1 files changed, 57 insertions, 0 deletions
diff --git a/lib/gitlab/github_import/representation/diff_notes/discussion_id.rb b/lib/gitlab/github_import/representation/diff_notes/discussion_id.rb
new file mode 100644
index 00000000000..38b560f21c0
--- /dev/null
+++ b/lib/gitlab/github_import/representation/diff_notes/discussion_id.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module GithubImport
+    module Representation
+      module DiffNotes
+        class DiscussionId
+          NOTEABLE_TYPE = 'MergeRequest'
+          DISCUSSION_CACHE_REGEX = %r{/(?<repo>[^/]*)/pull/(?<iid>\d+)}i.freeze
+          DISCUSSION_CACHE_KEY = 'github-importer/discussion-id-map/%{project}/%{noteable_id}/%{original_note_id}'
+
+          def initialize(note)
+            @note = note
+            @matches = note[:html_url].match(DISCUSSION_CACHE_REGEX)
+          end
+
+          def find_or_generate
+            (note[:in_reply_to_id].present? && current_discussion_id) || generate_discussion_id
+          end
+
+          private
+
+          attr_reader :note, :matches
+
+          def generate_discussion_id
+            discussion_id = Discussion.discussion_id(
+              Struct
+              .new(:noteable_id, :noteable_type)
+              .new(matches[:iid].to_i, NOTEABLE_TYPE)
+            )
+            cache_discussion_id(discussion_id)
+          end
+
+          def cache_discussion_id(discussion_id)
+            Gitlab::Cache::Import::Caching.write(
+              discussion_id_cache_key(note[:id]), discussion_id
+            )
+          end
+
+          def current_discussion_id
+            Gitlab::Cache::Import::Caching.read(
+              discussion_id_cache_key(note[:in_reply_to_id])
+            )
+          end
+
+          def discussion_id_cache_key(id)
+            format(DISCUSSION_CACHE_KEY,
+              project: matches[:repo],
+              noteable_id: matches[:iid].to_i,
+              original_note_id: id
+            )
+          end
+        end
+      end
+    end
+  end
+end