ChatManager = class ChatManager {
  /**
   * Constructor.
   *
   * @param {Collection} chats
   *   A Chats collection instance.
   */
  constructor(chats) {
    this.chats = chats;
  }

  /**
   * Order two comparable objects as min, max
   *
   * @param {Object} s1
   * @param {Object} s2
   * @returns {*[]}
   *   An array of the two objects, minimum first, maximum last.
   */
  static ordered(s1, s2) {
    let id1;
    let id2;
    // Ensure ordering as id1 <= id2. Equality should not happen, but handle it correctly nonetheless.
    if (s1 <= s2) {
      id1 = s1;
      id2 = s2;
    }
    else {
      id1 = s2;
      id2 = s1;
    }
    return [id1, id2];
  }

  /**
   * Find the id of a chat between two users.
   *
   * @param {String} myId
   *   The current user id.
   * @param {String} otherUserId
   *   The id of an other user.
   * @param {Session} session
   *   The session global.
   *
   * @returns {void}
   */
  assignChatId(myId, otherUserId, session) {
    let [user1Id, user2Id] = ChatManager.ordered(myId, otherUserId);

    // Since ids are ordered, we do not need a $or.
    const chat = this.chats.findOne({ user1Id, user2Id });
    // Meteor._debug(filter, chat);

    // No chat matching the filter - need to insert a new one.
    if (!chat) {
      Meteor.call("chats.insert", { user1Id, user2Id }, function (err, chatId) {
        if (err) {
          throw new Meteor.Error("access-denied", "Could not insert new chat.");
        }
        session.set("chatId", chatId);
        console.log("--- No chat found between " + user1Id + " and " + user2Id + ". Created " + chatId);
      });
    }
    // There is a chat going already - use that.
    else {
      const chatId = chat._id;
      session.set("chatId", chatId);
      console.log("--- Chat " + chatId + " found between " + user1Id + " and " + user2Id + ".");
    }
  }
};