[#6] feat: Create GameService

1. 야구 게임방의 서비스 레이어입니다.
2. 게임 만들기, 게임 참가하기, 게임진행하기, 게임결과받기 의 기본기능이 있습니다.

BE/baseball/src/main/java/team9/baseball/service/GameService.java

@@ -0,0 +1,104 @@
+package team9.baseball.service;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+import team9.baseball.DTO.response.GameStatusDTO;
+import team9.baseball.domain.aggregate.game.Game;
+import team9.baseball.domain.aggregate.team.Team;
+import team9.baseball.domain.aggregate.user.User;
+import team9.baseball.domain.enums.PitchResult;
+import team9.baseball.domain.enums.Venue;
+import team9.baseball.exception.NotFoundException;
+import team9.baseball.repository.GameRepository;
+import team9.baseball.repository.TeamRepository;
+import team9.baseball.repository.UserRepository;
+
+@Service
+public class GameService {
+    private final GameRepository gameRepository;
+    private final TeamRepository teamRepository;
+    private final UserRepository userRepository;
+
+    @Autowired
+    public GameService(GameRepository gameRepository, TeamRepository teamRepository, UserRepository userRepository) {
+        this.gameRepository = gameRepository;
+        this.teamRepository = teamRepository;
+        this.userRepository = userRepository;
+    }
+
+    public void applyPitchResult(long userId, PitchResult pitchResult) {
+        User user = getUser(userId);
+        if (user.getCurrentGameId() == null) {
+            throw new RuntimeException(userId + "사용자는 게임중이 아닙니다.");
+        }
+        Game game = getGame(user.getCurrentGameId());
+        Team awayTeam = getTeam(game.getAwayTeamId());
+        Team homeTeam = getTeam(game.getHomeTeamId());
+
+        //현재 내가 공격팀이면 공을 던질 수 없다.
+        if (game.getCurrentHalves() == user.getCurrentGameVenue().getHalves()) {
+            throw new RuntimeException(userId + "번 사용자는 현재 공격팀입니다.");
+        }
+
+        switch (pitchResult) {
+            case HIT:
+                game.proceedHit(awayTeam, homeTeam);
+                break;
+            case STRIKE:
+                game.proceedStrike(awayTeam, homeTeam);
+                break;
+            case BALL:
+                game.proceedBall(awayTeam, homeTeam);
+                break;
+        }
+        gameRepository.save(game);
+    }
+
+    public GameStatusDTO getCurrentGameStatus(long userId) {
+        User user = getUser(userId);
+        if (user.getCurrentGameId() == null) {
+            throw new RuntimeException(userId + "사용자는 게임중이 아닙니다.");
+        }
+        Game game = getGame(user.getCurrentGameId());
+        Team awayTeam = getTeam(game.getAwayTeamId());
+        Team homeTeam = getTeam(game.getHomeTeamId());
+
+        return GameStatusDTO.of(game, awayTeam, homeTeam, user.getCurrentGameVenue());
+    }
+
+    public void createNewGame(long userId, int awayTeamId, int homeTeamId) {
+        User user = getUser(userId);
+        Team awayTeam = getTeam(awayTeamId);
+        Team homeTeam = getTeam(homeTeamId);
+
+        Game game = new Game(awayTeam, homeTeam);
+        game = gameRepository.save(game);
+    }
+
+    public void joinGame(long userId, long gameId, Venue venue) {
+        User user = getUser(userId);
+        if (user.getCurrentGameId() != null) {
+            throw new RuntimeException(userId + "사용자는 이미 게임중입니다.");
+        }
+        Game game = getGame(gameId);
+        if (userRepository.existsByCurrentGameIdAndCurrentGameVenue(gameId, venue)) {
+            throw new RuntimeException(gameId + "번 게임의 " + venue + "팀은 다른 사용자가 참가했습니다.");
+        }
+
+        user.setCurrentGameId(gameId);
+        user.setCurrentGameVenue(venue);
+        userRepository.save(user);
+    }
+
+    private User getUser(long userId) {
+        return userRepository.findById(userId).orElseThrow(() -> new NotFoundException(userId + " 사용자는 존재하지 않습니다."));
+    }
+
+    private Game getGame(long gameId) {
+        return gameRepository.findById(gameId).orElseThrow(() -> new NotFoundException(gameId + "번 게임은 존재하지 않습니다."));
+    }
+
+    private Team getTeam(int teamId) {
+        return teamRepository.findById(teamId).orElseThrow(() -> new NotFoundException(teamId + "번 팀은 존재하지 않습니다."));
+    }
+}