class-map-co-authors.php

<?php
/**
 * Co-authors storage and retrieval.
 *
 * @package MultiAuthorPosts
 */

namespace MultiAuthorPosts;

/**
 * Manages the list of co-authors stored against each post.
 */
class Co_Authors {

	const META_KEY = '_map_co_authors';

	/**
	 * Register post meta on init.
	 */
	public static function init(): void {
		add_action( 'init', array( __CLASS__, 'register_meta' ) );
		add_action( 'post_updated', array( __CLASS__, 'preserve_previous_author' ), 10, 3 );
	}

	/**
	 * Register the co-authors post meta.
	 */
	public static function register_meta(): void {
		register_post_meta(
			'',
			self::META_KEY,
			array(
				'type'          => 'array',
				'description'   => 'Co-author user IDs for this post.',
				'single'        => true,
				'default'       => array(),
				'show_in_rest'  => false,
				'auth_callback' => function ( $allowed, $meta_key, $post_id ) {
					return current_user_can( 'edit_post', $post_id );
				},
			)
		);
	}

	/**
	 * Return the list of co-author user IDs for a post.
	 *
	 * @param int $post_id Post ID.
	 * @return int[]
	 */
	public static function get_co_authors( int $post_id ): array {
		$value = get_post_meta( $post_id, self::META_KEY, true );
		if ( ! is_array( $value ) ) {
			return array();
		}
		return array_map( 'intval', $value );
	}

	/**
	 * Add a user as a co-author of a post.
	 *
	 * No-ops silently if the user is already the post author or already a co-author.
	 *
	 * @param int $post_id Post ID.
	 * @param int $user_id User ID.
	 * @return bool Whether the operation succeeded.
	 */
	public static function add_co_author( int $post_id, int $user_id ): bool {
		$post = get_post( $post_id );
		if ( ! $post ) {
			return false;
		}

		if ( ! get_userdata( $user_id ) ) {
			return false;
		}

		// The post's original author never needs to be stored as a co-author.
		if ( (int) $post->post_author === $user_id ) {
			return true;
		}

		$co_authors = self::get_co_authors( $post_id );

		if ( in_array( $user_id, $co_authors, true ) ) {
			return true;
		}

		$co_authors[] = $user_id;
		return (bool) update_post_meta( $post_id, self::META_KEY, $co_authors );
	}

	/**
	 * Remove a user from the co-author list of a post.
	 *
	 * @param int $post_id Post ID.
	 * @param int $user_id User ID.
	 * @return bool Whether the operation succeeded.
	 */
	public static function remove_co_author( int $post_id, int $user_id ): bool {
		$co_authors = self::get_co_authors( $post_id );
		$filtered   = array_values( array_filter( $co_authors, fn( $id ) => $id !== $user_id ) );
		return (bool) update_post_meta( $post_id, self::META_KEY, $filtered );
	}

	/**
	 * Check whether a user is a co-author of a post.
	 *
	 * @param int $post_id Post ID.
	 * @param int $user_id User ID.
	 * @return bool
	 */
	public static function is_co_author( int $post_id, int $user_id ): bool {
		return in_array( $user_id, self::get_co_authors( $post_id ), true );
	}

	/**
	 * Return enriched co-author data (id, name, avatar) for a post.
	 *
	 * @param int $post_id Post ID.
	 * @return array<int, array{id:int,name:string,avatar:string}>
	 */
	public static function get_co_author_data( int $post_id ): array {
		$result = array();
		foreach ( self::get_co_authors( $post_id ) as $user_id ) {
			$user = get_userdata( $user_id );
			if ( ! $user ) {
				continue;
			}
			$result[] = array(
				'id'     => $user->ID,
				'name'   => $user->display_name,
				'avatar' => get_avatar_url( $user->ID, array( 'size' => 48 ) ),
			);
		}
		return $result;
	}

	/**
	 * When post authorship changes, preserve the previous author as a co-author.
	 *
	 * @param int      $post_id     Post ID.
	 * @param \WP_Post $post_after  Post object after the update.
	 * @param \WP_Post $post_before Post object before the update.
	 */
	public static function preserve_previous_author( int $post_id, \WP_Post $post_after, \WP_Post $post_before ): void {
		if ( (int) $post_before->post_author !== (int) $post_after->post_author ) {
			self::add_co_author( $post_id, (int) $post_before->post_author );
		}
	}
}