Add basic implementation of cross project pipeline service

ee/app/models/ee/ci/bridge.rb

@@ -6,6 +6,7 @@ module EE
       extend ActiveSupport::Concern
 
       prepended do
+        serialize :options # rubocop:disable Cop/ActiveRecordSerialize
         has_many :sourced_pipelines, class_name: ::Ci::Sources::Pipeline,
                                      foreign_key: :source_job_id
 
@@ -35,7 +36,19 @@ module EE
       end
 
       def schedule_downstream_pipeline!
-        raise NotImplementedError
+        CreateCrossProjectPipelineWorker.perform_async(self.id)
+      end
+
+      def target_user
+        self.user
+      end
+
+      def target_project_name
+        options.dig(:trigger, :project)
+      end
+
+      def target_ref
+        options.dig(:trigger, :branch)
       end
     end
   end

ee/app/services/ci/create_cross_project_pipeline_service.rb

+# frozen_string_literal: true
+
+module Ci
+  class CreateCrossProjectPipelineService < ::BaseService
+    include Gitlab::Utils::StrongMemoize
+
+    def execute(bridge)
+      @bridge = bridge
+
+      unless can_create_cross_pipeline?
+        return bridge.drop!(:insufficient_permissions)
+      end
+
+      create_pipeline do |pipeline|
+        source = bridge.sourced_pipelines.build(
+          source_pipeline: bridge.pipeline,
+          source_project: bridge.project,
+          project: target_project,
+          pipeline: pipeline)
+
+        pipeline.source_pipeline = source
+      end
+    end
+
+    private
+
+    def can_create_cross_pipeline?
+      can?(current_user, :create_pipeline, project) &&
+        can?(current_user, :create_pipeline, target_project) &&
+        can?(@bridge.target_user, :create_pipeline, target_project)
+    end
+
+    def create_pipeline
+      ::Ci::CreatePipelineService
+        .new(target_project, @bridge.target_user, ref: @bridge.target_ref)
+        .execute(:pipeline, ignore_skip_ci: true) do |pipeline|
+          yield pipeline
+        end
+    end
+
+    def target_project
+      strong_memoize(:target_project) do
+        Project.find_by_full_path(@bridge.target_project_name)
+      end
+    end
+  end
+end

ee/app/workers/ci/create_cross_project_pipeline_worker.rb

+# frozen_string_literal: true
+
+class CreateCrossProjectPipelineWorker
+  include ::ApplicationWorker
+  include ::PipelineQueue
+
+  def perform(bridge_id)
+    ::Ci::Bridge.find(bridge_id).try do |bridge|
+      ::Ci::CreateCrossProjectPipelineService
+        .new(bridge.project, bridge.user)
+        .execute(bridge)
+    end
+  end
+end