Random Posts Shortcode

// How long the list of posts to pick from is cached, in minutes.
$wpide_random_posts_cache_minutes = 60;

// How many of the newest posts the random picks come from.
$wpide_random_posts_pool_size = 200;

add_shortcode( 'random_posts', function ( $atts ) use ( $wpide_random_posts_cache_minutes, $wpide_random_posts_pool_size ) {
    $atts = shortcode_atts( array(
        'count'     => 5,
        'post_type' => 'post',
        'category'  => '',
    ), $atts, 'random_posts' );

    $count     = max( 1, min( 50, absint( $atts['count'] ) ) );
    $post_type = sanitize_key( $atts['post_type'] );

    if ( ! post_type_exists( $post_type ) || ! is_post_type_viewable( $post_type ) ) {
        return '';
    }

    $query = array(
        'post_type'           => $post_type,
        'post_status'         => 'publish',
        'posts_per_page'      => max( $count, (int) $wpide_random_posts_pool_size ),
        'fields'              => 'ids',
        'has_password'        => false,
        'ignore_sticky_posts' => true,
        'no_found_rows'       => true,
        'orderby'             => 'date',
        'order'               => 'DESC',
    );

    // category="news" or category="news,12" (slugs or IDs).
    $categories = array_filter( array_map( 'trim', explode( ',', (string) $atts['category'] ) ) );

    if ( $categories && is_object_in_taxonomy( $post_type, 'category' ) ) {
        $ids   = array_map( 'intval', array_filter( $categories, 'ctype_digit' ) );
        $slugs = array_map( 'sanitize_title', array_diff( $categories, array_filter( $categories, 'ctype_digit' ) ) );

        $query['tax_query'] = array( 'relation' => 'OR' );

        if ( $ids ) {
            $query['tax_query'][] = array( 'taxonomy' => 'category', 'field' => 'term_id', 'terms' => $ids );
        }

        if ( $slugs ) {
            $query['tax_query'][] = array( 'taxonomy' => 'category', 'field' => 'slug', 'terms' => array_values( $slugs ) );
        }
    }

    // The candidate list is cached, so pages do not run a slow ORDER BY RAND() query.
    $cache_key = 'wpide_random_posts_' . md5( (string) wp_json_encode( $query ) );
    $pool      = get_transient( $cache_key );

    if ( ! is_array( $pool ) ) {
        $pool = array_map( 'intval', get_posts( $query ) );
        set_transient( $cache_key, $pool, max( 1, (int) $wpide_random_posts_cache_minutes ) * MINUTE_IN_SECONDS );
    }

    if ( is_singular() ) {
        $pool = array_diff( $pool, array( get_queried_object_id() ) );
    }

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

    shuffle( $pool );

    $posts = get_posts( array(
        'post__in'       => array_slice( $pool, 0, $count ),
        'post_type'      => $post_type,
        'posts_per_page' => $count,
        'orderby'        => 'post__in',
    ) );

    $items = '';

    foreach ( $posts as $post ) {
        $items .= '<li><a href="' . esc_url( get_permalink( $post ) ) . '">' . esc_html( get_the_title( $post ) ) . '</a></li>';
    }

    return '' === $items ? '' : '<ul class="wpide-random-posts">' . $items . '</ul>';
} );