backend/src/main/java/de/szut/casino/blackjack/BlackJackGameController.java

@@ -57,6 +57,13 @@ public class BlackJackGameController {
         return ResponseEntity.ok(blackJackService.doubleDown(game));
     }
 
+    @PostMapping("/blackjack/{id}/split")
+    public ResponseEntity<Object> split(@PathVariable Long id) {
+        BlackJackGameEntity game = getBlackJackGame(id);
+
+        return ResponseEntity.ok(blackJackService.split(game));
+    }
+
     @PostMapping("/blackjack/start")
     public ResponseEntity<Object> createBlackJackGame(@RequestBody @Valid BetDto betDto) {
         Optional<UserEntity> optionalUser = userService.getCurrentUser();

backend/src/main/java/de/szut/casino/blackjack/BlackJackGameEntity.java

@@ -51,4 +51,15 @@ public class BlackJackGameEntity {
     @JsonManagedReference
     @SQLRestriction("card_type = 'DEALER'")
     private List<CardEntity> dealerCards = new ArrayList<>();
+
+    @OneToMany(mappedBy = "game", cascade = CascadeType.ALL, orphanRemoval = true)
+    @JsonManagedReference
+    @SQLRestriction("card_type = 'PLAYER_SPLIT'")
+    private List<CardEntity> playerSplitCards = new ArrayList<>();
+
+    @Column(name = "split_bet")
+    private BigDecimal splitBet;
+
+    @Column(name = "is_split")
+    private boolean isSplit;
 }

backend/src/main/java/de/szut/casino/blackjack/BlackJackService.java

@@ -2,8 +2,8 @@ package de.szut.casino.blackjack;
 
 import de.szut.casino.user.UserEntity;
 import de.szut.casino.user.UserRepository;
-import jakarta.transaction.Transactional;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
 
 import java.math.BigDecimal;
 import java.util.List;
@@ -85,6 +85,36 @@ public class BlackJackService {
         return game;
     }
 
+    @Transactional
+    public BlackJackGameEntity split(BlackJackGameEntity game) {
+        if (game.getState() != BlackJackState.IN_PROGRESS ||
+                game.getPlayerCards().size() != 2 ||
+                game.isSplit() ||
+                !game.getPlayerCards().get(0).getRank().equals(game.getPlayerCards().get(1).getRank())) {
+            return game;
+        }
+
+        UserEntity user = getUserWithFreshData(game.getUser());
+        BigDecimal splitBet = game.getBet();
+
+        if (user.getBalance().compareTo(splitBet) < 0) {
+            return game;
+        }
+
+        deductBetFromBalance(user, splitBet);
+        game.setSplitBet(splitBet);
+        game.setSplit(true);
+
+        CardEntity card = game.getPlayerCards().remove(1);
+        card.setCardType(CardType.PLAYER_SPLIT);
+        game.getPlayerSplitCards().add(card);
+
+        dealCardToPlayer(game);
+        dealCardToSplitHand(game);
+
+        return processGameBasedOnState(game);
+    }
+
     private BlackJackGameEntity processGameBasedOnState(BlackJackGameEntity game) {
         if (game.getState() != BlackJackState.IN_PROGRESS) {
             this.blackJackGameRepository.delete(game);
@@ -124,13 +154,33 @@ public class BlackJackService {
         }
     }
 
-    private void updateGameStateAndBalance(BlackJackGameEntity game) {
-        game.setState(getState(game));
+    private void dealCardToSplitHand(BlackJackGameEntity game) {
+        CardEntity card = drawCardFromDeck(game);
+        card.setCardType(CardType.PLAYER_SPLIT);
+        game.getPlayerSplitCards().add(card);
+    }
 
-        if (game.getState() == BlackJackState.PLAYER_WON) {
-            updateUserBalance(game, true);
-        } else if (game.getState() == BlackJackState.PLAYER_LOST) {
-            updateUserBalance(game, false);
+    private void updateGameStateAndBalance(BlackJackGameEntity game) {
+        if (game.isSplit()) {
+            int mainHandValue = calculateHandValue(game.getPlayerCards());
+            int splitHandValue = calculateHandValue(game.getPlayerSplitCards());
+
+            if (mainHandValue > 21 && splitHandValue > 21) {
+                game.setState(BlackJackState.PLAYER_LOST);
+                updateUserBalance(game, false);
+            } else if (mainHandValue <= 21 && splitHandValue <= 21) {
+                game.setState(BlackJackState.IN_PROGRESS);
+            } else {
+                game.setState(BlackJackState.IN_PROGRESS);
+            }
+        } else {
+            game.setState(getState(game));
+
+            if (game.getState() == BlackJackState.PLAYER_WON) {
+                updateUserBalance(game, true);
+            } else if (game.getState() == BlackJackState.PLAYER_LOST) {
+                updateUserBalance(game, false);
+            }
         }
     }
 
@@ -155,15 +205,40 @@ public class BlackJackService {
         userRepository.save(user);
     }
 
+    @Transactional
     protected void updateUserBalance(BlackJackGameEntity game, boolean isWin) {
         UserEntity user = getUserWithFreshData(game.getUser());
         BigDecimal totalBet = game.getBet();
         BigDecimal balance = user.getBalance();
 
-        if (isWin) {
-            balance = balance.add(totalBet.multiply(BigDecimal.valueOf(2)));
-        } else if (game.getState() == BlackJackState.DRAW) {
-            balance = balance.add(totalBet);
+        if (game.isSplit()) {
+            totalBet = totalBet.add(game.getSplitBet());
+
+            if (isWin) {
+                int mainHandValue = calculateHandValue(game.getPlayerCards());
+                int splitHandValue = calculateHandValue(game.getPlayerSplitCards());
+                int dealerValue = calculateHandValue(game.getDealerCards());
+
+                if (mainHandValue <= 21 && (dealerValue > 21 || mainHandValue > dealerValue)) {
+                    balance = balance.add(game.getBet().multiply(BigDecimal.valueOf(2)));
+                } else if (mainHandValue == dealerValue) {
+                    balance = balance.add(game.getBet());
+                }
+
+                if (splitHandValue <= 21 && (dealerValue > 21 || splitHandValue > dealerValue)) {
+                    balance = balance.add(game.getSplitBet().multiply(BigDecimal.valueOf(2)));
+                } else if (splitHandValue == dealerValue) {
+                    balance = balance.add(game.getSplitBet());
+                }
+            } else if (game.getState() == BlackJackState.DRAW) {
+                balance = balance.add(totalBet);
+            }
+        } else {
+            if (isWin) {
+                balance = balance.add(totalBet.multiply(BigDecimal.valueOf(2)));
+            } else if (game.getState() == BlackJackState.DRAW) {
+                balance = balance.add(totalBet);
+            }
         }
 
         user.setBalance(balance);

backend/src/main/java/de/szut/casino/blackjack/CardEntity.java

@@ -36,5 +36,5 @@ public class CardEntity {
 }
 
 enum CardType {
-    DECK, PLAYER, DEALER
+    DECK, PLAYER, DEALER, PLAYER_SPLIT
 }