1 files changed, 54 insertions, 0 deletions
diff --git a/lib/gitlab/event_store/store.rb b/lib/gitlab/event_store/store.rb
new file mode 100644
index 00000000000..ecf3cd7e562
--- /dev/null
+++ b/lib/gitlab/event_store/store.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module EventStore
+    class Store
+      attr_reader :subscriptions
+
+      def initialize
+        @subscriptions = Hash.new { |h, k| h[k] = [] }
+
+        yield(self) if block_given?
+
+        # freeze the subscriptions as safety measure to avoid further
+        # subcriptions after initialization.
+        lock!
+      end
+
+      def subscribe(worker, to:, if: nil)
+        condition = binding.local_variable_get('if')
+
+        Array(to).each do |event|
+          validate_subscription!(worker, event)
+          subscriptions[event] << Gitlab::EventStore::Subscription.new(worker, condition)
+        end
+      end
+
+      def publish(event)
+        unless event.is_a?(Event)
+          raise InvalidEvent, "Event being published is not an instance of Gitlab::EventStore::Event: got #{event.inspect}"
+        end
+
+        subscriptions[event.class].each do |subscription|
+          subscription.consume_event(event)
+        end
+      end
+
+      private
+
+      def lock!
+        @subscriptions.freeze
+      end
+
+      def validate_subscription!(subscriber, event_class)
+        unless event_class < Event
+          raise InvalidEvent, "Event being subscribed to is not a subclass of Gitlab::EventStore::Event: got #{event_class}"
+        end
+
+        unless subscriber.respond_to?(:perform_async)
+          raise InvalidSubscriber, "Subscriber is not an ApplicationWorker: got #{subscriber}"
+        end
+      end
+    end
+  end
+end