Balance Alerts Generator

public static List<KeyValue<SpecificRecord, OutboundMessage>> generateAlerts(AccountEntry accountEntry,
                                                                                 CustomerAlertSettings settings) {
        /* Generates addressed alerts for an AccountEntry, using the alert settings with the following steps:
        *  1) Settings are for a specific account, drop AccountEntries not for this account
        *  2) Match each setting with all alerts to generate appropriate messages
        *  3) Address the generated messages
        */

        if (settings == null) {
            return new ArrayList<>();
        }

        return settings.getAccountAlertSettings().stream()
                .filter(accountAlertSettings -> matchAccount(accountEntry, accountAlertSettings))
                .flatMap(accountAlertSettings -> accountAlertSettings.getSettings().stream())
                .flatMap(accountAlertSetting -> Stream.of(
                        generateBalanceAbove(accountEntry, accountAlertSetting),
                        generateBalanceBelow(accountEntry, accountAlertSetting),
                        generateCreditedAbove(accountEntry, accountAlertSetting),
                        generateDebitedAbove(accountEntry, accountAlertSetting))
                )
                .filter(Optional::isPresent).map(Optional::get)
                .flatMap(messageWithChannels -> mapAddresses(messageWithChannels.getValue0(), settings.getAddresses())
                        .map(address -> KeyValue.pair(address, messageWithChannels.getValue1())))
                .collect(toList());
    }