feat: UserSignUpPolicy Domain Service 구현 및 SignUp 로직에 반영

src/main/java/com/gloddy/server/auth/domain/service/UserFactory.java

@@ -3,14 +3,20 @@
 import com.gloddy.server.auth.domain.User;
 import com.gloddy.server.auth.domain.vo.Phone;
 import com.gloddy.server.auth.domain.vo.School;
+import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Component;
 
 import static com.gloddy.server.auth.domain.dto.AuthRequest.*;
 
 @Component
+@RequiredArgsConstructor
 public class UserFactory {
 
+    private final UserSignUpPolicy userSignUpPolicy;
+
     public User getUser(SignUp request) {
+        userSignUpPolicy.validate(request.getPhoneNumber());
+
         Phone phone = getPhone(request.getPhoneNumber());
         School school = getSchool(request.getSchoolInfo());
         return User.builder()

src/main/java/com/gloddy/server/auth/domain/service/UserSignUpPolicy.java

@@ -0,0 +1,27 @@
+package com.gloddy.server.auth.domain.service;
+
+import com.gloddy.server.auth.domain.User;
+import com.gloddy.server.auth.domain.vo.Phone;
+import com.gloddy.server.auth.exception.AlreadyUserSignUpException;
+import com.gloddy.server.user.infra.repository.UserJpaRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+
+import java.util.Optional;
+
+@Component
+@RequiredArgsConstructor
+public class UserSignUpPolicy {
+
+    private final UserJpaRepository userJpaRepository;
+
+    public void validate(String phoneNumber) {
+        Phone phone = new Phone(phoneNumber);
+
+        Optional<User> user = userJpaRepository.findByPhone(phone);
+
+        if (user.isPresent()) {
+            throw new AlreadyUserSignUpException();
+        }
+    }
+}