WordPress theme snippet to warn if no permalink structure configured

functions.php

<?php
/**
 * "We strongly recommend a permalink structure" admin site notice
 *
 * from http://wordpress.stackexchange.com/a/157071/3276
 */

if ( is_admin() && ( ! defined( 'DOING_AJAX' ) || ! DOING_AJAX ) ) {
    /* Admin-site only code */

    /**
     * If we don't have a permalink structure configured, and if the user has
     * permission to configure one, display a warning at the top of the admin
     * site. (We can't yet test which screen we're on.)
     */
    if ( ( '' == get_option( 'permalink_structure' ) ) &&
         current_user_can( 'manage_options' ) ) {
        /**
         * If we're not already on the permalink configuration page, display a
         * warning recommending the administrator configure one.
         */
        function wpse_157069_permalink_warning() {
            $screen = get_current_screen();
            if ( ! isset( $screen ) || ( 'options-permalink' != $screen->id ) ) {
                echo '<div id="permalink_warning" class="error">';
                echo '<p>' . sprintf(
                     __( 'We strongly recommend adding a %s to your site when using WPSE AwesomeTheme.' ),
                     sprintf( '<a href="%s">%s</a>', esc_url( admin_url( 'options-permalink.php' ) ),
                         __( 'permalink structure' ) ) ) . '</p>';
                echo '</div>';
            }
        }
        add_action( 'admin_footer', 'wpse_157069_permalink_warning' );
    }
}