algorithm - Firebase: How to match opponents in a game?

Question

I'm implementing a social chess game. Every user can create a new game, and they'll wait until the system will find an opponent for them.

When user creates a game, they specify constraints: color they'd like to play, and opponent's minimal chess rating.

Opponents can either match or not match. For example, the following two opponents will match:

// User 1 with rating 1700              // User 2 with rating 1800
// creates this game                    // creates this game
game: {                                 game: { 
  color: 'white',                         minRating: 1650
  minRating: 1600                       }
}                                       // User did not specify a preferred color,
                                        // meaning they do not care which color to play

So, if User 1 is the first user in the system, and created their game, they'll wait. Once User 2 creates their game, they should be matched immediately with User 1.

On the other side, the following two opponents won't match, because they both want to play white. In this case, both should wait until someone else creates a game with color: 'black' (or color not specified), and minRating that would match the requirements.

// User 1 with rating 1700              // User 2 with rating 1800
// creates this game                    // creates this game
game: {                                 game: { 
  color: 'white',                         color: 'white'  
  minRating: 1600                         minRating: 1650
}                                       }

My concerns related to scenarios where thousands of users creates new games at the same time. How do I make sure that I match opponents without creating deadlocks? i.e. how do I prevent scenarios when User 1, User 2, and User 3 are trying to find an opponent at the same time, and their matching algorithms return User 99. How do I recover from this scenario, assigning User 99 to only one of them?

How would you use the power of Firebase to implement such a matching system?

Answer 1

Waitting for answers