gistfile1.txt

        final Parameter.Key<CraftCurrency> currencyKey = Parameter.key("currency", CraftCurrency.class);
        final Parameter.Value<CraftCurrency> currencyPara = Parameter.builder(CraftCurrency.class)
                .key(currencyKey)
                .addParser(new CraftCurrencyParser())
                .completer(new CraftCurrencyParser.CraftCurrencyCompleter())
                .build();
                
        final Command.Parameterized bal = Command.builder()
                .addParameter(userPara)
                .addParameter(currencyPara)
                .executor(context -> {
                    CraftEcoService service = Main.instance.getCraftEcoService();
                    Audience audience = (Audience) context.cause().root();
                    service.findOrCreateAccount(context.requireOne(userPara)).ifPresent(acc -> {
                        audience.sendMessage(Util.toComponent(acc.balance(context.one(currencyKey).orElse(((CraftCurrency) service.defaultCurrency()))).toString()));
                    });
                    return CommandResult.success();
                })
                .build();
                
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class CraftCurrencyParser implements ValueParser<CraftCurrency> {

    @Override
    public Optional<? extends CraftCurrency> parseValue(Parameter.Key<? super CraftCurrency> parameterKey, ArgumentReader.Mutable reader, CommandContext.Builder context) throws ArgumentParseException {
        String currencyName = reader.peekString();
        for (CraftCurrency currency : ConfigLoader.instance.getConfig().currencies) {
            if (Util.toPlain(currency.displayName()).equalsIgnoreCase(currencyName)){
                return Optional.of(currency);
            }
        }
        return Optional.empty();
    }

    public static class CraftCurrencyCompleter implements ValueCompleter {

        @Override
        public List<CommandCompletion> complete(CommandContext context, String currentInput) {
            return ConfigLoader.instance.getConfig().currencies.stream()
                    .map(cur -> CommandCompletion.of(Util.toPlain(cur.displayName())))
                    .collect(Collectors.toList());
        }
    }
}
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