Add instrumentation to command bus

lib/arkency/command_bus.rb

@@ -6,23 +6,45 @@ class CommandBus
     UnregisteredHandler = Class.new(StandardError)
     MultipleHandlers    = Class.new(StandardError)
 
-    def initialize
-      @handlers =
-        Concurrent::Map.new
+    def initialize(instrumentation = nil)
+      @handlers = Concurrent::Map.new
+      @instrumentation = instrumentation || NoOpInstrumentation.new
     end
 
     def register(klass, handler)
-      raise MultipleHandlers.new("Multiple handlers not allowed for #{klass}") if handlers[klass]
-      handlers[klass] = handler
+      raise MultipleHandlers, "Multiple handlers not allowed for #{klass}" if handlers[klass]
+
+      instrumentation.instrument(
+        'register.command_bus',
+        handler: handler,
+        klass: klass
+      ) do
+        handlers[klass] = handler
+      end
     end
 
     def call(command)
-      handlers
-        .fetch(command.class) { raise UnregisteredHandler.new("Missing handler for #{command.class}")  }
-        .(command)
+      handler = handlers.fetch(command.class) do
+        raise UnregisteredHandler, "Missing handler for #{command.class}"
+      end
+
+      instrumentation.instrument(
+        'call.command_bus',
+        handler: handler,
+        command: command
+      ) do
+        handler.call(command)
+      end
     end
 
     private
-    attr_reader :handlers
+
+    attr_reader :handlers, :instrumentation
+
+    class NoOpInstrumentation
+      def instrument(_name, payload = {})
+        yield payload if block_given?
+      end
+    end
   end
 end