<?php
/**
 * Move handler file.
 *
 * @package Activitypub
 */

namespace Activitypub\Handler;

use Activitypub\Collection\Followers;
use Activitypub\Collection\Remote_Actors;
use Activitypub\Http;

use function Activitypub\object_to_uri;

/**
 * Handle Move requests.
 *
 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-move
 * @see https://docs.joinmastodon.org/user/moving/
 * @see https://docs.joinmastodon.org/spec/activitypub/#Move
 */
class Move {
	/**
	 * Initialize the class, registering WordPress hooks.
	 */
	public static function init() {
		\add_action( 'activitypub_inbox_move', array( self::class, 'handle_move' ), 10, 2 );
	}

	/**
	 * Handle Move requests.
	 *
	 * @param array     $activity The JSON "Move" Activity.
	 * @param int|int[] $user_ids The user ID(s).
	 */
	public static function handle_move( $activity, $user_ids ) {
		$target_uri = self::extract_target( $activity );
		$origin_uri = self::extract_origin( $activity );

		if ( ! $target_uri || ! $origin_uri ) {
			return;
		}

		$target_json = Http::get_remote_object( $target_uri );
		$origin_json = Http::get_remote_object( $origin_uri );

		$verified = self::verify_move( $target_json, $origin_json );

		if ( ! $verified ) {
			return;
		}

		$target_object = Remote_Actors::get_by_uri( $target_uri );
		$origin_object = Remote_Actors::get_by_uri( $origin_uri );
		$result        = null;
		$success       = false;

		// If the origin is followed but the target is not, update the origin to point to the target.
		if ( \is_wp_error( $target_object ) && ! \is_wp_error( $origin_object ) ) {
			global $wpdb;
			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery
			$wpdb->update(
				$wpdb->posts,
				array( 'guid' => sanitize_url( $target_uri ) ),
				array( 'ID' => sanitize_key( $origin_object->ID ) )
			);

			// Clear the cache.
			\wp_cache_delete( $origin_object->ID, 'posts' );

			$success = true;
			$result  = Remote_Actors::upsert( $target_json );
		}

		// If both the target and origin are followed, merge them.
		if ( ! \is_wp_error( $target_object ) && ! \is_wp_error( $origin_object ) ) {
			$origin_users = \get_post_meta( $origin_object->ID, Followers::FOLLOWER_META_KEY, false );
			$target_users = \get_post_meta( $target_object->ID, Followers::FOLLOWER_META_KEY, false );

			// Get all user ids from $origin_users that are not in $target_users.
			$users = \array_diff( $origin_users, $target_users );

			foreach ( $users as $follower_user_id ) {
				\add_post_meta( $target_object->ID, Followers::FOLLOWER_META_KEY, $follower_user_id );
			}

			$success = true;
			$result  = \wp_delete_post( $origin_object->ID );
		}

		/**
		 * Fires after an ActivityPub Move activity has been handled.
		 *
		 * @param array $activity The ActivityPub activity data.
		 * @param int[] $user_ids The local user IDs.
		 * @param bool  $success  True on success, false otherwise.
		 * @param mixed $result   The result of the operation (e.g., post ID, WP_Error, or status).
		 */
		\do_action( 'activitypub_handled_move', $activity, (array) $user_ids, $success, $result );
	}

	/**
	 * Extract the target from the activity.
	 *
	 * The ActivityStreams spec define the `target` attribute as the
	 * destination of the activity, but Mastodon uses the `object`
	 * attribute to move profiles.
	 *
	 * @param array $activity The JSON "Move" Activity.
	 *
	 * @return string|null The target URI or null if not found.
	 */
	private static function extract_target( $activity ) {
		if ( ! empty( $activity['target'] ) ) {
			return object_to_uri( $activity['target'] );
		}

		if ( ! empty( $activity['object'] ) ) {
			return object_to_uri( $activity['object'] );
		}

		return null;
	}

	/**
	 * Extract the origin from the activity.
	 *
	 * The ActivityStreams spec define the `origin` attribute as source
	 * of the activity, but Mastodon uses the `actor` attribute as source
	 * to move profiles.
	 *
	 * @param array $activity The JSON "Move" Activity.
	 *
	 * @return string|null The origin URI or null if not found.
	 */
	private static function extract_origin( $activity ) {
		if ( ! empty( $activity['origin'] ) ) {
			return object_to_uri( $activity['origin'] );
		}

		if ( ! empty( $activity['actor'] ) ) {
			return object_to_uri( $activity['actor'] );
		}

		return null;
	}

	/**
	 * Verify the move.
	 *
	 * @param array $target_object The target object.
	 * @param array $origin_object The origin object.
	 *
	 * @return bool True if the move is verified, false otherwise.
	 */
	private static function verify_move( $target_object, $origin_object ) {
		// Check if both objects are valid.
		if ( \is_wp_error( $target_object ) || \is_wp_error( $origin_object ) ) {
			return false;
		}

		// Check if both objects are persons.
		if ( 'Person' !== $target_object['type'] || 'Person' !== $origin_object['type'] ) {
			return false;
		}

		// Check if the target and origin are not the same.
		if ( $target_object['id'] === $origin_object['id'] ) {
			return false;
		}

		// Normalize alsoKnownAs to an array (some JSON-LD payloads may use a string).
		$also_known_as = (array) ( $target_object['alsoKnownAs'] ?? array() );
		if ( empty( $also_known_as ) ) {
			return false;
		}

		// Collect all possible origin identifiers (id, url, webfinger).
		$origin_ids = array_filter(
			array(
				$origin_object['id'] ?? null,
				$origin_object['url'] ?? null,
				$origin_object['webfinger'] ?? null,
			)
		);

		// Check if any origin identifier is in the alsoKnownAs property of the target.
		if ( ! array_intersect( $origin_ids, $also_known_as ) ) {
			return false;
		}

		// Check if the origin has a movedTo property.
		if ( empty( $origin_object['movedTo'] ) ) {
			return false;
		}

		// Check if the movedTo property of the origin is the target.
		if ( $origin_object['movedTo'] !== $target_object['id'] ) {
			return false;
		}

		return true;
	}
}