MakePaymentViewModel.kt

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

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

    val uiState: StateFlow<MakePaymentUiState> = /* ... */

    // ⚠️⚠️ DO NOT DO THIS!! ⚠️⚠️
    // This one-off ViewModel event hasn't been handled nor reduced to state
    // Boolean represents whether or not the payment was successful
    private val _navigateToPaymentResultScreen = Channel<Boolean>()

    // `receiveAsFlow` makes sure only one collector will process each
    // navigation event to avoid multiple back stack entries
    val navigateToPaymentResultScreen = _navigateToPaymentResultScreen.receiveAsFlow()

    // 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) } // Show loading spinner
                val isPaymentSuccessful = paymentsRepository.makePayment(...)
                _navigateToPaymentResultScreen.send(isPaymentSuccessful)
            } catch (ioe: IOException) { ... }
            finally { makePaymentJob = null }
        }
    }
}