WooPack - Product Categories - Multi-level filters

code.php

<?php

// Please copy the code below and paste it to your current theme's functions.php

add_filter('pp_category_grid_query_args', function($args, $settings) {
	if ( is_tax() || is_category() || is_tag() ) {
	   $current_object = get_queried_object();
	   	$taxonomy = $current_object->taxonomy;

		// Unset or remove variables.
	  if ( isset( $args['parent'] ) ) {
				unset( $args['parent'] );
	  }
		if ( isset( $args['exclude'] ) ) {
			unset( $args['exclude'] );
	  }
		if ( isset( $args['child_of'] ) ) {
			unset( $args['child_of'] );
	  }

		// Show only top level subcategories of current category
	  if ( 'default' === $settings->display_data && 'children_only' === $settings->on_tax_archive ) {
		   $args['parent'] = array( '', $current_object->term_id );
	  }

		// Show all subcategories of current category.
	  if ( 'parent_only' === $settings->display_data && 'children_only' === $settings->on_tax_archive ) {
			$args['child_of'] = $current_object->term_id;
		}

		// Show only children categories of top level subcategories of current category.
		if ( 'children_only' === $settings->display_data && 'children_only' === $settings->on_tax_archive ) {
			$args['child_of'] = $current_object->term_id;
			$args['parent'] = $current_object->term_id;
			$top_level_children = get_categories( $args );
			$subchild_top_level = array('');

			if ( ! is_wp_error( $top_level_children ) && count( $top_level_children ) ) {
				foreach ( $top_level_children as $top_level_child ) {
					$children = get_term_children( $top_level_child->term_id, $taxonomy );
					if ( ! is_wp_error( $children ) && count( $children ) ) {
						$subchild_top_level = array_merge( $subchild_top_level, $children );
					}
				}
			}
			if ( ! empty( $subchild_top_level ) ) {
				unset( $args['child_of'] );
				unset( $args['parent'] );
				$args['include'] = $subchild_top_level;
			}
		}
	}
	return $args;
}, 10, 2);