class ServerConfigsValidator implements ConstraintValidator<ValidServerConfigs, Config> {

    @Override
    public boolean isValid(Config config, ConstraintValidatorContext constraintContext) {
        // Note that null serverConfigs are actually prevented by `@ValidEitherServerConfigsOrServer` in Config
        if (null == config || config.isServerConfigsNull()) {
            return true;
        }

        final Map<AppType, Integer> counts =
                config.getServerConfigs().stream()
                        .collect(Collectors.toMap(ServerConfig::getApp, v -> 1, (l, r) -> l + 1));

        final int p2PEnabledConfigsCount = counts.getOrDefault(AppType.P2P, 0);
        final int q2TEnabledConfigsCount = counts.getOrDefault(AppType.Q2T, 0);

        if (p2PEnabledConfigsCount != 1) {
            LOGGER.debug("Exactly one P2P server must be configured.");
            constraintContext.disableDefaultConstraintViolation();
            constraintContext
                    .buildConstraintViolationWithTemplate("Exactly one P2P server must be configured.")
                    .addConstraintViolation();
            return false;
        }

        if (config.isBootstrapNode()) {
            if (q2TEnabledConfigsCount != 0) {
                LOGGER.debug("Q2T server cannot be specified on a bootstrap node.");
                constraintContext.disableDefaultConstraintViolation();
                constraintContext
                        .buildConstraintViolationWithTemplate("Q2T server cannot be specified on a bootstrap node.")
                        .addConstraintViolation();
                return false;
            }
        } else if (q2TEnabledConfigsCount == 0) {
            LOGGER.debug("At least one Q2T server must be configured or bootstrap mode enabled.");
            constraintContext.disableDefaultConstraintViolation();
            constraintContext
                    .buildConstraintViolationWithTemplate(
                            "At least one Q2T server must be configured or bootstrap mode enabled.")
                    .addConstraintViolation();
            return false;
        }

        return true;
    }

}