<?php
/**
 * Meta API: WP_Metadata_Lazyloader class
 *
 * @package WordPress
 * @subpackage Meta
 * @since 4.5.0
 */

/**
 * Core class used for lazy-loading object metadata.
 *
 * When loading many objects of a given type, such as posts in a WP_Query loop, it often makes
 * sense to prime various metadata caches at the beginning of the loop. This means fetching all
 * relevant metadata with a single database query, a technique that has the potential to improve
 * performance dramatically in some cases.
 *
 * In cases where the given metadata may not even be used in the loop, we can improve performance
 * even more by only priming the metadata cache for affected items the first time a piece of metadata
 * is requested - ie, by lazy-loading it. So, for example, comment meta may not be loaded into the
 * cache in the comments section of a post until the first time get_comment_meta() is called in the
 * context of the comment loop.
 *
 * WP uses the WP_Metadata_Lazyloader class to queue objects for metadata cache priming. The class
 * then detects the relevant get_*_meta() function call, and queries the metadata of all queued objects.
 *
 * Do not access this class directly. Use the wp_metadata_lazyloader() function.
 *
 * @since 4.5.0
 */
#[AllowDynamicProperties]
class WP_Metadata_Lazyloader {
    /**
     * Pending objects queue.
     *
     * @since 4.5.0
     * @var array
     */
    protected $pending_objects;

    /**
     * Settings for supported object types.
     *
     * @since 4.5.0
     * @var array
     */
    protected $settings = array();

    /**
     * Constructor.
     *
     * @since 4.5.0
     */
    public function __construct() {
        $this->settings = array(
            'term'    => array(
                'filter'   => 'get_term_metadata',
                'callback' => array( $this, 'lazyload_meta_callback' ),
            ),
            'comment' => array(
                'filter'   => 'get_comment_metadata',
                'callback' => array( $this, 'lazyload_meta_callback' ),
            ),
            'blog'    => array(
                'filter'   => 'get_blog_metadata',
                'callback' => array( $this, 'lazyload_meta_callback' ),
            ),
        );
    }

    /**
     * Adds objects to the metadata lazy-load queue.
     *
     * @since 4.5.0
     *
     * @param string $object_type Type of object whose meta is to be lazy-loaded. Accepts 'term' or 'comment'.
     * @param array  $object_ids  Array of object IDs.
     * @return void|WP_Error WP_Error on failure.
     */
    public function queue_objects( $object_type, $object_ids ) {
        if ( ! isset( $this->settings[ $object_type ] ) ) {
            return new WP_Error( 'invalid_object_type', __( 'Invalid object type.' ) );
        }

        $type_settings = $this->settings[ $object_type ];

        if ( ! isset( $this->pending_objects[ $object_type ] ) ) {
            $this->pending_objects[ $object_type ] = array();
        }

        foreach ( $object_ids as $object_id ) {
            // Keyed by ID for faster lookup.
            if ( ! isset( $this->pending_objects[ $object_type ][ $object_id ] ) ) {
                $this->pending_objects[ $object_type ][ $object_id ] = 1;
            }
        }

        add_filter( $type_settings['filter'], $type_settings['callback'], 10, 5 );

        /**
         * Fires after objects are added to the metadata lazy-load queue.
         *
         * @since 4.5.0
         *
         * @param array                  $object_ids  Array of object IDs.
         * @param string                 $object_type Type of object being queued.
         * @param WP_Metadata_Lazyloader $lazyloader  The lazy-loader object.
         */
        do_action( 'metadata_lazyloader_queued_objects', $object_ids, $object_type, $this );
    }

    /**
     * Resets lazy-load queue for a given object type.
     *
     * @since 4.5.0
     *
     * @param string $object_type Object type. Accepts 'comment' or 'term'.
     * @return void|WP_Error WP_Error on failure.
     */
    public function reset_queue( $object_type ) {
        if ( ! isset( $this->settings[ $object_type ] ) ) {
            return new WP_Error( 'invalid_object_type', __( 'Invalid object type.' ) );
        }

        $type_settings = $this->settings[ $object_type ];

        $this->pending_objects[ $object_type ] = array();
        remove_filter( $type_settings['filter'], $type_settings['callback'] );
    }

    /**
     * Lazy-loads term meta for queued terms.
     *
     * This method is public so that it can be used as a filter callback. As a rule, there
     * is no need to invoke it directly.
     *
     * @since 4.5.0
     * @deprecated 6.3.0 Use WP_Metadata_Lazyloader::lazyload_meta_callback() instead.
     *
     * @param mixed $check The `$check` param passed from the 'get_term_metadata' hook.
     * @return mixed In order not to short-circuit `get_metadata()`. Generally, this is `null`, but it could be
     *               another value if filtered by a plugin.
     */
    public function lazyload_term_meta( $check ) {
        _deprecated_function( __METHOD__, '6.3.0', 'WP_Metadata_Lazyloader::lazyload_meta_callback' );
        return $this->lazyload_meta_callback( $check, 0, '', false, 'term' );
    }

    /**
     * Lazy-loads comment meta for queued comments.
     *
     * This method is public so that it can be used as a filter callback. As a rule, there is no need to invoke it
     * directly, from either inside or outside the `WP_Query` object.
     *
     * @since 4.5.0
     * @deprecated 6.3.0 Use WP_Metadata_Lazyloader::lazyload_meta_callback() instead.
     *
     * @param mixed $check The `$check` param passed from the {@see 'get_comment_metadata'} hook.
     * @return mixed The original value of `$check`, so as not to short-circuit `get_comment_metadata()`.
     */
    public function lazyload_comment_meta( $check ) {
        _deprecated_function( __METHOD__, '6.3.0', 'WP_Metadata_Lazyloader::lazyload_meta_callback' );
        return $this->lazyload_meta_callback( $check, 0, '', false, 'comment' );
    }

    /**
     * Lazy-loads meta for queued objects.
     *
     * This method is public so that it can be used as a filter callback. As a rule, there
     * is no need to invoke it directly.
     *
     * @since 6.3.0
     *
     * @param mixed  $check     The `$check` param passed from the 'get_*_metadata' hook.
     * @param int    $object_id ID of the object metadata is for.
     * @param string $meta_key  Unused.
     * @param bool   $single    Unused.
     * @param string $meta_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
     *                          or any other object type with an associated meta table.
     * @return mixed In order not to short-circuit `get_metadata()`. Generally, this is `null`, but it could be
     *               another value if filtered by a plugin.
     */
    public function lazyload_meta_callback( $check, $object_id, $meta_key, $single, $meta_type ) {
        if ( empty( $this->pending_objects[ $meta_type ] ) ) {
            return $check;
        }

        $object_ids = array_keys( $this->pending_objects[ $meta_type ] );
        if ( $object_id && ! in_array( $object_id, $object_ids, true ) ) {
            $object_ids[] = $object_id;
        }

        update_meta_cache( $meta_type, $object_ids );

        // No need to run again for this set of objects.
        $this->reset_queue( $meta_type );

        return $check;
    }
}