +30,7 @@ class RevertableOp:
         Serialize to bytes
         """
         return struct.pack(
-            f'>BHH{len(self.key)}s{len(self.value)}s', int(self.is_put), len(self.key), len(self.value), self.key,
+            f'>BLL{len(self.key)}s{len(self.value)}s', int(self.is_put), len(self.key), len(self.value), self.key,
             self.value
         )
 
@@ -42,23 +42,12 @@ class RevertableOp:
         :param packed: bytes containing at least one packed revertable op
         :return: tuple of the deserialized op (a put or a delete) and the remaining serialized bytes
         """
-        is_put, key_len, val_len = _OP_STRUCT.unpack(packed[:5])
-        key = packed[5:5 + key_len]
-        value = packed[5 + key_len:5 + key_len + val_len]
+        is_put, key_len, val_len = _OP_STRUCT.unpack(packed[:9])
+        key = packed[9:9 + key_len]
+        value = packed[9 + key_len:9 + key_len + val_len]
         if is_put == 1:
-            return RevertablePut(key, value), packed[5 + key_len + val_len:]
-        return RevertableDelete(key, value), packed[5 + key_len + val_len:]
-
-    @classmethod
-    def unpack_stack(cls, packed: bytes) -> List['RevertableOp']:
-        """
-        Deserialize multiple from bytes
-        """
-        ops = []
-        while packed:
-            op, packed = cls.unpack(packed)
-            ops.append(op)
-        return ops
+            return RevertablePut(key, value), packed[9 + key_len + val_len:]
+        return RevertableDelete(key, value), packed[9 + key_len + val_len:]
 
     def __eq__(self, other: 'RevertableOp') -> bool:
         return (self.is_put, self.key, self.value) == (other.is_put, other.key, other.value)
@@ -134,3 +123,16 @@ class RevertableOpStack:
         for key, ops in self._items.items():
             for op in ops:
                 yield op
+
+    def __reversed__(self):
+        for key, ops in self._items.items():
+            for op in reversed(ops):
+                yield op
+
+    def get_undo_ops(self) -> bytes:
+        return b''.join(op.invert().pack() for op in reversed(self))
+
+    def apply_packed_undo_ops(self, packed: bytes):
+        while packed:
+            op, packed = RevertableOp.unpack(packed)
+            self.append(op)