Migrate classic menus to block-based menus on theme switch

lib/navigation.php

@@ -571,3 +571,197 @@ function gutenberg_get_navigation_areas_paths_to_preload() {
 	}
 	return $paths;
 }
+
+/**
+ * Migrates classic menus to block-based menus on theme switch.
+ *
+ * @param string   $new_name  Name of the new theme.
+ * @param WP_Theme $new_theme New theme.
+ * @param WP_Theme $old_theme Old theme.
+ * @see switch_theme WordPress action.
+ */
+function gutenberg_migrate_nav_on_theme_switch( $new_name, $new_theme, $old_theme ) {
+	// Do nothing when switching to a theme that does not support site editor.
+	if ( ! gutenberg_experimental_is_site_editor_available() ) {
+		return;
+	}
+
+	// get_nav_menu_locations() calls get_theme_mod() which depends on the stylesheet option.
+	// At the same time, switch_theme runs only after the stylesheet option was updated to $new_theme.
+	// To retrieve theme mods of the old theme, the getter is hooked to get_option( 'stylesheet' ) so that we
+	// get the old theme, which causes the get_nav_menu_locations to get the locations of the old theme.
+	$get_old_theme_stylesheet = function() use ( $old_theme ) {
+		return $old_theme->get_stylesheet();
+	};
+	add_filter( 'option_stylesheet', $get_old_theme_stylesheet );
+
+	$locations    = get_nav_menu_locations();
+	$area_mapping = get_option( 'fse_navigation_areas', array() );
+
+	foreach ( $locations as $location_name => $menu_id ) {
+		// Get the menu from the location, skipping if there is no
+		// menu or there was an error.
+		$menu = wp_get_nav_menu_object( $menu_id );
+		if ( ! $menu || is_wp_error( $menu ) ) {
+			continue;
+		}
+
+		$menu_items = gutenberg_global_get_menu_items_at_location( $location_name );
+		if ( empty( $menu_items ) ) {
+			continue;
+		}
+
+		$post_name   = 'classic_menu_' . $menu_id;
+		$post_status = 'publish';
+
+		// Get or create to avoid creating too many wp_navigation posts.
+		$query          = new WP_Query;
+		$matching_posts = $query->query(
+			array(
+				'name'           => $post_name,
+				'post_status'    => $post_status,
+				'post_type'      => 'wp_navigation',
+				'posts_per_page' => 1,
+			)
+		);
+
+		if ( count( $matching_posts ) ) {
+			$navigation_post_id = $matching_posts[0]->ID;
+		} else {
+			$menu_items_by_parent_id = gutenberg_global_sort_menu_items_by_parent_id( $menu_items );
+			$parsed_blocks           = gutenberg_global_parse_blocks_from_menu_items( $menu_items_by_parent_id[0], $menu_items_by_parent_id );
+			$post_data               = array(
+				'post_type'    => 'wp_navigation',
+				'post_title'   => sprintf(
+					/* translators: %s: the name of the menu, e.g. "Main Menu". */
+					__( 'Classic menu: %s', 'gutenberg' ),
+					$menu->name
+				),
+				'post_name'    => $post_name,
+				'post_content' => serialize_blocks( $parsed_blocks ),
+				'post_status'  => $post_status,
+			);
+			$navigation_post_id      = wp_insert_post( $post_data );
+		}
+
+		$area_mapping[ $location_name ] = $navigation_post_id;
+	}
+	remove_filter( 'option_stylesheet', $get_old_theme_stylesheet );
+
+	update_option( 'fse_navigation_areas', $area_mapping );
+}
+
+add_action( 'switch_theme', 'gutenberg_migrate_nav_on_theme_switch', 200, 3 );
+
+// The functions below are copied over from packages/block-library/src/navigation/index.php
+// Let's figure out a better way of managing these global PHP dependencies.
+
+/**
+ * Returns the menu items for a WordPress menu location.
+ *
+ * @param string $location The menu location.
+ * @return array Menu items for the location.
+ */
+function gutenberg_global_get_menu_items_at_location( $location ) {
+	if ( empty( $location ) ) {
+		return;
+	}
+
+	// Build menu data. The following approximates the code in
+	// `wp_nav_menu()` and `gutenberg_output_block_nav_menu`.
+
+	// Find the location in the list of locations, returning early if the
+	// location can't be found.
+	$locations = get_nav_menu_locations();
+	if ( ! isset( $locations[ $location ] ) ) {
+		return;
+	}
+
+	// Get the menu from the location, returning early if there is no
+	// menu or there was an error.
+	$menu = wp_get_nav_menu_object( $locations[ $location ] );
+	if ( ! $menu || is_wp_error( $menu ) ) {
+		return;
+	}
+
+	$menu_items = wp_get_nav_menu_items( $menu->term_id, array( 'update_post_term_cache' => false ) );
+	_wp_menu_item_classes_by_context( $menu_items );
+
+	return $menu_items;
+}
+
+
+/**
+ * Sorts a standard array of menu items into a nested structure keyed by the
+ * id of the parent menu.
+ *
+ * @param array $menu_items Menu items to sort.
+ * @return array An array keyed by the id of the parent menu where each element
+ *               is an array of menu items that belong to that parent.
+ */
+function gutenberg_global_sort_menu_items_by_parent_id( $menu_items ) {
+	$sorted_menu_items = array();
+	foreach ( (array) $menu_items as $menu_item ) {
+		$sorted_menu_items[ $menu_item->menu_order ] = $menu_item;
+	}
+	unset( $menu_items, $menu_item );
+
+	$menu_items_by_parent_id = array();
+	foreach ( $sorted_menu_items as $menu_item ) {
+		$menu_items_by_parent_id[ $menu_item->menu_item_parent ][] = $menu_item;
+	}
+
+	return $menu_items_by_parent_id;
+}
+
+/**
+ * Turns menu item data into a nested array of parsed blocks
+ *
+ * @param array $menu_items               An array of menu items that represent
+ *                                        an individual level of a menu.
+ * @param array $menu_items_by_parent_id  An array keyed by the id of the
+ *                                        parent menu where each element is an
+ *                                        array of menu items that belong to
+ *                                        that parent.
+ * @return array An array of parsed block data.
+ */
+function gutenberg_global_parse_blocks_from_menu_items( $menu_items, $menu_items_by_parent_id ) {
+	if ( empty( $menu_items ) ) {
+		return array();
+	}
+
+	$blocks = array();
+
+	foreach ( $menu_items as $menu_item ) {
+		$class_name       = ! empty( $menu_item->classes ) ? implode( ' ', (array) $menu_item->classes ) : null;
+		$id               = ( null !== $menu_item->object_id && 'custom' !== $menu_item->object ) ? $menu_item->object_id : null;
+		$opens_in_new_tab = null !== $menu_item->target && '_blank' === $menu_item->target;
+		$rel              = ( null !== $menu_item->xfn && '' !== $menu_item->xfn ) ? $menu_item->xfn : null;
+		$kind             = null !== $menu_item->type ? str_replace( '_', '-', $menu_item->type ) : 'custom';
+
+		$block = array(
+			'blockName' => isset( $menu_items_by_parent_id[ $menu_item->ID ] ) ? 'core/navigation-submenu' : 'core/navigation-link',
+			'attrs'     => array(
+				'className'     => $class_name,
+				'description'   => $menu_item->description,
+				'id'            => $id,
+				'kind'          => $kind,
+				'label'         => $menu_item->title,
+				'opensInNewTab' => $opens_in_new_tab,
+				'rel'           => $rel,
+				'title'         => $menu_item->attr_title,
+				'type'          => $menu_item->object,
+				'url'           => $menu_item->url,
+			),
+		);
+
+		$block['innerBlocks']  = isset( $menu_items_by_parent_id[ $menu_item->ID ] )
+			? gutenberg_global_parse_blocks_from_menu_items( $menu_items_by_parent_id[ $menu_item->ID ], $menu_items_by_parent_id )
+			: array();
+		$block['innerContent'] = array_map( 'serialize_block', $block['innerBlocks'] );
+
+		$blocks[] = $block;
+	}
+
+	return $blocks;
+}