1 files changed, 44 insertions, 0 deletions
diff --git a/lib/gitlab/satellite/compare_action.rb b/lib/gitlab/satellite/compare_action.rb
new file mode 100644
index 00000000000..46c98a8f4ca
--- /dev/null
+++ b/lib/gitlab/satellite/compare_action.rb
@@ -0,0 +1,44 @@
+module Gitlab
+  module Satellite
+    class BranchesWithoutParent < StandardError; end
+
+    class CompareAction < Action
+      def initialize(user, target_project, target_branch, source_project, source_branch)
+        super user, target_project
+
+        @target_project, @target_branch = target_project, target_branch
+        @source_project, @source_branch = source_project, source_branch
+      end
+
+      # Compare 2 repositories and return Gitlab::CompareResult object
+      def result
+        in_locked_and_timed_satellite do |target_repo|
+          prepare_satellite!(target_repo)
+          update_satellite_source_and_target!(target_repo)
+
+          Gitlab::CompareResult.new(compare(target_repo))
+        end
+      rescue Grit::Git::CommandFailed => ex
+        raise BranchesWithoutParent
+      end
+
+      private
+
+      # Assumes a satellite exists that is a fresh clone of the projects repo, prepares satellite for diffs
+      def update_satellite_source_and_target!(target_repo)
+        target_repo.remote_add('source', @source_project.repository.path_to_repo)
+        target_repo.remote_fetch('source')
+      rescue Grit::Git::CommandFailed => ex
+        handle_exception(ex)
+      end
+
+      def compare(repo)
+        @compare ||= Gitlab::Git::Compare.new(
+          Gitlab::Git::Repository.new(repo.path),
+          "origin/#{@target_branch}",
+          "source/#{@source_branch}"
+        )
+      end
+    end
+  end
+end