<?php
/**
 * WP_Classic_To_Block_Menu_Converter class
 *
 * @package WordPress
 * @since 6.3.0
 */

/**
 * Converts a Classic Menu to Block Menu blocks.
 *
 * @since 6.3.0
 */
class WP_Classic_To_Block_Menu_Converter {

    /**
     * Converts a Classic Menu to blocks.
     *
     * @since 6.3.0
     *
     * @param WP_Term $menu The Menu term object of the menu to convert.
     * @return string|WP_Error The serialized and normalized parsed blocks on success,
     *                         an empty string when there are no menus to convert,
     *                         or WP_Error on invalid menu.
     */
    public static function convert( $menu ) {

        if ( ! is_nav_menu( $menu ) ) {
            return new WP_Error(
                'invalid_menu',
                __( 'The menu provided is not a valid menu.' )
            );
        }

        $menu_items = wp_get_nav_menu_items( $menu->term_id, array( 'update_post_term_cache' => false ) );

        if ( empty( $menu_items ) ) {
            return '';
        }

        // Set up the $menu_item variables.
        // Adds the class property classes for the current context, if applicable.
        _wp_menu_item_classes_by_context( $menu_items );

        $menu_items_by_parent_id = static::group_by_parent_id( $menu_items );

        $first_menu_item = $menu_items_by_parent_id[0] ?? array();

        $inner_blocks = static::to_blocks(
            $first_menu_item,
            $menu_items_by_parent_id
        );

        return serialize_blocks( $inner_blocks );
    }

    /**
     * Returns an array of menu items grouped by the id of the parent menu item.
     *
     * @since 6.3.0
     *
     * @param array $menu_items An array of menu items.
     * @return array
     */
    private static function group_by_parent_id( $menu_items ) {
        $menu_items_by_parent_id = array();

        foreach ( $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
     *
     * @since 6.3.0
     *
     * @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.
     */
    private static function to_blocks( $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 ] )
            ? static::to_blocks( $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;
    }
}