refactor: balance game type을 enum으로 변경한다

src/main/java/net/teumteum/user/domain/BalanceGameType.java

@@ -0,0 +1,34 @@
+package net.teumteum.user.domain;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.BiFunction;
+import net.teumteum.user.domain.response.InterestQuestionResponse;
+
+public enum BalanceGameType {
+
+    BALANCE("balance", (users, interestQuestion) -> interestQuestion.getBalanceGame(users)),
+    STORY("story", (users, interestQuestion) -> interestQuestion.getStoryGame(users)),
+    ;
+
+    private final String value;
+    private final BiFunction<List<User>, InterestQuestion, InterestQuestionResponse> behavior;
+
+    BalanceGameType(String value, BiFunction<List<User>, InterestQuestion, InterestQuestionResponse> behavior) {
+        this.value = value;
+        this.behavior = behavior;
+    }
+
+    public static BalanceGameType of(String value) {
+        return Arrays.stream(BalanceGameType.values())
+            .filter(type -> type.value.equals(value))
+            .findAny()
+            .orElseThrow(
+                () -> new IllegalArgumentException("\"" + value + "\" 에 해당하는 enum값을 찾을 수 없습니다.")
+            );
+    }
+
+    public InterestQuestionResponse getInterestQuestionResponse(List<User> users, InterestQuestion interestQuestion) {
+        return behavior.apply(users, interestQuestion);
+    }
+}

src/main/java/net/teumteum/user/service/UserService.java

@@ -2,6 +2,7 @@
 
 import java.util.List;
 import lombok.RequiredArgsConstructor;
+import net.teumteum.user.domain.BalanceGameType;
 import net.teumteum.user.domain.InterestQuestion;
 import net.teumteum.user.domain.User;
 import net.teumteum.user.domain.UserRepository;
@@ -76,9 +77,6 @@ public InterestQuestionResponse getInterestQuestionByUserIds(List<Long> userIds,
             }
         );
 
-        if (type.equals("balance")) {
-            return interestQuestion.getBalanceGame(users);
-        }
-        return interestQuestion.getStoryGame(users);
+        return BalanceGameType.of(type).getInterestQuestionResponse(users, interestQuestion);
     }
 }