feat: implement coinflip api

backend/src/main/java/de/szut/casino/coinflip/CoinSide.java

@@ -0,0 +1,6 @@
+package de.szut.casino.coinflip;
+
+public enum CoinSide {
+    HEAD,
+    TAILS;
+}

backend/src/main/java/de/szut/casino/coinflip/CoinflipController.java

@@ -0,0 +1,45 @@
+package de.szut.casino.coinflip;
+
+import de.szut.casino.exceptionHandling.exceptions.InsufficientFundsException;
+import de.szut.casino.exceptionHandling.exceptions.UserNotFoundException;
+import de.szut.casino.shared.service.BalanceService;
+import de.szut.casino.user.UserEntity;
+import de.szut.casino.user.UserService;
+import jakarta.validation.Valid;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.Optional;
+
+@RestController
+public class CoinflipController {
+    private final UserService userService;
+    private final BalanceService balanceService;
+    private final CoinflipService coinflipService;
+
+    public CoinflipController(UserService userService, BalanceService balanceService, CoinflipService coinflipService) {
+        this.userService = userService;
+        this.balanceService = balanceService;
+        this.coinflipService = coinflipService;
+    }
+
+
+    @PostMapping("/coinflip")
+    public ResponseEntity<Object> coinFlip(@RequestBody @Valid CoinflipDto coinflipDto) {
+        Optional<UserEntity> optionalUser = userService.getCurrentUser();
+
+        if (optionalUser.isEmpty()) {
+            throw new UserNotFoundException();
+        }
+
+        UserEntity user = optionalUser.get();
+
+        if (!this.balanceService.hasFunds(user, coinflipDto)) {
+            throw new InsufficientFundsException();
+        }
+
+        return ResponseEntity.ok(coinflipService.play(user, coinflipDto));
+    }
+}

backend/src/main/java/de/szut/casino/coinflip/CoinflipDto.java

@@ -0,0 +1,20 @@
+package de.szut.casino.coinflip;
+
+import de.szut.casino.shared.dto.BetDto;
+import jakarta.validation.constraints.NotNull;
+import lombok.Getter;
+import lombok.Setter;
+
+import java.math.BigDecimal;
+
+@Getter
+@Setter
+public class CoinflipDto extends BetDto {
+    @NotNull(message = "chosen side cannot be null")
+    private CoinSide coinSide;
+
+    public CoinflipDto(BigDecimal betAmount, CoinSide coinSide) {
+        super(betAmount);
+        this.coinSide = coinSide;
+    }
+}

backend/src/main/java/de/szut/casino/coinflip/CoinflipResult.java

@@ -0,0 +1,15 @@
+package de.szut.casino.coinflip;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.Setter;
+
+import java.math.BigDecimal;
+
+@AllArgsConstructor
+@Setter
+@Getter
+public class CoinflipResult {
+    private boolean isWin;
+    private BigDecimal payout;
+}

backend/src/main/java/de/szut/casino/coinflip/CoinflipService.java

@@ -0,0 +1,34 @@
+package de.szut.casino.coinflip;
+
+import de.szut.casino.shared.service.BalanceService;
+import de.szut.casino.user.UserEntity;
+import org.springframework.stereotype.Service;
+
+import java.math.BigDecimal;
+import java.util.Random;
+
+@Service
+public class CoinflipService {
+    private final Random random = new Random();
+    private final BalanceService balanceService;
+
+    public CoinflipService(BalanceService balanceService) {
+        this.balanceService = balanceService;
+    }
+
+    public CoinflipResult play(UserEntity user, CoinflipDto coinflipDto) {
+        this.balanceService.subtractFunds(user, coinflipDto.getBetAmount());
+
+        CoinflipResult coinflipResult = new CoinflipResult(false, BigDecimal.ZERO);
+        CoinSide coinSide = this.random.nextBoolean() ? CoinSide.HEAD : CoinSide.TAILS;
+        if (coinSide == coinflipDto.getCoinSide()) {
+            coinflipResult.setWin(true);
+
+            BigDecimal payout = coinflipDto.getBetAmount().multiply(BigDecimal.TWO);
+            this.balanceService.addFunds(user, payout);
+            coinflipResult.setPayout(payout);
+        }
+
+        return coinflipResult;
+    }
+}

backend/src/main/java/de/szut/casino/shared/service/BalanceService.java

@@ -9,7 +9,7 @@ import java.math.BigDecimal;
 
 @Service
 public class BalanceService {
-    private UserRepository userRepository;
+    private final UserRepository userRepository;
 
     public BalanceService(UserRepository userRepository) {
         this.userRepository = userRepository;