1 files changed, 64 insertions, 0 deletions
diff --git a/app/services/groups/open_issues_count_service.rb b/app/services/groups/open_issues_count_service.rb
new file mode 100644
index 00000000000..db1ca09212a
--- /dev/null
+++ b/app/services/groups/open_issues_count_service.rb
@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+module Groups
+  # Service class for counting and caching the number of open issues of a group.
+  class OpenIssuesCountService < BaseCountService
+    include Gitlab::Utils::StrongMemoize
+
+    VERSION = 1
+    PUBLIC_COUNT_KEY = 'group_public_open_issues_count'
+    TOTAL_COUNT_KEY = 'group_total_open_issues_count'
+    CACHED_COUNT_THRESHOLD = 1000
+    EXPIRATION_TIME = 24.hours
+
+    attr_reader :group, :user
+
+    def initialize(group, user = nil)
+      @group = group
+      @user = user
+    end
+
+    # Reads count value from cache and return it if present.
+    # If empty or expired, #uncached_count will calculate the issues count for the group and
+    # compare it with the threshold. If it is greater, it will be written to the cache and returned.
+    # If below, it will be returned without being cached.
+    # This results in only caching large counts and calculating the rest with every call to maintain
+    # accuracy.
+    def count
+      cached_count = Rails.cache.read(cache_key)
+      return cached_count unless cached_count.blank?
+
+      refreshed_count = uncached_count
+      update_cache_for_key(cache_key) { refreshed_count } if refreshed_count > CACHED_COUNT_THRESHOLD
+      refreshed_count
+    end
+
+    def cache_key(key = nil)
+      ['groups', 'open_issues_count_service', VERSION, group.id, cache_key_name]
+    end
+
+    private
+
+    def cache_options
+      super.merge({ expires_in: EXPIRATION_TIME })
+    end
+
+    def cache_key_name
+      public_only? ? PUBLIC_COUNT_KEY : TOTAL_COUNT_KEY
+    end
+
+    def public_only?
+      !user_is_at_least_reporter?
+    end
+
+    def user_is_at_least_reporter?
+      strong_memoize(:user_is_at_least_reporter) do
+        group.member?(user, Gitlab::Access::REPORTER)
+      end
+    end
+
+    def relation_for_count
+      IssuesFinder.new(user, group_id: group.id, state: 'opened', non_archived: true, include_subgroups: true, public_only: public_only?).execute
+    end
+  end
+end