add random match-making logic

.gitignore

@@ -33,5 +33,5 @@
 # Ignore key files for decrypting credentials and more.
 /main-server/config/*.key
 
-/frontend/node-modules
+/frontend/node_modules
 /frontend/dist

main-server/Gemfile

@@ -38,3 +38,5 @@ group :development, :test do
   gem "brakeman", require: false
   gem "rubocop-rails-omakase", require: false
 end
+
+gem "redis", "~> 6.0"

main-server/Gemfile.lock

@@ -250,6 +250,10 @@ GEM
       prism (>= 1.6.0)
       rbs (>= 4.0.0)
       tsort
+    redis (6.0.0)
+      redis-client (= 0.30.1)
+    redis-client (0.30.1)
+      connection_pool
     regexp_parser (2.12.0)
     reline (0.7.0)
       io-console (~> 0.5)
@@ -357,6 +361,7 @@ DEPENDENCIES
   puma (>= 5.0)
   rack-cors
   rails (~> 8.1.2)
+  redis (~> 6.0)
   rubocop-rails-omakase
   solid_cable
   solid_cache
@@ -459,6 +464,8 @@ CHECKSUMS
   rake (13.4.2) sha256=cb825b2bd5f1f8e91ca37bddb4b9aaf345551b4731da62949be002fa89283701
   rbs (4.2.0) sha256=51f7b886dcc05bc09e10b901daa6a81829f6adc03101d6ca9ea4aac6103e0674
   rdoc (8.0.0) sha256=03bf8c08a9639658855a0cfd77c0abca8325c227693f7f33f82957811348c469
+  redis (6.0.0) sha256=de71c10edd106986b759ec7ecdd08b63b9c0ee7414a0d0c1da73d31ba2bccda6
+  redis-client (0.30.1) sha256=5151bc5c7bbfe48623732cdae3b900d8a22dc691cc7cdfacfb351ac55116522d
   regexp_parser (2.12.0) sha256=35a916a1d63190ab5c9009457136ae5f3c0c7512d60291d0d1378ba18ce08ebb
   reline (0.7.0) sha256=5b012d8e55dbf9d450f12bde2cf7d15ff546ae80b3f8f3b30e570d431815583d
   rubocop (1.91.0) sha256=9c82b7bf391c5d7e3798c5b9996e22a1fe3bd7468e351dfdeb96140c058296d0

main-server/app/controllers/api/matchmaking_controller.rb

@@ -0,0 +1,21 @@
+class Api::MatchmakingController < ApplicationController
+  def create
+    result = MatchmakingService.find_match(current_user.id)
+
+    if result
+      render json: {
+        match_id: result[:match_id],
+        game_token: result[:game_token],
+        game_server: result[:game_server],
+        players: result[:players]
+      }
+    else
+      render json: { error: "No opponent found. Try again." }, status: :request_timeout
+    end
+  end
+
+  def destroy
+    MatchmakingService.cancel(current_user.id)
+    render json: { message: "Matchmaking cancelled" }
+  end
+end

main-server/app/services/matchmaking_service.rb

@@ -0,0 +1,122 @@
+class MatchmakingService
+  QUEUE_KEY = "matchmaking:queue"
+  LOCK_KEY = "matchmaking:lock"
+  MATCH_PREFIX = "matchmaking:match:"
+  MATCH_TTL = 60 # seconds
+  POLL_INTERVAL = 0.5 # seconds
+  MAX_WAIT = 30 # seconds
+
+  # Game server to redirect players to (hardcoded for now)
+  GAME_SERVER = ENV.fetch("GAME_SERVER_URL", "ws://game-server.example.com:8080")
+
+  class << self
+    # Main entry point: waits for an opponent and returns match data
+    def find_match(user_id)
+      user_id = user_id.to_i
+
+      # Try to pair with an existing waiting player
+      opponent_id = pop_opponent(user_id)
+
+      if opponent_id
+        create_match(user_id, opponent_id)
+      else
+        # Add self to queue and wait
+        add_to_queue(user_id)
+        wait_for_match(user_id)
+      end
+    end
+
+    # Cancel matchmaking (remove from queue)
+    def cancel(user_id)
+      RedisConnection.with do |redis|
+        redis.lrem(QUEUE_KEY, 0, user_id)
+      end
+    end
+
+    private
+
+    # Atomically pop an opponent from the queue (excluding self)
+    def pop_opponent(user_id)
+      RedisConnection.with do |redis|
+        redis.watch(QUEUE_KEY) do
+          queue = redis.lrange(QUEUE_KEY, 0, -1)
+          opponent = queue.find { |id| id.to_i != user_id }
+
+          if opponent
+            result = redis.multi do |tx|
+              tx.lrem(QUEUE_KEY, 0, opponent)
+            end
+            return opponent.to_i if result&.first&.positive?
+          else
+            redis.unwatch
+          end
+        end
+      end
+      nil
+    end
+
+    def add_to_queue(user_id)
+      RedisConnection.with do |redis|
+        # Remove any stale entries first
+        redis.lrem(QUEUE_KEY, 0, user_id)
+        redis.rpush(QUEUE_KEY, user_id)
+      end
+    end
+
+    def wait_for_match(user_id)
+      start_time = Time.current
+      match_id = nil
+
+      while Time.current - start_time < MAX_WAIT
+        RedisConnection.with do |redis|
+          match_id = redis.get("#{MATCH_PREFIX}#{user_id}")
+        end
+        break if match_id
+
+        sleep POLL_INTERVAL
+      end
+
+      if match_id
+        # Retrieve and delete the match data
+        data = nil
+        RedisConnection.with do |redis|
+          data = redis.get("#{MATCH_PREFIX}match:#{match_id}")
+          redis.del("#{MATCH_PREFIX}#{user_id}")
+          redis.del("#{MATCH_PREFIX}match:#{match_id}")
+        end
+        JSON.parse(data, symbolize_names: true) if data
+      else
+        # Timeout: remove from queue
+        cancel(user_id)
+        nil
+      end
+    end
+
+    def create_match(player1_id, player2_id)
+      match_id = SecureRandom.uuid
+      game_token = JwtService.encode(
+        match_id: match_id,
+        player1_id: player1_id,
+        player2_id: player2_id,
+        game_server: GAME_SERVER,
+        exp: 1.hour.from_now.to_i
+      )
+
+      match_data = {
+        match_id: match_id,
+        game_token: game_token,
+        game_server: GAME_SERVER,
+        players: [player1_id, player2_id]
+      }
+
+      # Store match data for both players
+      RedisConnection.with do |redis|
+        redis.set("#{MATCH_PREFIX}match:#{match_id}", match_data.to_json, ex: MATCH_TTL)
+        redis.set("#{MATCH_PREFIX}#{player1_id}", match_id, ex: MATCH_TTL)
+        redis.set("#{MATCH_PREFIX}#{player2_id}", match_id, ex: MATCH_TTL)
+      end
+
+      match_data
+    end
+  end
+end

main-server/config/initializers/redis.rb

@@ -0,0 +1,7 @@
+# Redis configuration
+# Development/test: localhost:6379 (default)
+# Production: set REDIS_URL env variable, e.g. redis://redis.example.com:6379/0
+
+RedisConnection = ConnectionPool.new(size: 5, timeout: 5) do
+  Redis.new(url: ENV.fetch("REDIS_URL", "redis://localhost:6380/0"))
+end

main-server/config/routes.rb

@@ -4,6 +4,9 @@ Rails.application.routes.draw do
     post   "login",    to: "sessions#create"
     delete "logout",   to: "sessions#destroy"
     get    "me",       to: "sessions#me"
+
+    post   "matchmaking", to: "matchmaking#create"
+    delete "matchmaking", to: "matchmaking#destroy"
   end
 
   # Reveal health status on /up that returns 200 if the app boots with no exceptions, otherwise 500.