1 files changed, 83 insertions, 0 deletions
diff --git a/app/services/users/last_push_event_service.rb b/app/services/users/last_push_event_service.rb
new file mode 100644
index 00000000000..57e446d7f30
--- /dev/null
+++ b/app/services/users/last_push_event_service.rb
@@ -0,0 +1,83 @@
+module Users
+  # Service class for caching and retrieving the last push event of a user.
+  class LastPushEventService
+    EXPIRATION = 2.hours
+
+    def initialize(user)
+      @user = user
+    end
+
+    # Caches the given push event for the current user in the Rails cache.
+    #
+    # event - An instance of PushEvent to cache.
+    def cache_last_push_event(event)
+      keys = [
+        project_cache_key(event.project),
+        user_cache_key
+      ]
+
+      if forked_from = event.project.forked_from_project
+        keys << project_cache_key(forked_from)
+      end
+
+      keys.each { |key| set_key(key, event.id) }
+    end
+
+    # Returns the last PushEvent for the current user.
+    #
+    # This method will return nil if no event was found.
+    def last_event_for_user
+      find_cached_event(user_cache_key)
+    end
+
+    # Returns the last PushEvent for the current user and the given project.
+    #
+    # project - An instance of Project for which to retrieve the PushEvent.
+    #
+    # This method will return nil if no event was found.
+    def last_event_for_project(project)
+      find_cached_event(project_cache_key(project))
+    end
+
+    def find_cached_event(cache_key)
+      event_id = get_key(cache_key)
+
+      return unless event_id
+
+      unless (event = find_event_in_database(event_id))
+        # We don't want to keep querying the same data over and over when a
+        # merge request has been created, thus we remove the key if no event
+        # (meaning an MR was created) is returned.
+        Rails.cache.delete(cache_key)
+      end
+
+      event
+    end
+
+    private
+
+    def find_event_in_database(id)
+      PushEvent
+        .without_existing_merge_requests
+        .find_by(id: id)
+    end
+
+    def user_cache_key
+      "last-push-event/#{@user.id}"
+    end
+
+    def project_cache_key(project)
+      "last-push-event/#{@user.id}/#{project.id}"
+    end
+
+    def get_key(key)
+      Rails.cache.read(key, raw: true)
+    end
+
+    def set_key(key, value)
+      # We're using raw values here since this takes up less space and we don't
+      # store complex objects.
+      Rails.cache.write(key, value, raw: true, expires_in: EXPIRATION)
+    end
+  end
+end