1 files changed, 73 insertions, 0 deletions
diff --git a/lib/gitlab/ci/variables/downstream/generator.rb b/lib/gitlab/ci/variables/downstream/generator.rb
new file mode 100644
index 00000000000..93c995cc918
--- /dev/null
+++ b/lib/gitlab/ci/variables/downstream/generator.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Variables
+      module Downstream
+        class Generator
+          include Gitlab::Utils::StrongMemoize
+
+          Context = Struct.new(:all_bridge_variables, keyword_init: true)
+
+          def initialize(bridge)
+            @bridge = bridge
+
+            context = Context.new(all_bridge_variables: bridge.variables)
+
+            @raw_variable_generator = RawVariableGenerator.new(context)
+            @expandable_variable_generator = ExpandableVariableGenerator.new(context)
+          end
+
+          def calculate
+            calculate_downstream_variables
+              .reverse # variables priority
+              .uniq { |var| var[:key] } # only one variable key to pass
+              .reverse
+          end
+
+          private
+
+          attr_reader :bridge, :all_bridge_variables
+
+          def calculate_downstream_variables
+            # The order of this list refers to the priority of the variables
+            # The variables added later takes priority.
+            downstream_yaml_variables +
+              downstream_pipeline_variables +
+              downstream_pipeline_schedule_variables
+          end
+
+          def downstream_yaml_variables
+            return [] unless bridge.forward_yaml_variables?
+
+            build_downstream_variables_from(bridge.yaml_variables)
+          end
+
+          def downstream_pipeline_variables
+            return [] unless bridge.forward_pipeline_variables?
+
+            pipeline_variables = bridge.pipeline_variables.to_a
+            build_downstream_variables_from(pipeline_variables)
+          end
+
+          def downstream_pipeline_schedule_variables
+            return [] unless bridge.forward_pipeline_variables?
+
+            pipeline_schedule_variables = bridge.pipeline_schedule_variables.to_a
+            build_downstream_variables_from(pipeline_schedule_variables)
+          end
+
+          def build_downstream_variables_from(variables)
+            Gitlab::Ci::Variables::Collection.fabricate(variables).flat_map do |item|
+              if item.raw?
+                @raw_variable_generator.for(item)
+              else
+                @expandable_variable_generator.for(item)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end