Added EventBus, a simple global pub-sub event system.

lib/cyberarm_engine/event_bus.rb

@@ -0,0 +1,39 @@
+module CyberarmEngine
+  class EventBus
+    Subscriber = Data.define(:event, :listener, :method, :callback)
+    @subscribers = []
+
+    def self.subscribe(event, listener = nil, method = nil, &block)
+      raise "Subscriber cannot have both a method AND a callback block" if method && block_given?
+
+      subscriber = Subscriber.new(event, listener, method, block)
+      @subscribers << subscriber
+
+      subscriber
+    end
+
+    def self.unsubscribe(event, listener_or_subscriber)
+      @subscribers.delete_if { |s| s.event == event && (s == listener_or_subscriber || s.listener == listener_or_subscriber) }
+    end
+
+    def self.unsubscribe!(event)
+      @subscribers.delete_if { |s| s.event == event }
+    end
+
+    def self.announce(event, *payload)
+      subscribers = @subscribers.select { |s| s.event == event }
+
+      subscribers.each do |subscriber|
+        subscriber&.listener&.send(subscriber.method, *payload) if subscriber&.method
+        subscriber.callback&.call(*payload)
+      rescue StandardError => e
+        # TODO
+        warn "Failed to deliver event (#{event}) to listener (#{subscriber.inspect}): #{e}"
+      end
+    end
+
+    def self.publish(*args)
+      announce(*args)
+    end
+  end
+end