Game.returnToMove(x) where x >= 0 returns game state at move x

packages/server/services/Game.v2.js

@@ -238,14 +238,20 @@ const Game = ({gameData = {}, gameRecord = []} = {}) => {
       return { game: this, group };
     },
 
-    returnToMove: function(idx) {
+    returnToMove: function(lastMove) {
-      if (idx < 0) {
       const { komi, handicap, boardSize } = this;
+      if (lastMove === 0) {
+        return Game({
+          gameData: { komi, handicap, boardSize }
+        }).initGame();
+      }
+      const length = this.gameRecord.length;
+      const index = lastMove < 0 ? length + lastMove : lastMove;
+      if (lastMove >= length && lastMove > 0) return this;
       return Game({ 
         gameData: { komi, handicap, boardSize }, 
-          gameRecord: [...this.gameRecord.slice(0, this.gameRecord.length + idx)]
+        gameRecord: [...this.gameRecord.slice(0, index)]
-        })
+      });
-      }
     }
   }
 };

packages/server/test/Game.v2.spec.js

@@ -407,6 +407,12 @@ describe('capture logic: snapback, ko and playing in eyes', () => {
 describe('Game history functionality', () => {
   const firstMove =   { player: 'black', pos: { x: 4, y: 4 }};
   const secondMove =  { player: 'white', pos: { x: 16, y: 16 }};
+  const thirdMove =   { player: 'black', pos: { x: 16, y: 4 } };
+  const fourthMove =  { player: 'white', pos: { x: 4, y: 16 }};
+  const fifthMove =   { player: 'black', pos: { x: 10, y: 4 } };
+  const sixthMove =   { player: 'white', pos: { x: 4, y: 10 }};
+  const seventhMove = { player: 'black', pos: { x: 10, y: 16 } };
+  const eighthMove =  { player: 'white', pos: { x: 16, y: 10 }};
 
   it('makeMove creates gameRecord item', done => {
     Game().initGame()
@@ -425,14 +431,14 @@ describe('Game history functionality', () => {
   const rewoundGame = () => Game().initGame()
     .makeMove(firstMove)
     .makeMove(secondMove)
-  .makeMove({ player: 'black', pos: { x: 16, y: 4 } })
+    .makeMove(thirdMove)
     .returnToMove(-1);
 
   it('Game.returnToMove returns new Game with gameRecord', done => {
     rewoundGame()
       .gameRecord.should.eql([ firstMove, secondMove ])
     done();
-  })
+  });
   
   it('Game.returnToMove returns new Game with new board state', done => {
     rewoundGame()
@@ -442,6 +448,27 @@ describe('Game history functionality', () => {
     rewoundGame()
       .boardState['16-16'].stone.should.eql(-1);
     done();
+  });
+
+  const resetGame = () => [
+    firstMove, secondMove, thirdMove, fourthMove, fifthMove, sixthMove, seventhMove, eighthMove
+  ].reduce((game, move) => game.makeMove(move), Game().initGame());
+
+  it('Game.returnToMove(0) returns to init board state', done => {
+    const erasedGame = resetGame()
+      .returnToMove(0)
+    erasedGame.gameRecord.should.eql([])
+    erasedGame.boardState['4-4'].stone.should.eql(0)
+    done();
+  });
+
+  it('Game.returnToMove(5) returns to state after 5th move', done => {
+    const fifthMoveGame = resetGame()
+      .returnToMove(5);
+    fifthMoveGame.gameRecord.should.eql([firstMove, secondMove, thirdMove, fourthMove, fifthMove]);
+    fifthMoveGame.boardState['10-4'].stone.should.eql(1)
+    fifthMoveGame.boardState['4-10'].stone.should.eql(0)
+    done();
   })
 })