1 files changed, 61 insertions, 0 deletions
diff --git a/app/services/merge_requests/outdated_discussion_diff_lines_service.rb b/app/services/merge_requests/outdated_discussion_diff_lines_service.rb
new file mode 100644
index 00000000000..a2de5a32963
--- /dev/null
+++ b/app/services/merge_requests/outdated_discussion_diff_lines_service.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module MergeRequests
+  class OutdatedDiscussionDiffLinesService
+    include Gitlab::Utils::StrongMemoize
+
+    attr_reader :project, :note
+
+    OVERFLOW_LINES_COUNT = 2
+
+    def initialize(project:, note:)
+      @project = project
+      @note = note
+    end
+
+    def execute
+      end_position = position.line_range["end"]
+      diff_line_index = diff_lines.find_index do |l|
+        if end_position["new_line"]
+          l.new_line == end_position["new_line"]
+        elsif end_position["old_line"]
+          l.old_line == end_position["old_line"]
+        end
+      end
+      initial_line_index = [diff_line_index - OVERFLOW_LINES_COUNT, 0].max
+      last_line_index = [diff_line_index + OVERFLOW_LINES_COUNT, diff_lines.length].min
+
+      prev_lines = []
+
+      diff_lines[initial_line_index..last_line_index].each do |line|
+        if line.meta?
+          prev_lines.clear
+        else
+          prev_lines << line
+        end
+      end
+
+      prev_lines
+    end
+
+    private
+
+    def position
+      note.change_position
+    end
+
+    def repository
+      project.repository
+    end
+
+    def diff_file
+      position.diff_file(repository)
+    end
+
+    def diff_lines
+      strong_memoize(:diff_lines) do
+        diff_file.highlighted_diff_lines
+      end
+    end
+  end
+end