Restores a post from the Trash.

function wp_untrash_post( $post_id = 0 ) {
	$post = get_post( $post_id );

	if ( ! $post ) {
		return $post;
	}

	$post_id = $post->ID;

	if ( 'trash' !== $post->post_status ) {
		return false;
	}

	$previous_status = get_post_meta( $post_id, '_wp_trash_meta_status', true );

	/**
	 * Filters whether a post untrashing should take place.
	 *
	 * @since 4.9.0
	 * @since 5.6.0 The `$previous_status` parameter was added.
	 *
	 * @param bool|null $untrash         Whether to go forward with untrashing.
	 * @param WP_Post   $post            Post object.
	 * @param string    $previous_status The status of the post at the point where it was trashed.
	 */
	$check = apply_filters( 'pre_untrash_post', null, $post, $previous_status );
	if ( null !== $check ) {
		return $check;
	}

	/**
	 * Fires before a post is restored from the Trash.
	 *
	 * @since 2.9.0
	 * @since 5.6.0 The `$previous_status` parameter was added.
	 *
	 * @param int    $post_id         Post ID.
	 * @param string $previous_status The status of the post at the point where it was trashed.
	 */
	do_action( 'untrash_post', $post_id, $previous_status );

	$new_status = ( 'attachment' === $post->post_type ) ? 'inherit' : 'draft';

	/**
	 * Filters the status that a post gets assigned when it is restored from the trash (untrashed).
	 *
	 * By default posts that are restored will be assigned a status of 'draft'. Return the value of `$previous_status`
	 * in order to assign the status that the post had before it was trashed. The `wp_untrash_post_set_previous_status()`
	 * function is available for this.
	 *
	 * Prior to WordPress 5.6.0, restored posts were always assigned their original status.
	 *
	 * @since 5.6.0
	 *
	 * @param string $new_status      The new status of the post being restored.
	 * @param int    $post_id         The ID of the post being restored.
	 * @param string $previous_status The status of the post at the point where it was trashed.
	 */
	$post_status = apply_filters( 'wp_untrash_post_status', $new_status, $post_id, $previous_status );

	delete_post_meta( $post_id, '_wp_trash_meta_status' );
	delete_post_meta( $post_id, '_wp_trash_meta_time' );

	$post_updated = wp_update_post(
		array(
			'ID'          => $post_id,
			'post_status' => $post_status,
		)
	);

	if ( ! $post_updated ) {
		return false;
	}

	wp_untrash_post_comments( $post_id );

	/**
	 * Fires after a post is restored from the Trash.
	 *
	 * @since 2.9.0
	 * @since 5.6.0 The `$previous_status` parameter was added.
	 *
	 * @param int    $post_id         Post ID.
	 * @param string $previous_status The status of the post at the point where it was trashed.
	 */
	do_action( 'untrashed_post', $post_id, $previous_status );

	return $post;
}