function save_index( $post_id ) {
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
        return;
    }

    $slug   = 'post';
    $letter = '';

    // only run for posts
    if ( isset( $_POST['post_type'] ) && ( $slug != $_POST['post_type'] ) ) {
        return;
    }

    // Check user capabilities
    if ( ! current_user_can( 'edit_post', $post_id ) ) {
        return;
    }

    $taxonomy = 'index'; // our custom taxonomy

    if ( isset( $_POST['post_type'] ) ) {

        // Get the title of the post
        $title = strtolower( $_POST['post_title'] );

        // The next few lines remove A, An, or The from the start of the title
        $splitTitle    = explode( ' ', $title );
        $blacklist     = [ 'an ', 'a ', 'the ' ];
        $splitTitle[0] = str_replace( $blacklist, '', strtolower( $splitTitle[0] ) );
        $title         = implode( ' ', $splitTitle );

        // Get the first letter of the title
        $letter = substr( $title, 0, 1 );

        // Set to 0-9 if it's a number
        if ( is_numeric( $letter ) ) {
            $letter = '0-9';
        }
    }

    // set term as first letter of post title, lower case
    wp_set_post_terms( $post_id, $letter, $taxonomy );
}

add_action( 'save_post', 'save_index' );

add_action( 'init', function () {

    add_rewrite_tag( '%filter%', '([^&]+)' );
    add_rewrite_rule( 'member/filter/([a-zA-Z0-9-]{1,3})[/]?$', 'index.php?post_type=mbe-members&filter=$matches[1]', 'top' );

} );

$filter       = get_query_var( 'filter' );
$filter_start = null;
$filter_end   = null;

if ( strpos( $filter, '-' ) !== false ) {

    if ( $pieces = explode( '-', $filter ) ) {

        if ( isset( $pieces[0] ) ) {
            $filter_start = $pieces[0];
        }

        if ( isset( $pieces[1] ) ) {
            $filter_end = $pieces[1];
        }

    }

} else {
    $filter_start = substr( $filter, 0, 1 );
}

global $wpdb;

$post_ids = array();

if ( ! is_null( $filter_start ) && ! is_null( $filter_end ) ) {

    $range = range( $filter_start, $filter_end );

    foreach ( $range as $value ) {

        $query_args = array(
            'SELECT' => 'ID',
            'FROM'   => $wpdb->posts,
            'WHERE'  => 'post_title'
        );

        if ( is_numeric( $value ) ) {
            $query_args['LIKE'] = '%d';
        } else {
            $query_args['LIKE'] = '%s';
        }

        if ( $query = $wpdb->get_results( $wpdb->prepare( "
            SELECT {$query_args['SELECT']}
            FROM {$query_args['FROM']}
            WHERE {$query_args['WHERE']}
            LIKE {$query_args['LIKE']}
            ", "{$value}%" ) ) ) {

            foreach ( $query as $result ) {
                $post_ids[] = $result->ID;
            }

        }

    }

} else {

    if ( ! is_null( $filter_start ) ) {

        $value = $filter_start;

        $query_args = array(
            'SELECT' => 'ID',
            'FROM'   => $wpdb->posts,
            'WHERE'  => 'post_title',
        );

        if ( is_numeric( $value ) ) {
            $query_args['LIKE'] = '%d';
        } else {
            $query_args['LIKE'] = '%s';
        }

        if ( $query = $wpdb->get_results( $wpdb->prepare( "
            SELECT {$query_args['SELECT']}
            FROM {$query_args['FROM']}
            WHERE {$query_args['WHERE']}
            LIKE {$query_args['LIKE']}
            ", "{$value}%" ) ) ) {

            foreach ( $query as $result ) {
                $post_ids[] = $result->ID;
            }

        }

    }

}

$content = '';

if ( ! empty( $post_ids ) ) {

    $query = new WP_Query( array(
        'post_type'              => 'mbe-members',
        'posts_per_page'         => 100,
        'post_status'            => 'publish',
        'orderby'                => 'post_title',
        'order'                  => 'ASC',
        'update_post_meta_cache' => false,
        'update_post_term_cache' => false,
        'suppress_filters'       => true,
        'post__in'               => $post_ids
    ) );

    if ( $query->have_posts() ) {

        foreach ( $query->posts as $post ) {
            $content .= $post->post_title . '<br />';
        }

    }

}

echo '<div>' . PHP_EOL;

echo '<ul class="nav nav-tabs" role="tablist">' . PHP_EOL;

$class = '';

if ( $filter == '0-9' ) {
    $class = 'active';
}

echo '<li role="presentation" class="' . $class . '"><a href="' . site_url( '/member/filter/0-9/' ) . '" aria-controls="0-9" role="tab">0-9</a></li>' . PHP_EOL;

foreach ( range( 'a', 'z' ) as $letter ) {

    $class = '';

    if ( $letter == $filter_start ) {
        $class = 'active';
    }

    echo '<li role="presentation" class="' . $class . '"><a href="' . site_url( '/member/filter/' . $letter . '/' ) . '" aria-controls="' . $letter . '" role="tab">' . $letter . '</a></li>' . PHP_EOL;

}

echo '</ul>' . PHP_EOL;

echo '<div class="tab-content">' . PHP_EOL;

$class = '';

if ( $filter == '0-9' ) {
    $class = 'active';
}

echo '<div role="tabpanel" class="tab-pane ' . $class . '" id="0-9">' . PHP_EOL;

if ( $filter == '0-9' ) {
    echo $content;
}

echo '</div>' . PHP_EOL;

foreach ( range( 'a', 'z' ) as $letter ) {

    $class = '';

    if ( $letter == $filter_start ) {
        $class = 'active';
    }

    echo '<div role="tabpanel" class="tab-pane ' . $class . '" id="' . $letter . '">' . PHP_EOL;

    if ( $letter == $filter_start ) {
        echo $content;
    }

    echo '</div>' . PHP_EOL;

}

echo '</div>' . PHP_EOL;

echo '</div>' . PHP_EOL;