data class UserDto(
    val id: String,
    val first_name: String,
    val last_name: String,
    val profile_url: String?
) {
    fun toDomainModel(): User = User(
        id = id,
        fullName = "$first_name $last_name",
        imageUrl = profile_url ?: "default_url"
    )
}

interface UserApi {
    @GET("/users/{userId}")
    suspend fun getUserProfile(@Path("userId") userId: String): UserDto
}

// 순수 비즈니스 Domain Model
data class User(val id: String, val fullName: String, val imageUrl: String)

// 계약서 (Interface) — 구현체 없음
interface UserRepository {
    suspend fun getUserProfile(userId: String): Result<User>
}

// 단일 책임 UseCase
class GetUserProfileUseCase(
    private val userRepository: UserRepository // 인터페이스에만 의존
) {
    suspend operator fun invoke(userId: String): Result<User> {
        if (userId.isBlank())
            return Result.failure(IllegalArgumentException("유효하지 않은 유저 ID"))
        return userRepository.getUserProfile(userId)
    }
}

class UserRepositoryImpl(
    private val userApi: UserApi
) : UserRepository {
    override suspend fun getUserProfile(userId: String): Result<User> {
        return try {
            val dto = userApi.getUserProfile(userId)
            Result.success(dto.toDomainModel()) // DTO → Domain Model 매핑
        } catch (e: Exception) {
            Result.failure(e)
        }
    }
}

sealed class UserUiState {
    object Loading : UserUiState()
    data class Success(val user: User) : UserUiState()
    data class Error(val message: String) : UserUiState()
}

@HiltViewModel
class UserViewModel @Inject constructor(
    private val getUserProfileUseCase: GetUserProfileUseCase
) : ViewModel() {

    private val _uiState = MutableStateFlow<UserUiState>(UserUiState.Loading)
    val uiState: StateFlow<UserUiState> = _uiState.asStateFlow()

    fun fetchUser(userId: String) {
        viewModelScope.launch {
            _uiState.value = UserUiState.Loading
            getUserProfileUseCase(userId)
                .onSuccess { _uiState.value = UserUiState.Success(it) }
                .onFailure { _uiState.value = UserUiState.Error(it.message ?: "에러") }
        }
    }
}

@Composable
fun UserProfileScreen(viewModel: UserViewModel = hiltViewModel()) {
    val uiState by viewModel.uiState.collectAsState()
    when (uiState) {
        is UserUiState.Loading -> CircularProgressIndicator()
        is UserUiState.Success -> Text("안녕하세요, ${(uiState as UserUiState.Success).user.fullName}님!")
        is UserUiState.Error  -> Text("에러: ${(uiState as UserUiState.Error).message}")
    }
}