diff --git a/src/lib/chess/utils.ts b/src/lib/chess/game.ts
similarity index 100%
rename from src/lib/chess/utils.ts
rename to src/lib/chess/game.ts
diff --git a/src/lib/chess/types.ts b/src/lib/chess/types.ts
index dde6bce..4db0114 100644
--- a/src/lib/chess/types.ts
+++ b/src/lib/chess/types.ts
@@ -1,17 +1,46 @@
-import { Game } from "./utils";
+import { Game } from "./game";
 export type GameListener = (board: Game) => void;
 
-export enum Piece {
-  EMPTY = 0,
-  KING = 1,
-  QUEEN = 2,
-  ROOK = 3,
-  BISHOP = 4,
-  KNIGHT = 5,
-  PAWN = 6,
+export enum MoveFlag {
+  NORMAL = 0,
+  PAWN_DOUBLE = 1,
+  EN_PASSANT = 2,
+  CASTLE_KING = 3,
+  CASTLE_QUEEN = 4,
+  PROMOTION = 5,
+  CAPTURE = 6,
+  CAPTURE_PROMOTE = 7,
+}
 
-  WHITE = 8,
-  BLACK = 16,
+export enum Promotion {
+  QUEEN = 0,
+  ROOK = 1,
+  BISHOP = 2,
+  KNIGHT = 3,
+}
+
+export enum Capture {
+  NONE = 0,
+  PAWN = 1,
+  KNIGHT = 2,
+  BISHOP = 3,
+  ROOK = 4,
+  QUEEN = 5,
+}
+
+export enum Piece {
+  // bit 0-2: piece type (0-6)
+  EMPTY = 0,
+  QUEEN = 1,
+  ROOK = 2,
+  BISHOP = 3,
+  KNIGHT = 4,
+  PAWN = 5,
+  KING = 6,
+
+  // bit 3: color (0-1)
+  WHITE = 0<<3,
+  BLACK = 1<<3,
 }
 
 export const CHAR_TO_PIECE: Record<string, number> = {
diff --git a/src/routes/+page.svelte b/src/routes/+page.svelte
index ea6797a..51577d3 100644
--- a/src/routes/+page.svelte
+++ b/src/routes/+page.svelte
@@ -1,6 +1,6 @@
 <script lang="ts">
   import { PIECE_TO_CHAR } from "$lib/chess/types";
-  import { boardToAscii, Game, startFEN } from "$lib/chess/utils";
+  import { boardToAscii, Game, startFEN } from "$lib/chess/game";
 
   let showIndex = $state(false);
   let fen = $state(startFEN);