class SimpleEmailService implements EmailService {

    @Override
    public CompletableFuture<Set<String>> sendSimpleEmail(String subject, String message, String... userEmails) {
        String htmlBody = emailTemplate.substring(emailTemplate.indexOf(BODY_BINDING) + BODY_BINDING.length(),
                emailTemplate.lastIndexOf(BODY_BINDING));
        htmlBody = htmlBody.replace(MESSAGE_BINDING, message);
        return sendEmail(subject, htmlBody, userEmails);
    }

}