Make it possible to define CI/CD config strategies

lib/gitlab/ci/config/entry/policy.rb

@@ -5,12 +5,29 @@ module Gitlab
         ##
         # Entry that represents a trigger policy for the job.
         #
-        class Policy < Node
-          include Validatable
+        class Policy < Simplifiable
+          strategy :RefsPolicy, if: -> (config) { config.is_a?(Array) }
+          strategy :ExpressionsPolicy, if: -> (config) { config.is_a?(Hash) }
+
+          class RefsPolicy < Entry::Node
+            include Entry::Validatable
 
             validations do
               validates :config, array_of_strings_or_regexps: true
             end
+
+            def value
+              { refs: @config }
+            end
+          end
+
+          class ExpressionsPolicy < Entry::Node
+            include Entry::Validatable
+
+            validations do
+              validates :config, type: Hash
+            end
+          end
         end
       end
     end

lib/gitlab/ci/config/entry/simplifiable.rb

+module Gitlab
+  module Ci
+    class Config
+      module Entry
+        class Simplifiable < SimpleDelegator
+          EntryStrategy = Struct.new(:name, :condition)
+
+          def initialize(config, **metadata)
+            strategy = self.class.strategies.find do |variant|
+              variant.condition.call(config)
+            end
+
+            entry = self.class.const_get(strategy.name)
+
+            super(entry.new(config, metadata))
+          end
+
+          def self.strategy(name, **opts)
+            EntryStrategy.new(name, opts.fetch(:if)).tap do |strategy|
+              (@strategies ||= []).append(strategy)
+            end
+          end
+
+          def self.strategies
+            @strategies || []
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/config/entry/policy_spec.rb

@@ -3,6 +3,7 @@ require 'spec_helper'
 describe Gitlab::Ci::Config::Entry::Policy do
   let(:entry) { described_class.new(config) }
 
+  context 'when using simplified policy' do
     describe 'validations' do
       context 'when entry config value is valid' do
         context 'when config is a branch or tag name' do
@@ -16,7 +17,7 @@ describe Gitlab::Ci::Config::Entry::Policy do
 
           describe '#value' do
             it 'returns key value' do
-            expect(entry.value).to eq config
+              expect(entry.value).to eq(refs: config)
             end
           end
         end
@@ -48,9 +49,13 @@ describe Gitlab::Ci::Config::Entry::Policy do
         describe '#errors' do
           it 'saves errors' do
             expect(entry.errors)
-            .to include 'policy config should be an array of strings or regexps'
+              .to include /policy config should be an array of strings or regexps/
           end
         end
       end
     end
+  end
+
+  context 'when using complex policy' do
+  end
 end