Add product category tree sidebar to archive and single product pages (v0.1.7)

Hierarchical category navigation with collapsible sub-levels up to 3 levels
deep, using Bootstrap 5 list-group and collapse components. Sidebar renders
on both archive/shop and single product pages with responsive offcanvas on
mobile. Active category highlighting and ancestor auto-expand for intuitive
navigation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions.php

@@ -293,6 +293,91 @@ function wc_bootstrap_loop_columns(): int {
 }
 add_filter( 'loop_shop_columns', 'wc_bootstrap_loop_columns' );
 
+/**
+ * Build a hierarchical product category tree up to a given depth.
+ *
+ * Returns a nested array of category objects with children, suitable for
+ * rendering a multi-level navigation sidebar. Each node contains the
+ * WP_Term object plus a 'children' array and an 'is_active'/'is_ancestor'
+ * flag based on the current query.
+ *
+ * @since 0.1.7
+ *
+ * @param int $max_depth Maximum nesting depth (1 = top-level only, 3 = three levels).
+ * @return array Hierarchical category tree.
+ */
+function wc_bootstrap_get_category_tree( int $max_depth = 3 ): array {
+    $terms = get_terms( [
+        'taxonomy'   => 'product_cat',
+        'hide_empty' => true,
+        'orderby'    => 'name',
+        'order'      => 'ASC',
+    ] );
+
+    if ( is_wp_error( $terms ) || empty( $terms ) ) {
+        return [];
+    }
+
+    // Determine the currently viewed category (if any).
+    $current_term_id = 0;
+    $ancestor_ids    = [];
+
+    if ( is_product_category() ) {
+        $queried = get_queried_object();
+        if ( $queried instanceof \WP_Term ) {
+            $current_term_id = $queried->term_id;
+            $ancestor_ids    = get_ancestors( $current_term_id, 'product_cat', 'taxonomy' );
+        }
+    } elseif ( is_product() ) {
+        // On single product pages, highlight the first assigned category.
+        global $product;
+        if ( $product ) {
+            $cat_ids = $product->get_category_ids();
+            if ( ! empty( $cat_ids ) ) {
+                $current_term_id = $cat_ids[0];
+                $ancestor_ids    = get_ancestors( $current_term_id, 'product_cat', 'taxonomy' );
+            }
+        }
+    }
+
+    // Index terms by parent for efficient tree building.
+    $by_parent = [];
+    foreach ( $terms as $term ) {
+        $by_parent[ $term->parent ][] = $term;
+    }
+
+    /**
+     * Recursively build tree nodes from the parent-indexed map.
+     */
+    $build = function ( int $parent_id, int $depth ) use ( &$build, $by_parent, $max_depth, $current_term_id, $ancestor_ids ): array {
+        if ( $depth > $max_depth || ! isset( $by_parent[ $parent_id ] ) ) {
+            return [];
+        }
+
+        $nodes = [];
+        foreach ( $by_parent[ $parent_id ] as $term ) {
+            $children    = $build( $term->term_id, $depth + 1 );
+            $is_active   = ( $term->term_id === $current_term_id );
+            $is_ancestor = in_array( $term->term_id, $ancestor_ids, true );
+
+            $nodes[] = [
+                'term_id'     => $term->term_id,
+                'name'        => $term->name,
+                'slug'        => $term->slug,
+                'count'       => $term->count,
+                'url'         => get_term_link( $term ),
+                'is_active'   => $is_active,
+                'is_ancestor' => $is_ancestor,
+                'children'    => $children,
+            ];
+        }
+
+        return $nodes;
+    };
+
+    return $build( 0, 1 );
+}
+
 /**
  * Remove WooCommerce's default sidebar hook.
  *