myCRED Points for correct answers

add_shortcode( 'points_for_correct_answer', 'render_points_for_correct_answer' );
function render_points_for_correct_answer( $atts = array(), $content = NULL ) {
    extract( shortcode_atts( array(
        'answer'   => '',
        'amount'   => '',
        'ok_text'  => '',
        'ok_img'   => '',
        'bad_text' => '',
        'bad_img'  => ''
    ), $atts ) );

    // User must be logged in
    if ( ! is_user_logged_in() || ! function_exists( 'mycred_get_settings' ) ) return;

    // Prep
    $user_id = get_current_user_id();
    $post_id = $GLOBALS['post']->ID;

    // Load myCRED
    $mycred = mycred_get_settings();

    // Answer must be set and so does the amount!
    if ( empty( $answer ) || empty( $amount ) ) return;

    // Check if form has been submitted
    if ( isset( $_POST['token'] ) && wp_verify_nonce( $_POST['token'], 'answering-question' ) ) {

        $given_answer = sanitize_text_field( $_POST['answer'] );

        if ( $given_answer == $answer ) {
            // Data
            $data = array(
                'ref_type' => 'post',
                'answer'   => $answer
            );

            // Make this unique
            if ( $mycred->has_entry( 'answer_questions', $post_id, $user_id, $data ) )
                    return 'You have already received points for this question.';

            // Add points
            $mycred->add_creds(
                'answer_questions',
                $user_id,
                $amount,
                '%plural% for correct answer on post %link_with_title%',
                $post_id,
                $data
            );

            $output = $ok_text;

            if ( ! empty( $ok_img ) )
                $output .= '<img src="' . $ok_img . '" alt="" />';

            return $output;
        }
        else {
            $output = $bad_text;

            if ( ! empty( $bad_image ) )
                $output .= '<img src="' . $bad_image . '" alt="" />';

            return $output;
        }
    }
    // No form submission
    else {

        return '
<form action="" method="post">
    <label>Answer</label>
    <input type="text" name="answer" id="answer" value="" />
    <input type="hidden" name="token" value="' . wp_create_nonce( 'answering-question' ) . '" />
    <input type="submit" name="submit" value="Send" />
</form>';

    }
}
endif;