Display an External RSS Feed With a Shortcode

add_shortcode( 'rss_feed', function ( $atts ) {
    $atts = shortcode_atts( array(
        'url'          => '',
        'items'        => 5,
        'show_date'    => 'yes',
        'show_summary' => 'no',
    ), $atts, 'rss_feed' );

    $url = esc_url_raw( $atts['url'] );

    if ( ! $url ) {
        return '';
    }

    include_once ABSPATH . WPINC . '/feed.php';

    $feed = fetch_feed( $url );

    if ( is_wp_error( $feed ) ) {
        return current_user_can( 'edit_posts' ) ? '<p class="wpide-rss-error">Feed could not be loaded: ' . esc_html( $feed->get_error_message() ) . '</p>' : '';
    }

    $items = $feed->get_items( 0, min( 20, max( 1, absint( $atts['items'] ) ) ) );

    if ( ! $items ) {
        return '';
    }

    $html = '<ul class="wpide-rss-feed">';

    foreach ( $items as $item ) {
        $html .= '<li><a href="' . esc_url( $item->get_permalink() ) . '" rel="noopener">' . esc_html( wp_strip_all_tags( (string) $item->get_title() ) ) . '</a>';

        if ( 'yes' === $atts['show_date'] && $item->get_date( 'U' ) ) {
            $html .= ' <time datetime="' . esc_attr( gmdate( 'c', (int) $item->get_date( 'U' ) ) ) . '">' . esc_html( wp_date( get_option( 'date_format' ), (int) $item->get_date( 'U' ) ) ) . '</time>';
        }

        if ( 'yes' === $atts['show_summary'] ) {
            $html .= '<p>' . esc_html( wp_trim_words( wp_strip_all_tags( (string) $item->get_description() ), 30 ) ) . '</p>';
        }

        $html .= '</li>';
    }

    return $html . '</ul>';
} );