Prevent MQTT entities to be bound to AMQP exchanges

This is a temporary "hack" that can be removed when MQTT Exchanges and
Queues no longer inherit from AMQP entitites.

src/lavinmq/amqp/exchange/exchange.cr

@@ -137,6 +137,30 @@ module LavinMQ
         notify_observers(ExchangeEvent::Deleted)
       end
 
+      # This outer macro will add a finished macro hook to all inherited classes
+      # in LavinMQ::AMQP namespace.
+      macro inherited
+        {% if @type.name.starts_with?("LavinMQ::AMQP::") %}
+          # This macro will find the "bind" method of classes inhering from this class
+          # and redfine them to raise AccessRefused exception if the first argument
+          # isn't a type in LavinMQ::AMQP namespace.
+          #
+          # TODO remove this when LavinMQ::MQTT::Session no longer inherit from
+          # LavinMQ::AMQP::Queue and LavinMQ::MQTT::Exchange no longer inherit from
+          # lavinMQ::AMQP::Exchange
+        macro finished
+          \{% if (m = @type.methods.find(&.name.== "bind"))  %}
+            def bind(\{{ m.args.map(&.id).join(",").id}}) : Bool
+              unless \{{m.args[0].name.id}}.class.name.starts_with?("LavinMQ::AMQP::")
+                raise AccessRefused.new(self)
+              end
+              \{{ m.body }}
+          end
+         \{% end %}
+        end
+        {% end %}
+      end
+
       def bind(destination : LavinMQ::Destination, routing_key, headers = nil) : Bool
         raise AccessRefused.new(self)
       end