[FEATURE] #15 : 사용자 회원가입 유스케이스 구현

core/domain/src/main/java/com/wap/wapp/core/domain/usecase/auth/SignInUseCase.kt

@@ -0,0 +1,33 @@
+package com.wap.wapp.core.domain.usecase.auth
+
+import com.wap.wapp.core.data.repository.auth.AuthRepository
+import com.wap.wapp.core.data.repository.user.UserRepository
+import com.wap.wapp.core.domain.model.AuthState
+import com.wap.wapp.core.domain.model.AuthState.SIGN_IN
+import com.wap.wapp.core.domain.model.AuthState.SIGN_UP
+import dagger.hilt.android.scopes.ActivityScoped
+import javax.inject.Inject
+
+@ActivityScoped
+class SignInUseCase @Inject constructor(
+    private val authRepository: AuthRepository,
+    private val userRepository: UserRepository,
+) {
+    suspend operator fun invoke(email: String): Result<AuthState> {
+        return runCatching {
+            val userId = authRepository.signIn(email)
+                .getOrThrow()
+
+            userRepository.getUserProfile(userId)
+                .onFailure { exception ->
+                    // 만약 사용자를 찾을 수 없는 경우, 회원가입
+                    val userNotFoundException = IllegalStateException()
+                    if (exception == userNotFoundException) {
+                        return Result.success(SIGN_UP)
+                    }
+                }
+            // 사용자를 찾은 경우, 로그인
+            SIGN_IN
+        }
+    }
+}