JSON models and handling errors

{
  "order_id": 9081,
  "status": "SHIPPED",
  "items": [ { "name": "Kurta", "qty": 1 } ],
  "coupon": null,
  "eta_days": 3
}

@Serializable
data class OrderDto(
    @SerialName("order_id") val orderId: Int,
    val status: String,
    val items: List<ItemDto>,
    val coupon: String? = null,            // may be null or missing
    @SerialName("eta_days") val etaDays: Int = 0,
)

@Serializable
data class ItemDto(val name: String, val qty: Int)

val json = Json { ignoreUnknownKeys = true }
val order = json.decodeFromString<OrderDto>(responseText)

sealed interface ProductsUiState {
    data object Loading : ProductsUiState
    data class Success(val products: List<Product>) : ProductsUiState
    data class Error(val message: String) : ProductsUiState
}

class ProductsViewModel(private val repo: ProductRepository) : ViewModel() {
    private val _state = MutableStateFlow<ProductsUiState>(ProductsUiState.Loading)
    val state: StateFlow<ProductsUiState> = _state.asStateFlow()

    init { load() }

    fun load() {
        viewModelScope.launch {
            _state.value = ProductsUiState.Loading
            _state.value = try {
                ProductsUiState.Success(repo.productsIn("sarees"))
            } catch (e: IOException) {
                ProductsUiState.Error("No internet connection")
            } catch (e: HttpException) {
                ProductsUiState.Error("Server error (${e.code()})")
            }
        }
    }
}

@Composable
fun ProductsScreen(state: ProductsUiState, onRetry: () -> Unit) {
    when (state) {
        ProductsUiState.Loading -> CircularProgressIndicator()
        is ProductsUiState.Success -> LazyColumn { items(state.products, key = { it.id }) { Text(it.name) } }
        is ProductsUiState.Error -> Column {
            Text(state.message)
            Button(onClick = onRetry) { Text("Retry") }
        }
    }
}