feat: implement dice game api

backend/src/main/java/de/szut/casino/dice/DiceController.java

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+package de.szut.casino.dice;
+
+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 DiceController {
+    private final UserService userService;
+    private final BalanceService balanceService;
+    private final DiceService diceService;
+
+    public DiceController(UserService userService, BalanceService balanceService, DiceService diceService) {
+        this.userService = userService;
+        this.balanceService = balanceService;
+        this.diceService = diceService;
+    }
+
+    @PostMapping("/dice")
+    public ResponseEntity<Object> rollDice(@RequestBody @Valid DiceDto diceDto) {
+        Optional<UserEntity> optionalUser = userService.getCurrentUser();
+
+        if (optionalUser.isEmpty()) {
+            throw new UserNotFoundException();
+        }
+
+        UserEntity user = optionalUser.get();
+
+        if (!this.balanceService.hasFunds(user, diceDto)) {
+            throw new InsufficientFundsException();
+        }
+
+        return ResponseEntity.ok(diceService.play(user, diceDto));
+    }
+}

backend/src/main/java/de/szut/casino/dice/DiceDto.java

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+package de.szut.casino.dice;
+
+import de.szut.casino.shared.dto.BetDto;
+import jakarta.validation.constraints.DecimalMin;
+import jakarta.validation.constraints.NotNull;
+import lombok.Getter;
+import lombok.Setter;
+
+import java.math.BigDecimal;
+
+@Getter
+@Setter
+public class DiceDto extends BetDto {
+    private boolean rollOver;
+
+    @NotNull
+    @DecimalMin(value = "1.00")
+    private BigDecimal targetValue;
+
+    public DiceDto(BigDecimal betAmount, boolean rollOver, BigDecimal targetValue) {
+        super(betAmount);
+        this.rollOver = rollOver;
+        this.targetValue = targetValue;
+    }
+}

backend/src/main/java/de/szut/casino/dice/DiceResult.java

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+package de.szut.casino.dice;
+
+import java.math.BigDecimal;
+
+public class DiceResult {
+    private boolean win;
+    private BigDecimal payout;
+    private BigDecimal rolledValue;
+
+    public DiceResult(boolean win, BigDecimal payout, BigDecimal rolledValue) {
+        this.win = win;
+        this.payout = payout;
+        this.rolledValue = rolledValue;
+    }
+
+    public boolean isWin() {
+        return win;
+    }
+
+    public void setWin(boolean win) {
+        this.win = win;
+    }
+
+    public BigDecimal getPayout() {
+        return payout;
+    }
+
+    public void setPayout(BigDecimal payout) {
+        this.payout = payout;
+    }
+
+    public BigDecimal getRolledValue() {
+        return rolledValue;
+    }
+
+    public void setRolledValue(BigDecimal rolledValue) {
+        this.rolledValue = rolledValue;
+    }
+}

backend/src/main/java/de/szut/casino/dice/DiceService.java

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+package de.szut.casino.dice;
+
+import de.szut.casino.shared.service.BalanceService;
+import de.szut.casino.user.UserEntity;
+import org.springframework.stereotype.Service;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.util.Random;
+
+@Service
+public class DiceService {
+    private static final int MAX_DICE_VALUE = 100;
+    private final Random random = new Random();
+    private final BalanceService balanceService;
+
+    public DiceService(BalanceService balanceService) {
+        this.balanceService = balanceService;
+    }
+
+    public DiceResult play(UserEntity user, DiceDto diceDto) {
+        balanceService.subtractFunds(user, diceDto.getBetAmount());
+
+        int rolledValue = random.nextInt(MAX_DICE_VALUE) + 1;
+        BigDecimal rolledValueDecimal = BigDecimal.valueOf(rolledValue);
+
+        BigDecimal targetValue = diceDto.getTargetValue();
+        boolean isRollOver = diceDto.isRollOver();
+
+        boolean winConditionMet = isWinConditionMet(rolledValueDecimal, targetValue, isRollOver);
+
+        if (!winConditionMet) {
+            return new DiceResult(false, BigDecimal.ZERO, rolledValueDecimal);
+        }
+
+        BigDecimal winChance = calculateWinChance(targetValue, isRollOver);
+        BigDecimal multiplier = calculateMultiplier(winChance);
+
+        BigDecimal payout = diceDto.getBetAmount().multiply(multiplier);
+        balanceService.addFunds(user, payout);
+
+        return new DiceResult(true, payout, rolledValueDecimal);
+    }
+
+    private boolean isWinConditionMet(BigDecimal rolledValue, BigDecimal targetValue, boolean isRollOver) {
+        if (isRollOver) {
+            return rolledValue.compareTo(targetValue) > 0;
+        }
+
+        return rolledValue.compareTo(targetValue) < 0;
+    }
+
+    private BigDecimal calculateWinChance(BigDecimal targetValue, boolean isRollOver) {
+        if (isRollOver) {
+            return BigDecimal.valueOf(MAX_DICE_VALUE).subtract(targetValue);
+        }
+
+        return targetValue.subtract(BigDecimal.ONE);
+    }
+
+    private BigDecimal calculateMultiplier(BigDecimal winChance) {
+        if (winChance.compareTo(BigDecimal.ZERO) > 0) {
+            return BigDecimal.valueOf(MAX_DICE_VALUE - 1).divide(winChance, 4, RoundingMode.HALF_UP);
+        }
+
+        return BigDecimal.ZERO;
+    }
+}