1 files changed, 40 insertions, 0 deletions
diff --git a/lib/gitlab/github_import/milestone_finder.rb b/lib/gitlab/github_import/milestone_finder.rb
new file mode 100644
index 00000000000..208d15dc144
--- /dev/null
+++ b/lib/gitlab/github_import/milestone_finder.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module GithubImport
+    class MilestoneFinder
+      attr_reader :project
+
+      # The base cache key to use for storing/retrieving milestone IDs.
+      CACHE_KEY = 'github-import/milestone-finder/%{project}/%{iid}'.freeze
+
+      # project - An instance of `Project`
+      def initialize(project)
+        @project = project
+      end
+
+      # issuable - An instance of `Gitlab::GithubImport::Representation::Issue`
+      #            or `Gitlab::GithubImport::Representation::PullRequest`.
+      def id_for(issuable)
+        return unless issuable.milestone_number
+
+        Caching.read_integer(cache_key_for(issuable.milestone_number))
+      end
+
+      def build_cache
+        mapping = @project
+          .milestones
+          .pluck(:id, :iid)
+          .each_with_object({}) do |(id, iid), hash|
+            hash[cache_key_for(iid)] = id
+          end
+
+        Caching.write_multiple(mapping)
+      end
+
+      def cache_key_for(iid)
+        CACHE_KEY % { project: project.id, iid: iid }
+      end
+    end
+  end
+end