MakePaymentViewModel.kt

/* Copyright 2022 Google LLC.	
   SPDX-License-Identifier: Apache-2.0 */

data class MakePaymentUiState(
    val paymentInformation: PaymentModel,
    val isLoading: Boolean = false,
    // PaymentResult models the application state of this particular payment attempt,
    // `null` represents the payment hasn't been made yet.
    val paymentResult: PaymentResult? = null
)

class MakePaymentViewModel(...) : ViewModel() {

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

    // Protecting makePayment from concurrent callers
    // If a payment is in progress, don't trigger it again
    private var makePaymentJob: Job? = null

    fun makePayment() {
        if (makePaymentJob != null) return

        makePaymentJob = viewModelScope.launch {
            try {
                _uiState.update { it.copy(isLoading = true) }
                val isPaymentSuccessful = paymentsRepository.makePayment(...)

                // The event of what to do when the payment response comes back
                // is immediately handled here. It causes a UI state update.
                _uiState.update {
                    it.copy(
                        isLoading = false,
                        paymentResult = PaymentResult(it.paymentInfo, isPaymentSuccessful)
                    )
                }
            } catch (ioe: IOException) { ... }
            finally { makePaymentJob = null }
        }
    }
}