WordPress Schema.org breadcrumbs without a plugin

WP Schema.org Breadcrumbs without Plugin

function wordpress_breadcrumbs()
{
    // Set variables for later use
    $here_text        = __( 'You are currently here' );
    $home_link        = home_url('/');
    $home_text        = __( 'Home' );
    $link_before      = '<span itemprop="itemListElement" itemscope itemtype="http://schema.org/ListItem">';
    $link_after       = '<meta itemprop="position" content="2" /></span>';
    $link_attr        = ' itemprop="item"';
    $link             = $link_before . '<span itemprop="name"><a' . $link_attr . ' href="%1$s">%2$s</a></span>' . $link_after;
    $delimiter        = '&nbsp;&sol;&nbsp;';              // Delimiter between crumbs
    $before           = '<span class="current">'; // Tag before the current crumb
    $after            = '</span>';                // Tag after the current crumb
    $page_addon       = '';                       // Adds the page number if the query is paged
    $breadcrumb_trail = '';
    $category_links   = '';

    /** 
     * Set our own $wp_the_query variable. Do not use the global variable version due to 
     * reliability
     */
    $wp_the_query   = $GLOBALS['wp_the_query'];
    $queried_object = $wp_the_query->get_queried_object();

    // Handle single post requests which includes single pages, posts and attatchments
    if ( is_singular() ) 
    {
        /** 
         * Set our own $post variable. Do not use the global variable version due to 
         * reliability. We will set $post_object variable to $GLOBALS['wp_the_query']
         */
        $post_object = sanitize_post( $queried_object );

        // Set variables 
        $title          = apply_filters( 'the_title', $post_object->post_title );
        $parent         = $post_object->post_parent;
        $post_type      = $post_object->post_type;
        $post_id        = $post_object->ID;
        $post_link      = $before . $title . $after;
        $parent_string  = '';
        $post_type_link = '';

        if ( 'post' === $post_type ) 
        {
            // Get the post categories
            $categories = get_the_category( $post_id );
            if ( $categories ) {
                // Lets grab the first category
                $category  = $categories[0];

                $category_links = get_category_parents( $category, true, $delimiter );
                $category_links = str_replace( '<a',   $link_before . '<a' . $link_attr, $category_links );
                $category_links = str_replace( '</a>', '</a>' . $link_after,             $category_links );
            }
        }

        if ( !in_array( $post_type, ['post', 'page', 'attachment'] ) )
        {
            $post_type_object = get_post_type_object( $post_type );
            $archive_link     = esc_url( get_post_type_archive_link( $post_type ) );

            $post_type_link   = sprintf( $link, $archive_link, $post_type_object->labels->singular_name );
        }

        // Get post parents if $parent !== 0
        if ( 0 !== $parent ) 
        {
            $parent_links = [];
            while ( $parent ) {
                $post_parent = get_post( $parent );

                $parent_links[] = sprintf( $link, esc_url( get_permalink( $post_parent->ID ) ), get_the_title( $post_parent->ID ) );

                $parent = $post_parent->post_parent;
            }

            $parent_links = array_reverse( $parent_links );

            $parent_string = implode( $delimiter, $parent_links );
        }

        // Lets build the breadcrumb trail
        if ( $parent_string ) {
            $breadcrumb_trail = $parent_string . $delimiter . $post_link;
        } else {
            $breadcrumb_trail = $post_link;
        }

        if ( $post_type_link )
            $breadcrumb_trail = $post_type_link . $delimiter . $breadcrumb_trail;

        if ( $category_links )
            $breadcrumb_trail = $category_links . $breadcrumb_trail;
    }

    // Handle archives which includes category-, tag-, taxonomy-, date-, custom post type archives and author archives
    if( is_archive() )
    {
        if (    is_category()
             || is_tag()
             || is_tax()
        ) {
            // Set the variables for this section
            $term_object        = get_term( $queried_object );
            $taxonomy           = $term_object->taxonomy;
            $term_id            = $term_object->term_id;
            $term_name          = $term_object->name;
            $term_parent        = $term_object->parent;
            $taxonomy_object    = get_taxonomy( $taxonomy );
            $current_term_link  = $before . $taxonomy_object->labels->singular_name . ': ' . $term_name . $after;
            $parent_term_string = '';

            if ( 0 !== $term_parent )
            {
                // Get all the current term ancestors
                $parent_term_links = [];
                while ( $term_parent ) {
                    $term = get_term( $term_parent, $taxonomy );

                    $parent_term_links[] = sprintf( $link, esc_url( get_term_link( $term ) ), $term->name );

                    $term_parent = $term->parent;
                }

                $parent_term_links  = array_reverse( $parent_term_links );
                $parent_term_string = implode( $delimiter, $parent_term_links );
            }

            if ( $parent_term_string ) {
                $breadcrumb_trail = $parent_term_string . $delimiter . $current_term_link;
            } else {
                $breadcrumb_trail = $current_term_link;
            }

        } elseif ( is_author() ) {

            $breadcrumb_trail = __( 'Author archive for ') .  $before . $queried_object->data->display_name . $after;

        } elseif ( is_date() ) {
            // Set default variables
            $year     = $wp_the_query->query_vars['year'];
            $monthnum = $wp_the_query->query_vars['monthnum'];
            $day      = $wp_the_query->query_vars['day'];

            // Get the month name if $monthnum has a value
            if ( $monthnum ) {
                $date_time  = DateTime::createFromFormat( '!m', $monthnum );
                $month_name = $date_time->format( 'F' );
            }

            if ( is_year() ) {

                $breadcrumb_trail = $before . $year . $after;

            } elseif( is_month() ) {

                $year_link        = sprintf( $link, esc_url( get_year_link( $year ) ), $year );

                $breadcrumb_trail = $year_link . $delimiter . $before . $month_name . $after;

            } elseif( is_day() ) {

                $year_link        = sprintf( $link, esc_url( get_year_link( $year ) ),             $year       );
                $month_link       = sprintf( $link, esc_url( get_month_link( $year, $monthnum ) ), $month_name );

                $breadcrumb_trail = $year_link . $delimiter . $month_link . $delimiter . $before . $day . $after;
            }

        } elseif ( is_post_type_archive() ) {

            $post_type        = $wp_the_query->query_vars['post_type'];
            $post_type_object = get_post_type_object( $post_type );

            $breadcrumb_trail = $before . $post_type_object->labels->singular_name . $after;

        }
    }   

    // Handle the search page
    if ( is_search() ) {
        $breadcrumb_trail = __( 'Search query for: ' ) . $before . get_search_query() . $after;
    }

    // Handle 404's
    if ( is_404() ) {
        $breadcrumb_trail = $before . __( 'Error 404' ) . $after;
    }

    // Handle paged pages
    if ( is_paged() ) {
        $current_page = get_query_var( 'paged' ) ? get_query_var( 'paged' ) : get_query_var( 'page' );
        $page_addon   = $before . sprintf( __( ' ( Page %s )' ), number_format_i18n( $current_page ) ) . $after;
    }

    $breadcrumb_output_link  = '';
    $breadcrumb_output_link .= '<div class="breadcrumb" itemscope itemtype="http://schema.org/BreadcrumbList">';
    if ( is_home() || is_front_page() ) {
        // Do not show breadcrumbs on page one of home and frontpage
        if ( is_paged() ) {
            $breadcrumb_output_link .= $here_text . $delimiter;
            $breadcrumb_output_link .= '<a href="' . $home_link . '">' . $home_text . '</a>';
            $breadcrumb_output_link .= $page_addon;
        }
    } else {
        $breadcrumb_output_link .= $here_text . $delimiter;
        $breadcrumb_output_link .= '<span itemprop="itemListElement" itemscope="" itemtype="http://schema.org/ListItem"><a href="' . $home_link . '" itemprop="item"><span itemprop="name">' . $home_text . '</span></a><meta itemprop="position" content="1" /></span>';
        $breadcrumb_output_link .= $delimiter;
        $breadcrumb_output_link .= $breadcrumb_trail;
        $breadcrumb_output_link .= $page_addon;
    }
    $breadcrumb_output_link .= '</div><!-- .breadcrumb -->';

    return $breadcrumb_output_link;
}

It works really fine. But there is one small issue with <meta itemprop="position" />. The value of the attribute "content" is always "2". It would be great to change it with sprintf but the numbers go backwards. So, eventually I've decided to do it by explode.

So, I've changed <meta itemprop="position" content="2" /> to <meta itemprop="position" content="*$*" />

And before return:

    $db_breadcrumb_parts = explode( '*$*', $breadcrumb_output_link );
    $i = 0;
    $breadcrumb_output_link = $db_breadcrumb_parts[ $i ];
    while ( $db_breadcrumb_parts[ ++$i ] )
        $breadcrumb_output_link .= $i . $db_breadcrumb_parts[ $i ];

I don't think that it is the best solution for your function. You can also take my idea if you want. But if you have a better idea, let me know.