<?php

namespace WPGraphQL\Utils;

class Preview {

	/**
	 * This filters the post meta for previews. Since WordPress core does not save meta for
	 * revisions this resolves calls to get_post_meta() using the meta of the revisions parent (the
	 * published version of the post).
	 *
	 * For plugins (such as ACF) that do store meta on revisions, the filter
	 * "graphql_resolve_revision_meta_from_parent" can be used to opt-out of this default behavior
	 * and instead return meta from the revision object instead of the parent.
	 *
	 * @param mixed       $default_value The default value of the meta
	 * @param int         $object_id     The ID of the object the meta is for
	 * @param string|null $meta_key      The meta key
	 * @param bool|null   $single        Whether the meta is a single value
	 *
	 * @return mixed
	 */
	public static function filter_post_meta_for_previews( $default_value, int $object_id, ?string $meta_key = null, ?bool $single = false ) {
		if ( ! is_graphql_request() ) {
			return $default_value;
		}

		/**
		 * Filters whether to resolve revision metadata from the parent node
		 * by default.
		 *
		 * @param bool    $should    Whether to resolve using the parent object. Default true.
		 * @param int     $object_id The ID of the object to resolve meta for
		 * @param ?string $meta_key  The key for the meta to resolve
		 * @param ?bool   $single    Whether a single value should be returned
		 */
		$resolve_revision_meta_from_parent = apply_filters( 'graphql_resolve_revision_meta_from_parent', true, $object_id, $meta_key, $single );

		if ( false === $resolve_revision_meta_from_parent ) {
			return $default_value;
		}

		$post = get_post( $object_id );

		if ( ! $post instanceof \WP_Post ) {
			return $default_value;
		}

		if ( 'revision' === $post->post_type ) {
			$parent   = get_post( $post->post_parent );
			$meta_key = ! empty( $meta_key ) ? $meta_key : '';

			$parent_meta = isset( $parent->ID ) && absint( $parent->ID ) ? get_post_meta( $parent->ID, $meta_key, (bool) $single ) : $default_value;

			// Wrap in array in case of single as get_post_metadata filter returns first value from array when single.
			// Ref: https://github.com/WordPress/wordpress-develop/blob/2fe26ceb7a1f3fb57ec8726fc5f425d00a12ace9/src/wp-includes/meta.php#L666
			return ( $single && is_array( $parent_meta ) ) ? [ $parent_meta ] : $parent_meta;
		}

		return $default_value;
	}
}