[MM-52541] Mark files as deleted along with thread (#23226)

* mark thread files as deleted

* add missing check

* improve query

* Stopped rendering post preview if post is deleted

* Fixed lint error

* Fixed test

* updated types

* Removed deleted post from other post's embed data

* Added tests

* Apply suggestions from code review

Co-authored-by: Daniel Espino García <larkox@gmail.com>

* lint fix

---------

Co-authored-by: Konstantinos Pittas <konstantinos.pittas@mattermost.com>
Co-authored-by: Harshil Sharma <harshilsharma63@gmail.com>
Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Harshil Sharma <18575143+harshilsharma63@users.noreply.github.com>
Co-authored-by: Daniel Espino García <larkox@gmail.com>

server/channels/store/sqlstore/post_store.go

@@ -2913,6 +2913,30 @@ func (s *SqlPostStore) deleteThread(transaction *sqlxTxWrapper, postId string, d
 		return errors.Wrapf(err, "failed to mark thread for root post %s as deleted", postId)
 	}
 
+	return s.deleteThreadFiles(transaction, postId, deleteAtTime)
+}
+
+func (s *SqlPostStore) deleteThreadFiles(transaction *sqlxTxWrapper, postID string, deleteAtTime int64) error {
+	var query sq.UpdateBuilder
+	if s.DriverName() == model.DatabaseDriverPostgres {
+		query = s.getQueryBuilder().Update("FileInfo").
+			Set("DeleteAt", deleteAtTime).
+			From("Posts")
+	} else {
+		query = s.getQueryBuilder().Update("FileInfo", "Posts").
+			Set("FileInfo.DeleteAt", deleteAtTime)
+	}
+
+	query = query.Where(sq.And{
+		sq.Expr("FileInfo.PostId = Posts.Id"),
+		sq.Eq{"Posts.RootId": postID},
+	})
+
+	_, err := transaction.ExecBuilder(query)
+	if err != nil {
+		return errors.Wrapf(err, "failed to mark files of thread post %s as deleted", postID)
+	}
+
 	return nil
 }