implement alternative match-making approach with Lua scripts in Redis

main-server/app/channels/application_cable/channel.rb

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+module ApplicationCable
+  class Channel < ActionCable::Channel::Base
+  end
+end

main-server/app/channels/application_cable/connection.rb

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+module ApplicationCable
+  class Connection < ActionCable::Connection::Base
+    identified_by :current_user
+
+    def connect
+      self.current_user = find_user
+      reject_unauthorized_connection unless current_user
+    end
+
+    private
+
+    def find_user
+      token = request.params[:token].presence ||
+              request.headers["Authorization"]&.split(" ")&.last
+      return unless token
+
+      decoded = JwtService.decode(token)
+      User.find_by(id: decoded[:user_id]) if decoded
+    end
+  end
+end

main-server/app/channels/matchmaking_channel.rb

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+# Real-time matchmaking channel.
+#
+# Client flow:
+#   1. Connect: ws(s)://host/cable?token=<JWT>
+#   2. Subscribe to "MatchmakingChannel"
+#   3. Send { action: "start", rating: <optional int> } to enter the queue
+#   4. Receive { type: "matched", ... } or { type: "timeout" }
+#   5. Disconnecting (or sending { action: "stop" }) cancels the search.
+class MatchmakingChannel < ApplicationCable::Channel
+  def subscribed
+    stream_for current_user
+
+    # If a match was found while this user had no subscription
+    # (e.g. brief reconnect), deliver it now — exactly once.
+    if match = MatchmakingService.claim(current_user.id)
+      transmit(match)
+    end
+  end
+
+  def start(data)
+    MatchmakingService.enqueue(current_user.id, rating: data["rating"])
+  end
+
+  def stop
+    MatchmakingService.cancel(current_user.id)
+  end
+
+  def unsubscribed
+    MatchmakingService.cancel(current_user.id)
+  end
+end