WordPress custom taxonomy breadcrumbs based on deepest term.

taxonomy-breadcrumbs.php

<?php
if( !function_exists( 'inspiry_get_breadcrumbs_items' ) ) :
    /**
     * Returns a array of breadcrumbs items
     *
     * @param $post_id  int Post id
     * @param $breadcrumbs_taxonomy string Taxonomy name
     * @return mixed|void
     */
    function inspiry_get_breadcrumbs_items( $post_id, $breadcrumbs_taxonomy ) {

        // Add home at the beginning of the breadcrumbs
		$inspiry_breadcrumbs_items = array(
            array(
                'name' => __( 'Home', 'inspiry' ),
                'url' => esc_url( home_url('/') ),
                'class' => '',
            )
        );

        // Get all assigned terms
        $the_terms = get_the_terms( $post_id, $breadcrumbs_taxonomy );

        if ( $the_terms && ! is_wp_error( $the_terms ) ) :

            $deepest_term = $the_terms[0];
            $deepest_depth = 0;

            // Find the deepest term
            foreach( $the_terms as $term ) {
                $current_term_depth = inspiry_get_term_depth( $term->term_id, $breadcrumbs_taxonomy );
                if ( $current_term_depth > $deepest_depth ) {
                    $deepest_depth = $current_term_depth;
                    $deepest_term = $term;
                }
            }

            // work on deepest term
            if ( $deepest_term ) {

                // Get ancestors if any and add them to breadcrumbs items
                $deepest_term_ancestors = get_ancestors( $deepest_term->term_id, $breadcrumbs_taxonomy );
                if ( $deepest_term_ancestors && ( 0 < count( $deepest_term_ancestors ) ) ) {
                    $deepest_term_ancestors = array_reverse( $deepest_term_ancestors ); // reversing the array is important
                    foreach ( $deepest_term_ancestors as $term_ancestor_id ) {
                        $ancestor_term = get_term_by( 'id', $term_ancestor_id, $breadcrumbs_taxonomy );
                        $inspiry_breadcrumbs_items[] = array(
                            'name' => $ancestor_term->name,
                            'url' => get_term_link( $ancestor_term, $breadcrumbs_taxonomy ),
                            'class' => ''
                        );
                    }
                }

                // add deepest term
                $inspiry_breadcrumbs_items[] = array(
                    'name' => $deepest_term->name,
                    'url' => get_term_link( $deepest_term, $breadcrumbs_taxonomy ),
                    'class' => ''
                );

            }

        endif;

        // Add the current page / property
        $inspiry_breadcrumbs_items[] = array(
            'name' => get_the_title( $post_id ),
            'url' => '',
            'class' => 'active',
        );
		
		return apply_filters( 'inspiry_breadcrumbs_items', $inspiry_breadcrumbs_items );

	}

endif;


if( !function_exists( 'inspiry_get_term_depth' ) ) :
    /**
     * Returns an integer value that tells the term depth in it's hierarchy
     *
     * @param $term_id
     * @param $term_taxonomy
     * @return int
     */
    function inspiry_get_term_depth( $term_id, $term_taxonomy ) {
        $term_ancestors = get_ancestors( $term_id, $term_taxonomy );
        if ( $term_ancestors ) {
            return count( $term_ancestors );
        }
        return 0;
    }
endif;

usage-example.php

<?php
/**
 * Projects breadcrumb
 *
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

//source: https://gist.github.com/saqibsarwar/471cb91a6b17ffc457e2
	global $post;
	$inspiry_breadcrumbs_items = inspiry_get_breadcrumbs_items( $post->ID, 'project-category');
	$projects_page = get_option( 'projects-pages-fields' );
	mz_pr(get_option( 'projects-pages-fields' )['projects_page_id']);
	if ( is_array( $inspiry_breadcrumbs_items ) && ( 0 < count( $inspiry_breadcrumbs_items ) ) ) {
		?>
		<nav class="projects-breadcrumb">
			<?php
			foreach( $inspiry_breadcrumbs_items as $item ) :
				$class = ( !empty( $item['class'] ) ) ? 'class="' . $item['class'] . '"' : '';
				if ( !empty ( $item['url'] ) ) :
					?>
						<a href="<?php echo esc_url( $item['url'] ); ?>" <?php echo $class ?>><?php echo $item['name']; ?></a>   
						<?php if (get_queried_object()->name === $item['name']) { ?>
	   </nav>
						<?php
							break; 
						}
						?>                    
						<span class="breadcrumb-separator"> / </span>
					<?php
				else :
					?>
					<?php echo $item['name']; ?>
					<?php
				endif;
			endforeach;
			?>
		</nav>
		<?php
	}
?>
<br style="clear: both;" />