diff --git a/Cargo.lock b/Cargo.lock
index 08cb49a8..469b3895 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -147,6 +147,15 @@ version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
+[[package]]
+name = "bitmaps"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "031043d04099746d8db04daf1fa424b2bc8bd69d92b25962dcde24da39ab64a2"
+dependencies = [
+ "typenum",
+]
+
 [[package]]
 name = "block-buffer"
 version = "0.10.3"
@@ -666,6 +675,20 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b9e0384b61958566e926dc50660321d12159025e767c18e043daf26b70104c39"
 
+[[package]]
+name = "im"
+version = "15.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0acd33ff0285af998aaf9b57342af478078f53492322fafc47450e09397e0e9"
+dependencies = [
+ "bitmaps",
+ "rand_core",
+ "rand_xoshiro",
+ "sized-chunks",
+ "typenum",
+ "version_check",
+]
+
 [[package]]
 name = "indexmap"
 version = "1.9.2"
@@ -801,6 +824,7 @@ dependencies = [
  "enum_dispatch",
  "flate2",
  "fxhash",
+ "im",
  "itertools",
  "js-sys",
  "num",
@@ -1395,6 +1419,15 @@ dependencies = [
  "rand_core",
 ]
 
+[[package]]
+name = "rand_xoshiro"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6f97cdb2a36ed4183de61b2f824cc45c9f1037f28afe0a322e9fff4c108b5aaa"
+dependencies = [
+ "rand_core",
+]
+
 [[package]]
 name = "rayon"
 version = "1.6.1"
@@ -1635,6 +1668,16 @@ version = "0.3.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7bd3e3206899af3f8b12af284fafc038cc1dc2b41d1b89dd17297221c5d225de"
 
+[[package]]
+name = "sized-chunks"
+version = "0.6.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "16d69225bde7a69b235da73377861095455d298f2b970996eec25ddbb42b3d1e"
+dependencies = [
+ "bitmaps",
+ "typenum",
+]
+
 [[package]]
 name = "smallvec"
 version = "1.10.0"
diff --git a/crates/loro-internal/Cargo.toml b/crates/loro-internal/Cargo.toml
index 9f766ec3..ae0069c9 100644
--- a/crates/loro-internal/Cargo.toml
+++ b/crates/loro-internal/Cargo.toml
@@ -32,6 +32,7 @@ tracing = { version = "0.1.37" }
 append-only-bytes = { version = "0.1.4", features = ["u32_range"] }
 itertools = "0.10.5"
 enum_dispatch = "0.3.11"
+im = "15.1.0"
 
 [dev-dependencies]
 serde_json = "1.0.87"
diff --git a/crates/loro-internal/src/refactor/arena.rs b/crates/loro-internal/src/refactor/arena.rs
new file mode 100644
index 00000000..8470a880
--- /dev/null
+++ b/crates/loro-internal/src/refactor/arena.rs
@@ -0,0 +1,13 @@
+use im::Vector;
+
+use crate::container::{ContainerID, ContainerIdx};
+
+/// This is shared between [OpLog] and [AppState].
+/// It uses a immutable data structure inside so that we have O(1) clone time.
+/// It can make sharing data between threads easier.
+///
+#[derive(Clone)]
+pub(super) struct SharedArena {
+    containers: Vector<ContainerID>,
+    id_to_idx: im::HashMap<ContainerID, ContainerIdx>,
+}
diff --git a/crates/loro-internal/src/refactor/diff_calc.rs b/crates/loro-internal/src/refactor/diff_calc.rs
new file mode 100644
index 00000000..7afc84fb
--- /dev/null
+++ b/crates/loro-internal/src/refactor/diff_calc.rs
@@ -0,0 +1,19 @@
+use fxhash::FxHashMap;
+
+use crate::container::ContainerIdx;
+
+/// Calculate the diff between two versions. given [OpLog][super::oplog::OpLog]
+/// and [AppState][super::state::AppState].
+pub(super) struct DiffCalculator {
+    calc: FxHashMap<ContainerIdx, ContainerDiffCalculator>,
+}
+
+enum ContainerDiffCalculator {
+    Text(TextDiffCalculator),
+    Map(MapDiffCalculator),
+    List(MapDiffCalculator),
+}
+
+struct TextDiffCalculator {}
+struct MapDiffCalculator {}
+struct ListDiffCalculator {}
diff --git a/crates/loro-internal/src/refactor/mod.rs b/crates/loro-internal/src/refactor/mod.rs
index 3b6df870..2d7b2f7d 100644
--- a/crates/loro-internal/src/refactor/mod.rs
+++ b/crates/loro-internal/src/refactor/mod.rs
@@ -1,3 +1,5 @@
+pub(super) mod arena;
 mod container;
+pub(super) mod diff_calc;
 pub mod oplog;
 mod state;
diff --git a/crates/loro-internal/src/refactor/state.rs b/crates/loro-internal/src/refactor/state.rs
index 288c3628..4461793e 100644
--- a/crates/loro-internal/src/refactor/state.rs
+++ b/crates/loro-internal/src/refactor/state.rs
@@ -1,7 +1,14 @@
 use enum_dispatch::enum_dispatch;
 use fxhash::FxHashMap;
 
-use crate::{container::ContainerID, InternalString, VersionVector};
+use crate::{
+    container::{ContainerID, ContainerIdx},
+    event::Diff,
+    version::Frontiers,
+    InternalString, VersionVector,
+};
+
+use super::arena::SharedArena;
 
 mod list;
 mod map;
@@ -9,12 +16,15 @@ mod text;
 
 #[enum_dispatch]
 pub trait ContainerState: Clone {
-    fn apply_diff(&mut self);
+    fn apply_diff(&mut self, diff: Diff);
 }
 
+#[derive(Clone)]
 pub struct AppState {
     vv: VersionVector,
-    state: FxHashMap<ContainerID, State>,
+    frontiers: Frontiers,
+    state: FxHashMap<ContainerIdx, State>,
+    arena: SharedArena,
 }
 
 #[enum_dispatch(ContainerState)]
@@ -28,8 +38,29 @@ pub enum State {
 #[derive(Clone)]
 pub struct ListState {}
 
+impl ContainerState for ListState {
+    fn apply_diff(&mut self, diff: Diff) {}
+}
+
 #[derive(Clone)]
 pub struct MapState {}
+impl ContainerState for MapState {
+    fn apply_diff(&mut self, diff: Diff) {}
+}
 
 #[derive(Clone)]
 pub struct TextState {}
+impl ContainerState for TextState {
+    fn apply_diff(&mut self, diff: Diff) {}
+}
+
+pub struct AppStateDiff {
+    from: VersionVector,
+    to: VersionVector,
+    changes: Vec<ContainerStateDiff>,
+}
+
+pub struct ContainerStateDiff {
+    id: ContainerIdx,
+    diff: Diff,
+}